2 The automatic processing flowchart for aerial image

Figure 2. The automatic processing flowchart for aerial image

Currently in MASI Version 6.0 there is not a function of aero-triangulation for aerial images, but the results of aero-triangulation from mainstream software can be used in MASI software. Experimental results show that the results of aero-triangulation from Inpho, PhotoMOD, PATB, Bingo, BLUH, PixelGrid, and Geolord_AT can be used in MASI software.

In the flowchart, each step corresponds to a function in aerial modules as follows:

(1) Automatic stereo matching and DSM generation. According to the lists of exterior elements of images in an aerial block, the program fulfills stereo matching for all stereo pairs and generates dense point clouds for each stereo pair (users can decide whether the text-formatted point clouds files with extension .xyz are saved by setting the configuration option; in this file each line is for one point). Then, these point clouds are transformed to DSMs and these DSMs are mosaicked. At last, a mosaicked DSM covering the whole aerial block is generated (the DSM before interpolation). Clicking the icon showing “DSM” in the main interface,

The following menu will pop up.

The command item, Easily used Model, in the menu is to call the function of stereo matching and DSM generation. After processing, a mosaicked DSM (the DSM before interpolation) is generated. The program not only supports parallel computing of multi-threads and multi-processors provided by a single machine, but also has the ability to distribute all images of the whole block to multiple machines evenly. Users can also adopt the flexibly connected model to generate DSM. It has relatively more steps, but is flexible to connect these steps, and is able to manually distribute processing tasks to multiple machines. Using this flexibly connected model, users can interrupt and resume the task at any time. Usually users who use the flexibly connected model need to know the software and the principle behind the software more. Recommendations are given that at the beginning users can choose the easily used method while users who already have some experiences after a period of time can choose the flexibly connected method. The description of easily used model is only given in this this tutorial. For details about flexibly connected model, please refer to user manual.

(2) Post processing for DSM: The above mosaicked DSM has some areas which have not height value (before interpolation these areas are filled by using no-data values). In this step, these areas with no-data value are interpolated, and outliers (or small spots of errors) in the resultant DSM after interpolation are removed. The output of this step is the product of dense DSM, which is generated by this software. The DSM product can be used in different applications followed (e.g., volume calculation, finding change of surface height, extraction of the height of building / tree). The command item, Post Processing, in the menu is to call the function of post processing for DSM.

(3) Automatic true ortho-rectification: The program uses the DSM source generated in Step 2 to ortho-rectify all images in an aerial block. For each image, an ortho-rectified image is generated. These ortho-rectified images are mosaicked and an ortho-mosaic image covering the whole aerial block is generated. An alternative way is that DTM as a height source, which can be from third party or generated by MASI software, is used to ortho-rectify images. This way is more common. Because DSM generated by MASI software is highly dense and has high quality, we highly recommend that the highly dense DSM is used to fulfill true ortho-rectification if the overlapping between images is high (e.g., the flight / side overlapping ratio is 80/60). Clicking the icon showing “True Ortho” in the main interface,

The following menu will pop up.

The command item, Aerial Ortho, in the above menu is to call the function of ortho-rectification. After processing, an ortho-mosaicked image is generated.

(4) Comparing surface height and change finding. By comparing DSMs of different phases (generated by MASI software), the program can automatically find change of the surface height and calculate the value of changed height. It can be used in the automatic finding of new buildings, the unplanned buildings and the removed buildings, and estimating their corresponding accurate height. The map of height difference produced in this step can be used in the following extraction of building attributes (the center position of building, height of building, number of layers, area of ground, and construction area of building). Clicking the icon showing “Surface Change” in the main interface,

The operating interface of the function will be launched.

(5) Automatic DSM2DTM: The program deletes the non-grounded objects like buildings, trees in DSM and transforms DSM to DTM where the pure ground height is saved. Clicking the icon showing “DSM to DTM” in the main interface,

The operating interface of the function will be launched.

(6) Height estimation of building / tree. The height difference between DSM and DTM (nDSM) is the height of building / tree. The height difference (raster form) produced in this step can be used in the following extraction of building attributes (the center position of building, height of building, number of layers, area of ground, and construction area of building). DSM is generated by the functions in MASI software (including post processing for DSM), and DTM can be produced in the step 5 in this flowchart. Clicking the icon showing “Building height” in the main interface,

The operating interface of the function will be launched.

(7) Applications. The generated dense DSM, map of height difference, nDSM (i.e., height of building / tree) in above steps can be passed to the application functions which fulfill volume calculation and extraction of building attributes (the center position of building, height of building, number of layers, area of ground, and construction area of building). Clicking the icon showing “App” in the main interface,

The following menu will pop up.

Currently two applications modules are included, i.e., volume calculation and automatic extraction of building attributes in the light of buildings footprints. The command item, Calculate Volume, in the above menu is to call the function of volume calculation. The GUI program called from the command item is calVolumeForm.exe. Also, the GUI program can be launched by double-clicking the program directly. For more details, please refer to “Usage of the calVolume.exe and calVolumeForm.exe programs”. The command item, Extract Buildings’ Attributes, in the above menu is to call the function of extraction of building attributes. The GUI program called from the command item is extBldgAttributesForm.exe. Also, the GUI program can be launched by double-clicking the program directly. For more details, please refer to “Usage of the extBldgAttributes.exe and extBldgAttributesForm.exe programs”. In the course of volume calculation and automatic extraction of building attributes, the bounds in the form of polygon are needed. Users can click the command item, Polygons Drawing Tool, in above menu to launch the interactive tool, collectPolygons.exe, to collect polygons and save them.

(8) 3D modeling with true color textures. Images and highly dense DSM generated in previous steps are used to generate 3D TIN models with true color textures. The 3D models are in a form of tiled mesh. The data type of the images which are used for texture mapping is unsigned 8 bit integer. If it is not, user should stretch the images to unsigned 8 bit using the autoStretch.exe program provided by MASI software. Clicking the icon showing “Textured 3D Model” in the main interface,

The following menu will pop up.

The command item, textured 3D modeling, in the above menu is to call the function of 3D modeling. The GUI program called from the command item is aerialScene3DForm.exe. Also, the GUI program can be launched by double-clicking the program directly. For more details, please refer to “Usage of the aerialScene3D.exe and aerialScene3DForm.exe programs”.

In addition, other functions are included: image displaying, interactively editing of DSM/DEM, collecting polygons, automatic mosaic (mosaic of DSMs, mosaic of ortho-rectified images, mosaic of histogram matched images), transforming RGB image to grey image, rotation of image, reflection of image, transforming point clouds to surface in the form of raster, transforming DSM with raster form to point clouds, image cropping, creating overviews for image.

The method of format transform for point clouds generated by MASI software: the file of point clouds generated by the software is text format, which can be transformed to LAS format through the following steps. In the course of transform, a third party software package OSGeo4W (including the open source library, i.e., libLAS) is exploited. The package can be downloaded from the official website of OSGeo4W. The steps are as follows:

(1) Translation to LAS format: the command, namely txt2las.exe (OSGeo4W package includes the program), in the open source library, libLAS, can be used to translate the point clouds with text format to the LAS file. The corresponding command is as follows:

>txt2las.exe -parse xyz -i filename.xyz -o filename.las

(2) Assigning RGB values: the command, namely las2las.exe (OSGeo4W package includes the program), in the open source library, libLAS, can be used to assign the RGB values from truly ortho-rectified image to the points in LAS point clouds file. The colored point clouds are obtained. One example of the command is as follows:

>las2las.exe -i points.las --color-source ortho.tif -o points_rgb.las --file-format 1.2 --point-format 3 --color-source-scale 256 --color-source-bands 1 2 3

First, all files required in the course of automatic stereo matching and DSM generation, such as images, the file of interior parameters of camera, and the list file of exterior elements, are copied to a directory, e.g., I:\points\images, and set it as work directory. When MASI graphical interface is used, all required files should be put in the same directory and the directory is set as work directory.

The file of interior parameters of camera is interiorfile.dat. The format of file is as follows:

Defining of each line in the file (the definition of the underlying coordinate system is outlined in Appendix III of user manual):

Line 1 is the X coordinate of principal point in image coordinate system;

Line 2 is the Y coordinate of principal point in image coordinate system;

Line 3 is the X coordinate (Unit: mm) of principal point in camera coordinate system (the center of the camera as the original point in the coordinate system);

Line 4 is the Y coordinate (Unit: mm) of principal point in camera coordinate system (the center of the camera as the original point in the coordinate system);

Line 5 is the focal length of the camera (Unit: mm);

Line 6 is the pixel size of the camera (Unit: mm).

Users can create a new file of interior parameters of camera and save it by clicking the “new” button in the interface. The operating form to create a file of interior parameters is as follows:

Each item in the form exactly corresponds to the item in the file of interior parameters of camera. The advantage is to operate easily. Recommendation is given that at the beginning users utilize the interface of the “new” to create a file of interior parameters of camera.

The content of the list file of exterior elements is as follows:

…

Each line corresponds to exterior elements of an image, and these lines are arranged in sequence. First element is the image ID which is followed by six exterior elements (Attention: the first element, image ID, do not include extension of image file). The contents after the six elements are discarded. The six elements are three linear elements and three angle elements. The order of these exterior elements can be either first linear elements then angle elements, or first angle elements then linear elements. The format of oriList.dat can also be the output format of PATB software (i.e., the rotation system is indicated by rotation matrix directly). For more details, please refer to user manual.

In this case, exterior elements included in oriList.dat are formulated as follows: first linear elements then angle elements, omega-phi-kappa rotation system. The unit of rotational angle is degree. The exterior elements from different software, such as Inpho, PhotoMOD, PixelGrid, may have different formats in terms of order between linear and angle elements, rotation system, and the unit of angle, comparing with this case in the sample. Users should set the provided three options in the interface (Order of exterior elements, Rotation system, and Unit of angle), according to the real case of the exterior elements. The different combination of the values of three options provided in this software can support almost all formats of exterior elements from the available aero-triangulation software. For more details, please refer to the sections of stereo matching and DSM generation for aerial images in user manual.

Extension of image in the configuration options means the adopted format of images. It can be TIFF or JPEG, which are commonly used format for aerial image. The following three options should be set according to the real case of the exterior elements. In this sample, the selected values of the three options are shown in the above figure of the operating interface.

Height limit has three choices: determined by program, setting maximum and minimum heights from right side, and selecting third part elevation file (The coordinate system of elevation file must be the same as that of exterior elements), respectively. If users choose to set height limit from right side, the maximum and minimum heights are values of surface height (including height of the man-made objects) of the highest and lowest points above sea level in the aerial block. The height value above sea level is based on the adopted coordinates system. The maximum and minimum height value of elevation can be extended, to some extent, i.e., increasing the maximum value a little bit and decreasing the minimum value a little bit.

Rotation or not first: whether image should be rotated in advance. For some cases, a specific rotation is required: the layout of image that is used to determine orientation of image is different from the layout of image which is saved in computer and used as input of the program. There are four cases: none rotation, rotation of clockwise 90 degree; rotation of anti-clockwise 90 degree, and rotation of 180 degree. In this sample, no rotation is needed in advance. If the exterior elements with PATB format exported by Inpho software are adopted, the images before stereo matching may need to be rotated 180 degree because the directions of coordinates defined in Inpho software are different. Users can set to rotate images 180 degree via the option.

Format of intermediate files: the intermediate files are epipolar and disparity images whose file format can be configured. The formats, such as GTiff and ERDAS IMAGINE (.img), can be used.

Ratio of image size: the ratio of the size of original image to the size of matched image. The size of matched image can be the same as the original image, or can be reduced in the light of some specific scale. Two cases are supported in the software: 1 means the size of matched image in each dimension is the same as the original image, while 2 means the size of matched image is the 1/2 size of the original image in each dimension. Reduction of size in the course of stereo matching can lead to reduction of computational requirement and of the amount of data, and also accelerate the process. But it also leads to the loss of precision, decrease of the density of points. Users can select the value in the light of specific requirements.

Delete intermediate files or not: users can determine whether the intermediate files (epipolar and disparity images) are deleted by setting the option. The epipolar images can be used in the stereo displaying and further in the line-drawing in the stereo displaying.

Method to select height value: the method how to select the height value when there are multiple 3D points in a grid. The software supports three methods: max, min, average, which select maximum, minimum, average height value, respectively. The recommended method is max.

Save point clouds or not: users can determine whether point clouds generated from each stereo pair are saved as a text-formatted file with extension .xyz. The default setting is no-saving.

Tiles and overlapped size between tiles: tiles into which the whole image is divided and overlapped size is the extended pixels for each tile. 2 means the whole image is divided to 2 tiles along the image height direction, and in the course of matching each tile is extended 512 pixels in the two ends. This option is useful for the situation where the image frame is very large and the memory of used computer is limited. If the number of tiles is set as 1, the image is not divided.

Partitions and Part ID: The two parameters are used for distributed computing on multiple machines. The program, aerialDSM.exe, can equally partition all images of the whole block into different parts, in the light of the number of used computers. Each part corresponds to a computer and is identified by a serial number. The serial number is 0-based and integer type, its range is 0 ~ (Partitions - 1). For the default setting in this form, partitions are 1, which means only one computer is used for computation. All images are treated as one part and are processed on this machine whose part ID is 0. Attention: MASI software need to be installed on all computers used for computation and it should be ensured that all used files including images, the list file exterior elements of the whole block, the file of interior parameters of the camera and the configuration file are accessed by each machine.

Number of used threads per processor: setting the number of used threads (CPU cores or the virtual CPU cores by using hyper-threading technology) per processor. For the cases where CPU cores are enough, we suggest that number of 4, 6 or 8 is set here.

Bounding polygon: users can determine whether a bounding polygon is used to limit the region of stereo matching. After checking the checkbox, a shape format file which includes a polygon for bounding should be selected. Compared to the region bounded by the used polygon, the resultant region after the utilization of bounding polygon in stereo matching may be extended a little bit. The bounding polygon file can include only one polygon and its coordinate system must be the same as that of exterior elements. For default setting, bounding polygon is not used. The button of “Selecting File” in the right side is invalid.

After the above options in the interface are set, users can click “Save Configuration” to save these options. These configuration options will be saved in a configuration file, aerialDSM.conf, and next time the options can be loaded from the configuration file by clicking “Load Configuration”. The configuration file, aerialDSM.conf, is also stored in the work directory. If “Execute” is clicked, the configuration file will also be generated in the same way.

In the output setting, users should set the filename of the mosaicked DSM (the DSM before interpolation), the grid spacing (cell size) of the raster file used to store height value (the value of grid spacing can not be better than the actual ground sample distance, GSD, of image), the no-data value used to fill in the area without height value in the raster DSM file (no-data value).

Because the computational requirements for stereo matching are large, the software supports parallel computing to leverage advances of the multi-core computer. Serial or parallel processing can be selected. If parallel processing is selected, number of processors should be inputted as well as the current user name using the Windows OS and password of the user. Next time users can load the information by clicking the load button, and do not need input the information again. Users should be very careful when selecting the number of processors, which should be determined in the light of the number of available CPU cores in the adopted machine, the size of physical memory and the size of image frame. There are three points for selecting the number of processors. First, the product of the value set in the option, Number of used threads per processor, and the number of used processors here can not exceed the total number of CPU cores (or the virtual CPU cores by using hyper-threading technology). Second, all consumed memory can not exceed the physical memory on the machine. For the case where an image is divided into two tiles and then is processed, 8 G - 16 G memory is consumed in one processor, generally. If tile-dividing is not used, the consumed memory will be two times. Also, the consumed memory is related to the size of image. The bigger the size, the more is the memory consumed. The total number, i.e., multiplication of the number of processors by the memory consumed in a processor, can not exceed the physical memory on the machine. Third, requirements of disk reading and writing brought by multiprocessor processing can not exceed the disk capability provided by the machine. User can get the information of consumed memory from Task Manager of Windows OS, and the information of busy intensity of disk reading and writing and its speed from Resource Monitor of Windows OS. Users who want to use parallel computing in the software should be trained for a period of time, and know the software and the principle behind the software more. At the beginning, ordinary users are not expected to use parallel computing. In the course of using parallel computing, if there are any problems encountered, please contact us as soon as possible.

After finishing the setting of configuration options, input and output setting, users can click the button of “Execute”. The program starts to run and the required time to finish the whole procedure is different according to the size of the aerial block. In the course of computation, the buttons of “Execute” and “Cancel” on the bottom of the form is invalid. The two buttons can not be clicked in case they are clicked many times in the course of running. Users can learn the progress and the running status via the re-directed output printing (sometime printing may delay) on the right side. User can also check the information of resources (CPU, memory and Disks) possessed by the program from Task Manager and Resource Monitor of Windows OS. Once the execution of aerialDSM.exe is finished, a message box will pop up showing that the processing is closed successfully or terminated (aborted). After clicking OK button on the message box, the GUI program returns to the available status. Users can either click the button of “Cancel” on the bottom or click the closing icon on the up-right corner of the interface to close this GUI program. Or users can select and set new input and output to fulfill a new task.

User can click the button of “Terminate” on the bottom if they need to abort the processing (not the closing of GUI form). The GUI program, aerialDSMForm.exe, will kill the process of aerialDSM.exe which is being called. Killing the process of aerialDSM.exe may delay (less than one second or several seconds). Once the process is killed, a message box will pop up showing that the processing is terminated (aborted) or closed successfully. After clicking OK button on the message box, the GUI program returns to the available status. Users can either click the button of “Cancel” on the bottom or click the closing icon on the up-right corner of the interface to close this GUI program. Or users can select and set new input and output to fulfill a new task.

Attention: the button of “Cancel” on the bottom is only for closing the GUI program. If the called logical program (i.e., aerialDSM.exe) is running, users should first click the button of “Terminate” to abort the processing task or wait until the processing task is finished, and then close the GUI program. Users can not click the button of “Cancel” or click the closing icon on the up-right corner of the interface to close this GUI program when the called logical program is running.

The blank area of the right side will display the information printed by the command program, and the printed information will also be saved in a log file named as aerialDSM_ddMMMyyyyHHmmss_log.txt. In the filename, dd are two digital numbers indicating a date, MMM are three English characters indicating an abbreviation of a month, yyyy are four digital numbers indicating a year, and HHmmss are digital numbers indicating hour, minute and second in the form of 24 hours.

All configuration options are saved in the configuration file, aerialDSM.conf, through a certain type of form, in the course of running of program. The user name and password used in the parallel processing are saved in the file named as pwd.txt (If parallel processing is not used, there is no such file). The configuration file, aerialDSM.conf, can be used in the function, Load Configuration. The file, pwd.txt, can be used to load user name and the password which are used in the parallel processing. The printed information in the course of running is saved in a log file named as aerialDSM_ddMMMyyyyHHmmss_log.txt.

In the course of running of the program, the intermediate files, i.e., epipolar and disparity images are generated (these intermediate files can remain or be deleted according to the corresponding configuration option). A text-formatted file of point clouds with extension .xyz is generated for each stereo pair, if point clouds are set to be saved. In this file, each line corresponds to one point. A mosaicked DSM covering the whole aerial block (if the default case is adopted, partitions are 1, which means only one computer is used for computation) is generated (the filename is set in output DSM file in output setting in the interface, and DSM is the one before interpolation). If point clouds are set to be saved, a list file named “points_part%d_of_%dparts_List.txt” is generated at the same time. The first %d from left to right in the filename is replaced by the serial number of the partition (partID) and the second %d is replaced by the number of partitions (Partitions). The list file includes all filenames of point clouds extracted from stereo pairs which are distributed to the machine. The format of the list is as follows:

01_02_points.xyz

05_06_points.xyz

09_10_points.xyz

13_14_points.xyz

17_18_points.xyz

21_22_points.xyz

….

All these files are stored in the work directory. Except the above mentioned files, other files generated will be deleted in the end of the program.

A useful method to decide if arguments, parameters setting and command operations in this step are correct is to check if the objects in the generated epipolar pair are aligned strictly in horizontal direction. The vertical swipe function in the module of image viewer, imgViewer.exe, provided by MASI software can be used to view horizontal alignment. For more details, please refer to the program usage of imgViewer.exe.

The DSM result obtained in this step is the DSM before interpolation, which needs to pass to the next step (i.e., post processing for DSM) to yield the final highly dense DSM. Before post processing for DSM, if the un-interpolated DSM has big areas of mismatching (e.g., water body, cloud and snow covered area, area with repeated textures) which can be found by the manner of visual checking, the interactive tool for editing DSM/DEM (i.e., collectPolygons.exe) can be used to edit the DSM with big areas of mismatching. For more details, please refer to “Usage of the collectPolygons.exe program”.

Step 2: Post processing for DSM

In this step, these areas with no-data value in the above mosaicked DSM are interpolated, and outliers (or small spots of errors) in the resultant DSM after interpolation are removed. The output of this step is the product of dense DSM, which is generated by this software. The DSM product can be used in the different applications followed.

By clicking the command item, Post Processing, in the above menu, the GUI program is launched. The graphical interface of the program is as follows:

The concept of work directory is the same as that in stereo matching and DSM generation. All files required in the course of ortho-rectification should be put in the work directory. In the section of input files in this interface, the file of interior parameters of camera and the list file of exterior elements are the same as those in the step of stereo matching and DSM generation. Thus, the directory, I:\points\images, is still set as the work directory in this step.

All options before the option, Format of each resultant ortho image, are the same as those in the step of stereo matching and DSM generation. Format of each resultant ortho image: the file format can be configured. The formats, such as GTiff and ERDAS IMAGINE (.img), can be used.

File of elevation source: the full file path of the external elevation source used in the ortho-rectification. The result in Step 2, post processing for DSM, is selected as the elevation source. The coordinate system of elevation file must be the same as that of exterior elements and the elevation file covers all the areas of these images. If third party elevation source is used, please make sure the sameness of coordinate system. Resolution: the image resolution (Unit: m) of the ortho-rectified image. The resolution of ortho-rectified image can not be better than the actual GSD (ground spacing distance). Ratios deleted in the X end and the Y end: the ratios need to be deleted in the two ends for X, Y directions, respectively. The remained center part of ortho-rectified image after deleted in ends is a portion with high quality.

Number of used threads: setting the number of used threads (CPU cores or the virtual CPU cores by using hyper-threading technology). For the cases where CPU cores are enough, we suggest that number of 4, 6 or 8 is set here.

After the above options in the interface are set, users can click “Save Configuration” to save these options. These configuration options will be saved in a configuration file, aerialOrtho.conf, and next time the options can be loaded from the configuration file by clicking “Load Configuration”. The configuration file, aerialOrtho.conf, is also stored in the work directory. If the button of “Execute” is clicked, the configuration file will also be generated in the same way.

In the output setting, users should set the output directory and the filename of the ortho-mosaicked image. In the output directory, the ortho-rectified image for each image will be stored. The resultant images after ortho-rectification are named in a specific rule: image ID_ortho.extension. The data type of ortho-rectified images, as well as the number of bands, is the same as that of original images, e.g., unsigned 8 for original image, still unsigned 8 for ortho-rectified image. The file format of resultant images is set in the configuration option “Format of each resultant ortho image”. The output ortho-mosaicked image should also be stored in the output directory.

No-data value in the output setting is the value used to fill in the area without intensity value (area with no-data value) in the resultant ortho-image. The value is also called as invalid value or background value.

After finishing the setting of configuration options, input and output setting, users can click the button of “Execute”. The called program, aerialOrtho.exe, starts to run and the required time to finish the whole procedure is different according to the size of the aerial block. In the course of computation, the buttons of “Execute” and “Cancel” on the bottom of the form is invalid. The two buttons can not be clicked in case they are clicked many times in the course of running. Users can learn the progress and the running status via the re-directed output printing (sometime printing may delay) on the right side. User can also check the information of resources (CPU, memory and Disks) possessed by the program from Task Manager and Resource Monitor of Windows OS. Once the execution of aerialOrtho.exe is finished, a message box will pop up showing that the processing is closed successfully or terminated (aborted). After clicking OK button on the message box, the GUI program returns to the available status. Users can either click the button of “Cancel” on the bottom or click the closing icon on the up-right corner of the interface to close this GUI program. Or users can select and set new input and output to fulfill a new task.

User can click the button of “Terminate” on the bottom if they need to abort the processing (not the closing of GUI form). The GUI program, aerialOrthoForm.exe, will kill the process of aerialOrtho.exe which is being called. Killing the process of aerialOrtho.exe may delay (less than one second or several seconds). Once the process is killed, a message box will pop up showing that the processing is terminated (aborted) or closed successfully. After clicking OK button on the message box, the GUI program returns to the available status. Users can either click the button of “Cancel” on the bottom or click the closing icon on the up-right corner of the interface to close this GUI program. Or users can select and set new input and output to fulfill a new task.

Attention: the button of “Cancel” on the bottom is only for closing the GUI program. If the called logical program (i.e., aerialOrtho.exe) is running, users should first click the button of “Terminate” to abort the processing task or wait until the processing task is finished, and then close the GUI program. Users can not click the button of “Cancel” or click the closing icon on the up-right corner of the interface to close this GUI program when the called logical program is running.

The blank area of the right side will display the information printed by the command program, and the printed information will also be saved in a log file named as aerialOrtho_ddMMMyyyyHHmmss_log.txt. In the filename, dd are two digital numbers indicating a date, MMM are three English characters indicating an abbreviation of a month, yyyy are four digital numbers indicating a year, and HHmmss are digital numbers indicating hour, minute and second in the form of 24 hours. The log file is also stored in the work directory.

All configuration options are saved in the configuration file, aerialOrtho.conf, through a certain type of form in the course of running of program. The configuration file can be used in the action of loading configuration.

At the same time, a list file named ortho_List.txt is generated, which is saved in the output directory. The list file includes, in sequence, all filenames of ortho-rectified images whose order is the same as that in the list of exterior elements of images. The format of the list is as follows:

I:\points\images\TDOM\01_ortho.tif

I:\points\images\TDOM\02_ortho.tif

I:\points\images\TDOM\03_ortho.tif

I:\points\images\TDOM\04_ortho.tif

I:\points\images\TDOM\05_ortho.tif

I:\points\images\TDOM\06_ortho.tif

….

Step 4: Comparing surface height and change finding

By comparing DSMs of two different phases, the program can automatically find change of the surface height and calculate the value of changed height. Clicking the icon showing “Surface Change” in the main interface,

The operating interface of change of surface height is launched.

The corresponding DSM files are selected in the sections of the previous DSM and the next DSM, respectively. After processing, the file of height difference is obtained. Users can set two parameters, the height threshold and no-data value.

The height threshold: If the height difference is less than the threshold, the difference is not interesting and it will be assigned as no-data value in the resultant file. For the case where the height difference is more than the threshold, the real difference will saved in the resultant file.

No-data: no-data is the value used to fill in the area without change of surface height (or invalid area) in the resultant file. No-data can be determined either from input DSM or from the right side list box.

Step 5: Automatic DSM2DTM

Clicking the icon showing “DSM to DTM” in the main interface,

The operating interface of automatic DSM2DTM is launched.

The program adopts an algorithm with multilevel triangle-based ground filtering. It deletes the non-grounded objects like buildings, trees in DSM and transforms the DSM to DTM where the pure ground height is saved. The input file is DSM source and the output file is resultant DTM.

The meaning of parameters is as follows:

The predefined size: the defined size in which the lowest point is selected as a ground point; unit: the same as the grid spacing (cell size), e.g., 40.0. It means that the lowest point in a grid, whose sizes of width and height are both 40 meters (assuming the unit of grid spacing is meter), is taken as a ground point. The higher is the predefined size, the more levels in the pyramids are generated. Level number of pyramids decrease, then the built triangles is to be dense. This parameter is usually decided by the size of the biggest non-ground object in the terrain area. If the predefined size is less than the size of non-ground object, these objects will not be filtered out. On the contrary, if the predefined size is too large to maintain some terrain details. Thus, users need find a balance between filtering out big non-ground objects and maintaining the terrain details in the light of the requirements of applications.

Level, to which level the DSM is filtered. The higher is the level set, the less ground points are generated, the less terrain details remain, and the more efficient is the processing. The lower is the level set, the more ground points are generated, the more terrain details remain, and the less efficient is the processing. Usually the triangulation of mass points and searching a specific triangle in a huge triangulation is inefficient. The level set can not be higher than (the highest level - 1), level is 0-based, e.g., 3.

The threshold of distance: the threshold of distance from a point to the corresponding triangle. In the course of filtering, a point whose distance to its corresponding triangle is more than the threshold is deemed as a non-ground point, vice versa, e.g., 1.0 meter. If the value of threshold is low, there are less ground points which will survive in the filtering processing and there are also some risks that the true ground point may be filtered out by taking them as non-ground points.

The size of block: for processing large raster, block division is needed. Filtering is fulfilled, block by block, and its size must bigger than two times of overlapping size, e.g., 6144. Usually the default value is used. The reason that block division is used is that a large DSM will result in huge ground points which require huge computation for the filtering processing. The block division is a way which promotes computational efficiency and saves memory consumption.

The size of overlap between blocks: the size of overlap between the adjacent blocks, e.g. 128. The overlay ensures the rightness of border of each block. Usually the default value is used.

No-data: no-data is the value used to fill in the area without height value. Because each grid in raster file must be assigned a value, for some cases where there are no real height values in some areas, the concept of no-data is introduced. No-data can be determined either from input DSM or from the right side list box in this interface.

If there are some non-ground objects which are not filtered out, such as buildings and vegetation areas, or small areas of errors in the resultant DTM in this step, the interactive tool for editing DSM/DEM (i.e., collectPolygons.exe) can be used for editing. For more details, please refer to “Usage of the collectPolygons.exe program”.

Step 6: Height estimation of building / tree

Clicking the icon showing “Building height” in the main interface,

The operating interface of height estimation of building / tree is launched.

The corresponding files are selected in the sections of the ground height (DTM) and the surface height (DSM), respectively. After processing, the file of building / tree height is obtained. Users can set two parameters, the height threshold and no-data value.

The height threshold: the height being less than the threshold is the value which is not interesting or the possible existing errors. The value will be replaced by no-data in the file of building / tree height. The height being more than the threshold is an interesting and reliable value, which as a true value will be saved in the file of building / tree height.

No-data: no-data is the value used to fill in the area without building / tree (or invalid area) in the resultant file. No-data can be determined either from input DSM or from the right side list box.

Step 7: Applications

Clicking the icon showing “App” in the main interface,

The following menu will pop up.

Currently two applications modules are included, i.e., volume calculation and automatic extraction of building attributes in the light of buildings footprints.

Volume calculation: a polygon in the vector form in which volume is calculated and highly dense DSM are given, the module estimates the volume of objects (e.g., sands, small stones, coal, mineral particles and garbage) occupying the area. For more details, please refer to “Usage of the calVolume.exe and calVolumeForm.exe programs”. Users can click the command item, Polygons Drawing Tool, in above menu to launch the interactive tool, collectPolygons.exe, to collect the polygon and save it.

Automatic extraction of building attributes: a vector file with ERSI shape format, which including multiple polygons of building footprint, and the corresponding nDSM dataset are given, the module automatically extracts the center position (x, y coordinates) of building, area of ground, height of building, number of layers, and construction area of building for each building. Moreover, these extracted values are set as new attributes for these polygons. nDSM can either be obtained by subtracting DTM from DSM in the module of buildingHeightForm.exe, or be obtained by calculating difference between two DSMs in the module of surfaceChangeForm.exe. The former can be used to extract building height from the bottom to top, number of layers, etc., while the latter can be used to automatically find new, illegal, added, demolished, or height-exceeded buildings and extract their attributes, such as position, height, layers, ground area, and construction area of these found buildings. For more details, please refer to “Usage of the extBldgAttributes.exe and extBldgAttributesForm.exe programs”. Users can click the command item, Polygons Drawing Tool, in above menu to launch the interactive tool, collectPolygons.exe, to collect polygons on nDSM and save them to a vector file. Polygons of building footprint in vector file can also be from third party source. For both cases, it is required that building footprints are accurately aligned with the actual boundaries of buildings. And, the vector file including polygons and the nDSM file should be geo-coded and the underlying coordinate system is the same.

Step 8: 3D modeling with true color textures

Clicking the icon showing “Textured 3D Model” in the main interface,

The following menu will pop up.

By clicking the command item, textured 3D modeling, the GUI program is launched as follows:

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