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Access: On the menu bar, click Process > Processing Options.... Then, in the Processing Options pop-up, click 3. DSM, Orthomosaic and Index.
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| DSM and Orthomosaic | Additional Outputs | Index Calculator |
Allows the user to change the selected processing options and output files for the additional outputs to be generated during step 3. DSM, Orthomosaic and Index. It contains two sections:
- Grid DSM: Allows the user to select a vector output file format for the digital surface model (DSM).
- Raster DTM: Allows the user to select the output file format and options for the raster digital terrain model (DTM).
- Raster DTM Resolution: Allows the user to define the spatial resolution used to generate the digital terrain model (DTM).
- Contour Lines: Allows the user to generate contour lines and to select the processing options for the contour lines.
Allows the user to select a desired vector file format to export the digital surface model (DSM) as a point cloud or grid.
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XYZ: An ASCII text file with the X, Y, Z position, and color information for each point of the Grid DSM.
- Delimiter: It defines the delimiter character of the file, used to separate the values. The drop-down list has the following options:
- Space.
- Tab.
- Comma.
- Semicolon.
- LAS: A LiDAR LAS file with X,Y,Z position and color information for each point of the Grid DSM.
- LAZ: Compressed LiDAR LAS file with X,Y,Z position and color information for each point of the Grid DSM.
- Grid Spacing [cm]: The spacing defines the distance between two 3D points in the Grid DSM and is given in centimeters. For example: a grid spacing of 100 centimeters will generate one 3D point every 100 centimeters. The default value is 100 centimeters. One DSM with the selected spacing is generated in addition to a DSM generated using the resolution selected in the DSM and Orthomosaic tab.
For more information about the file formats and the software with which these files can be opened: Pix4D outputs with other software > by output.
Note: It is possible to select more than one format to save the grid DSM in more than one format.
Note: The Grid DSM is restricted to 256 million points. If the chosen grid spacing or resolution generates more than 256 million points, then the grid sampling or resolution distance is doubled until the number of generated points does not exceed 256 million.
Allows generating the raster digital terrain model (DTM). For more information about the DTM: What is... (a densified point cloud? an orthomosaic? etc.).
Important: The option to generate the raster DTM is only available when the options Raster DSM and Merge Tiles for raster DSM are selected. For more information about the options of the raster DSM: Menu Process > Processing Options... > 3. DSM, Orthomosaic and Index > DSM and Orthomosaic.
- Merge Tiles (activated by default): Generates a single GeoTIFF file by merging the individual tiles. When this option is not selected, the merged DTM file is not generated and contour lines cannot be generated with the DTM.
Allows defining the spatial resolution used to generate the digital terrain model (DTM).
- Automatic (default): By default, the resolution is set to 5 x GSD. One can also easily change the resolution to multiples of the GSD.
- Custom: Allows to select any value higher than 5 x GSD, for the resolution of the raster DTM.
Allows generating contour lines using the raster digital surface model (DSM) or the raster digital terrain model (DTM).
For more information about contour lines: How to generate the contour lines.
Important: The option to generate the contour lines is grayed out if the option to merge the tiles of Raster DSM is disabled. For more information about the options of the Raster DSM: Menu Process > Processing Options... > 3. DSM, Orthomosaic and Index > DSM and Orthomosaic.
The following processing options can be selected:
- SHP: When this option is selected, the contour lines file are exported in .shp format.
- PDF: When this option is selected, the contour lines are exported in .pdf format.
- DXF: When this option is selected, the contour lines file are exported in .dxf format.
Note: It is possible to select more than one format in order to save the contour lines in multiple formats.
- Contour Base [units]: It defines the reference elevation from which contour lines are generated upwards and downwards. It can be in meters or in feet according to the coordinate system used.
- Elevation Interval [units]: It defines the contour line elevation interval. It can be in meters or in feet according to the coordinate system used. It can be any positive value.
Warning: The Elevation Interval must be smaller than (Maximum - Minimum) elevation of the DSM/DTM.
Note: The smaller the Interval value, the larger the size of the contour lines file and the more processing time will be needed for its generation.
Example: The Contour Base is used as a starting point for contour lines generation. Contour lines are generated, based on the selected Elevation Interval, upwards and downwards from the Contour Base.
For example, a project with an elevation between 315 and 350 meters with:
- Contour Base = 0 and Elevation Interval = 1 the first contour line will be at 315 meters, the second contour line at 316 meters and the last one at 350 meters.
- Contour Base = 0.5 and Elevation Interval = 1 the first contour line will be at 315.5 meters, the second contour line at 316.5 meters and the last one at 349.5 meters.
- Contour Base = 2 and Elevation Interval = 10 the first contour line will be at 317 meters, the second contour line at 327 meters and the last one at 347 meters.
- Resolution [units]: It defines the horizontal distance for which an elevation value is registered. The higher the Resolution value, the smoother the contour lines.
Example: If the Resolution is set to 100 cm, an elevation value will be registered every 100 cm horizontally.
- Minimum Line Size [vertices]: It defines the minimum number of vertices that a contour line can have. Lines with fewer vertices will be deleted and less noise will be produced.
Example: If the Minimum Line Size [points] is set to 20, all contour lines that have less than 20 vertices will be deleted.
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So the minimum Raster DTM Resolution is 5 times GSD. Can you explain why it is 5?
Also in the Processing Option for DTM, if I delete the number in Custom the system suggested to input a number between 5 and 10000 in unit of cm/pixel (please see the attached image). This could be misleading because you mentioned "Custom: Allows to select any value higher than 5 X GSD, for the resolution of the Raster DTM."
Thanks!
Hongyu Huang
Hi Harry,
So the minimum Raster DTM Resolution is 5 times GSD. Can you explain why it is 5?
We have investigated that if the resolution is less than 5 times GSD the outputs are too noisy and in terms of contour lines, for example, it does not give us any valuable information. As a workaround, you could assign points from High Vegetation, Building, Human Made Object group to disabled category and ran Step 3 in order to obtain DSM which actually would be your DTM with 1 x GSD.
Also in the Processing Option for DTM, if I delete the number in Custom the system suggested to input a number between 5 and 10000 in unit of cm/pixel. This could be misleading because you mentioned "Custom: Allows to select any value higher than 5 X GSD, for the resolution of the Raster DTM."
It's a good point. Not only in the Manual should be the information about 5 x GSD.
Best
Hello,
Sorry in advance for my english mistakes.
Is it possible to indicate the part of the point cloud we want use for the DSM and DTM creation ?
For example, if i want create a DTM of the ground, and only the ground (i have already classified my point cloud), can i indicate in the treatment options to use only the ground for DTM and DSM creation ?
Hi Vincent,
You will have to edit the point cloud and assign all points to disabled if you do not want to use them for DSM creation. You can have a look here: https://support.pix4d.com/hc/en-us/articles/202560499-How-to-edit-the-point-cloud-in-the-rayCloud.
Regarding the DTM, the DTM is generated based on the point cloud classification, and more specifically the points that have been assigned to the Ground and Road Surface point groups. For most of the cases, when all the terrain points are correctly assigned to these groups the DTM and the contour lines generated based on the DTM are accurate.
However, we have noticed that in some rare cases, such as high and wide buildings, the DTM might not be correctly generated even if all the points are correctly classified. Our DTM algorithm seems to be unable to smooth out such buildings. Usually, the problem is that the points at the rooftop are considered as terrain points creating an inaccurate DTM in these parts of the project area.
The workaround for these cases is to assign the building points in the Disabled point group, reprocess step 3 in order to regenerate the DSM and generate the DTM. Please note that doing this the DSM will not be accurate, but the DTM will be.
hallo, how you doing, hope all is well. I install my pixel4d software today but the third step (DSM) OF my application is not active, so can you assist on that please?
Hi, You will need to get a trial. If you are not able to get a trial directly, please reach out to our sales team. The one you are using seems to be Pix4D discovery which is a free version of our Pix4Dmapper software with some features disabled.