Orthomosaic Production with Pix4D

Below is a basic workflow for orthomosaic production in Pix4D.

First, export a Pix4D DAT file from SpatialExplorer. Ensure that your final, processed and optimized trajectory is used to create the DAT file.

Then, in Pix4D:

  1. New Project

  2. Load all images

  3. Click next

  4. Import Coordinate System: Use a geodetic CRS that is the same as the post-processed trajectory’s datum (WGS84, NAD83, Etc.). Do not select your output CRS during this step.

  5. Load ‘refined positions and orientations’ from the DAT file created in SE

  6. If the entire project has multiple flights, open each .dat file with Notepad and merge them all together into one .dat. (This will keep the “80% of locations the same” message in Pix from appearing and negating the .dat import).

  7. Click next

  8. Select the units and desired output coordinate system of your project

  9. Select Maps as the output type and click next (do not start processing yet)

  10. Open ‘Processing Options’

  11. In Step 1, use full image size for keypoints. If your project has very low overlap or a very forested (or visually homogeneous) AOI, use ½ size for keypoints. This allows for easier calibration of individual events (cameras)

  12. Select the ‘calibration’ tab in Step1:

  13. Use ‘Accurate Geolocation and Orientation’ and optimize all parameters

  14. Everything else can be left default

  15. Process step 1

  16. Review the Quality report for large changes/errors in the intrinsics calculated as well as rough AOI coverage from the thumbnail of the entire ortho.

  17. Import GCP’s in the appropriate coordinate system (same as output from Pix4D)

  18. In Process -> Reoptimize

  19. After reoptimization, use the RayCloud view and select the GCP’s in the table of contents on the left of the screen

  20. Iteratively cycle through the GCP’s to ‘mark’ them in overlapping images. If the location is not visible, do not mark anything

  21. After all GCP’s are marked, run Step 2 and 3 to produce the Orthomosaic output.

  22. QC Ortho outputs

Alternate Workflow for use of point cloud to enforce geometry from the Point Cloud:

  1. After GCP marking, use Process -> Import Point Cloud for DSM generation

  2. Ensure coordinate systems match and there is no geoid or datum difference

  3. Once the point cloud is imported, uncheck Step 2 (DSM creation) and process Step 34

  4. QC Ortho Outputs

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