Global Mapper Pro

Combine photogrammetric and lidar point cloud

Hello,


I capture my raw data with a DJI L1 and get Lidar as well as multispectral outputs from it on the one hand. I create both, a Lidar point cloud and a photogrammetric point cloud. With my Lidar point cloud there are always errors in the overlap areas of my flight swaths. This results in height differences of up to 30 centimeters. To avoid this error, I would like to access the points of the photogrammetric point cloud at these locations. I am currently testing these considerations on a small section and am not getting a good result, however. I use the tool "Fit Point Clouds". My two point clouds consist of 120,000,000 points. There are about 1400 points per square meter and the point spacing is 0.02641 meters. Possibly there is another way to solve this problem or a tool to improve my flight strips of the Lidar point cloud. I would be grateful for any idea and support. Two screenshots are attached to visualize my problem.


Best regards,


Schsan


That is a profile of my Lidar Pointcloud. You can see the height difference as well as a gap in the middle of the strip.


The gray stripe shows the point cloud of the photogrammetric data evaluation. It is a straight, stable point strip.

Answers

  • 30cm delta between your photogrammetry and lidar point clouds is a problem that needs to be solved BEFORE you get to the point of combining them in Global Mapper. That's a significant misalignment.


    If you're using the DJI L1, I'm assuming you're running it with RTK and (possibly) not using any ground control targets at all? If that's true, the first step would be adding some ground control targets with surveyed coordinates and using those control points to adjust both your photogrammetric and lidar datasets during processing.

    If, for whatever reason, that's not possible - Use your highest-confidence dataset to extract common tie points, then use those tie points to control your 2nd project (Ex: Extract the XYZ coordinates from identifiable features, such as roadway striping or sidewalks, from the photogrammetry dataset and then hold those as control to adjust the lidar dataset).

    Once both of your datasets are aligned with common control points (and done so in the programs you used to process the raw data), then you can bring them into Global Mapper and start to pick and choose where you merge them.

  • For what it's worth, the recommendation above really isn't an ideal workflow either, if precision is your primary objective. There's really no getting around the fact that you need survey-grade ground targets in every project (even when the salesmen tell you otherwise). Even in the rare situations that a high level if precision -is- possible without ground control targets....you need a way to verify that you're achieving the accuracy you think you're achieving.

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