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Apply Helmert's or Least Squares Transformation to a point cloud

  • 1.  Apply Helmert's or Least Squares Transformation to a point cloud

    Posted 04-04-2022 11:30
    Edited by Carter Matte 12-12-2023 03:17

    Hi,

    I am trying to use the "Transform Survey Points" tool under the Survey ribbon to apply a least squares or helmert's transformation to a point cloud. After selecting the point cloud, determining the transformation, and applying the transformation to the point cloud the point cloud is still remaining in the same place. 

    I have tried using the "Georeferencing Tool" under the Point Cloud ribbon however the results are inaccurate. I need to apply a calculated transformation however haven't had any results when applying it. 

    Anyone else have any experience with this?

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    Ben Vallieres
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  • 2.  RE: Apply Helmert's or Least Squares Transformation to a point cloud

    Posted 04-04-2022 17:42
    Where is the point cloud from? If it's SX10 data then you can use Transform Survey Points. However instead of applying the transformation to the point cloud directly it should be applied to the survey point where the SX10 was setup. If you transform these point then the point cloud will move with them.
    However if it's laser scanner data (TX8, X7, etc) or an imported point cloud then Geo referencing is probably the best option.

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    James McWha
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  • 3.  RE: Apply Helmert's or Least Squares Transformation to a point cloud

    Posted 04-05-2022 05:13
    It is a rigid point cloud derived from DJI Terra. The payload used was DJI's L1 sensor. I am finding the scan registration and georeferencing commands to be dismal with rigid point clouds.

    There is not much explanation as to what the Georeferencing tool is actually doing, nor is there any reporting as to what transformation was applied using this tool. As i said the results of this method are yeilding accuracies which we can not accept. We need a calculated transformation. 

    Are there any Rotate, Transform and Scale commands for rigid point clouds?

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    Ben Vallieres
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  • 4.  RE: Apply Helmert's or Least Squares Transformation to a point cloud

    Posted 04-05-2022 14:10
      |   view attached
    These inaccuracies are most likely due to grid to ground scaling issues between our coordinate system and point cloud. Please have a look at the following webinar for more details:

    https://go2.trimble.com/2020-07-GEO-WB-TBCPH_LandingPage-Replay.html?_ga=2.264385103.1955609884.1649038179-980793681.1612901581

    Also attached is a White Paper on the subject.


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    James McWha
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