Orientation Data from Point Clouds with CloudCompare

    Intro

    Rock Mapper allows the collection of coloured 3D Point Clouds using the iPad Pro's built-in LiDAR sensor and camera array. These Point Clouds can then be georeferenced right within the app and used to extract orientation data (dipdir/dip), for example for lithological contacts, faults or fracture surfaces.

    Such digital extraction of orientation data can be performed with commercially available software or with CloudCompare which is a free, open-source and multi-platform software package that has been developed for point cloud analysis and manipulation.


    ℹ️ If you are using CloudCompare on a regular basis and/or commercially, then we encourage you to support the open-source project with a donation.

    Workflow

    ℹ️ The workflow described below is for LiDAR Point Clouds, but also works for LiDAR textured meshes.

    1. Open Point Cloud

    Open CloudCompare and then choose File > Open



    Pick the [FaceID]_pointcloud.csv file that you would like to crop. You'll then see the Open Ascii File window. CloudCompare automatically detects the right columns for X/Y/Z and RGB (colour). 

    Just make sure to set Skip Lines to 1 so that the first line with column headers is excluded. Additionally, Ignorethe HEX_COLOUR column (because colour information is already coming from the RGB columns). FYI. By default CloudCompare will import the HEX_COLOUR column as type label which can lead to issues (CloudCompare might freeze). 

    Then press Apply or Apply all.





    ✋ Make sure to only use georeferenced / aligned point clouds for digital structural mapping. Orientation measurements for non-georeferenced or incorrectly aligned point clouds should not be used.


    Depending on the length of XYZ coordinates that are used in the Point Cloud, CloudCompare might ask to perform a shift. This allows CloudCompare to work more efficiently with large datasets but without loosing any data. Simply say Yes without changing any values.




    The point cloud will then be shown in CloudCompare's 3D Viewer. 




    2. Extract Orientation Data

    WORKFLOW 1: For Contacts and Faults use Fit Plane tool


    Select Point Cloud in the DB Tree and then click the Trace Polyline tool.




    Start digitising along the contact. When picking the first point you might see the Picking acceleration window popping up. Say Yes.




    Digitise the contact along the face AND a wall, floor or ceiling to allow for a good 3D exposure and proper plane fitting results.





    When done, press green tick mark in upper right corner. You will then see that a new polyline feature has been added to the DB Tree. Select it and choose Tools > Fit > Plane




    You can then see that a plane has been fitted through the polyline and a dipdir/dip value has been calculated.





    WORKFLOW 2: For Fracture Surfaces, Fracture Traces and Fold Axis use the Compass plugin


    It's a very powerful tool with a large range of digital mapping options. Please visit the CloudCompare Wiki for detailed instructions.


    ℹ️ It is NOT recommended to use the point cloud to extract orientation data for small structures. These should be measured with a geological compass directly in the field and then added as POI to the rock face photograph.
    Published