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path profile with Lidar point cloud?

SMcQSMcQ Global Mapper UserPosts: 24
edited April 2011 in Technical Support
Can Global Mapper create a path profile from lidar point cloud data? In particular, can it show colors assigned to the points by merger with multi-spectral data and render these colored points in profile?

Thanks.

SMcQ

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2011
    Currently you have to create a gridded terrain layer from the point cloud data, then you can create a path profile over that. The colors won't come from the colored points. However, we are planning on adding an option to create a colored path profile directly from Lidar point cloud data in a future release, so hopefully you will soon have this capability!

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • SMcQSMcQ Global Mapper User Posts: 24
    edited April 2011
    Thank you for your reply. It is encouraging that you are considering a profile feature for color coded point clouds.

    Not knowing much about the programming required, I was thinking about what an algorithm could do in order to capture something useful from a point cloud profile.

    For instance, because we are dealing with points, the path of the profile has to have some thickness in order to capture enough points to show a cluster representing an object. But the thickness might not show the whole object thus intersected. It would be most helpful if the points in a cluster could all collapse to the profile regardless of the thickness of the capture zone.

    Trees are meaningful in profile only if the whole silhouette is shown, in other words, all the points in the sub-cloud defining the tree. If the capture is limited to a thickness of the profile then only a slice of the tree is shown, which creates a misleading impression of the full tree canopy.

    Imagine a bunch of cylinders of various sizes distributed on a surface, and an orthogonal profile plane that intersects some of the cylinders. If the profile plane has a thickness of capture, the intersected cylinders are projected to the plane only for their captured volume, and are thus misrepresented in diameter on the profile plane.

    But if the algorithm had a way to define the whole cylinder, the plane passing through any portion of it would capture the whole volume of the cylinder and project it upon the profile plane. Thus, the profile would represent the silhouette of the cylinder.

    As with the solid volume example above, so with a point cloud. Of course, you also need some way to exclude overlapping silhouettes as determined by the user. This could be based on proximity to the profile plane, within a user determined tolerance.

    This is computationally more intensive than a simple Boolean capture set, but a lot more useful. Tree silhouettes can actually be used to verify their hyperspectral identification, as different tree species have distinctive profiles.

    SMcQ
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2011
    Thank you for your thoughts. I agree there will likely be some tweaking to be done with this operation is implemented in order to extract the most useful information from the point cloud. I imagine the more useful properties will become apparent once implemented in practice.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • SMcQSMcQ Global Mapper User Posts: 24
    edited April 2011
    The Lake Tahoe Lidar set has just been posted on opentopography.org

    Here is an alias to the direct link: http://goo.gl/xcNyS

    Would love to see what you can do with this as it is the reason we bought Global Mapper.

    SMcQ
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2011
    You can certainly load the Lidar data from that site. I got a 500+ MB LAS file and loaded it into Global Mapper and displayed it as a point cloud. If you create an elevation grid from it then you can do a path profile. Hopefully soon the point-cloud based path profile will be available as well.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
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