Global Mapper v25.0

DEM from LiDAR capture

Hi all, I'm having trouble getting slope mapping that I can make sense of from a DEM LiDAR capture. I've worked with slope mapping a fair bit, however when I generate it for the DEM I have been provided areas that are flat appear to have an very uneven topography. Should the DEM be smoothed somehow?

When I use the gradient shader it appears pretty good:

However when I use a custom gradient shader with 'excessive' slope areas shown in red there's flecks of red through everything.

I feel like I'm missing something here. Any help would be appreciated. I can share a Dropbox link to the source data if that helps.


  • bmg_mike
    bmg_mike Global Mapper Guru Moderator, Trusted User

    I believe the issue is due to the very high resolution of Lidar scans causing local slope to look quite large and variable, even though the slopes are over tiny distances. For example, think of a surface covered with gravel rocks. It may be quite flat at a large scale, but for a detailed Lidar scan where every little rock is captures, you will have lots of high slope over mm to cm scale that evens out to a flat surface.

    What I would suggest is gridding your Lidar using the Bin Average (or maybe Bin Minimum for DTMs) with a very large bin size, at least 1m on a side. Then any small-scale variance will be smoothed out and you will get a slope that is more akin to what you are after.



    Global Mapper Guru