Editing DEM

rapidrapid Global Mapper UserPosts: 3
edited May 2015 in Elevation Data
Hello, someone recommended GM as a possible tool for my intended application.
I have a DEM generated from photogrammetry package, as it is, the DEM also include cars, shrubs, small buildings etc. on it.
Can someone describe a workflow for me to edit these 'anomalies' in the DEM out in GM and come up with a good clean DEM (as natural surface as possible)?

p.s I'm not a GM user yet, so please use general terms..



  • stihlstihl Global Mapper User Posts: 52Trusted User
    edited May 2015
    You're mixing up some geodetic terms.
    What you have is a DEM and what you want is a DTM. From an elevation model to a terrain model by filtering out all the unwanted non-ground points.
    I'm not aware of any failproof automated way of doing this. The automatic ground classifcation doesn't always work well so it's usually a manual job.

    First you should make a polygon around the entire model, this can be done easily by right clicking on the DEM on the layer list and selecting 'BBOX/COVERAGES' and select the 'Polygonal coverage area'. This should auto calculate a polygon around the entire dataset.
    Next you'll have to make 'Area features' around the objects (cars/trees etc etc) that you don't want.
    Once you're finished with that, simply select all of the small area features, right click anywhere on workscreen and go to 'Crop/Combine/Split functions' and click on 'Cut selected areas from another area'. Then left click onto your model, and thus selecting the outline you've made before, to select the other area it should cut the features from.

    Now you should end up with your DEM with an outline that has holes of where all the objects like cars etc are. Now you can export this DEM while cropped outline. I usually export the model as LAZ, then reimport that back and regenerate a 3D grid from that as I let it interpolate. That will leave you with a Digital Terrain Model or DTM, linearly interpolated of where all the unwanted objects used to be.
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