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Getting building height from subtraction

kentman
kentman Global Mapper UserTrusted User
edited March 2013 in Elevation Data
I have two files (DSM & DTM) and would like to subtract the DTM from the DSM to give me a new z value which would equal the height of the buildings - both files have the same points in the same locations. How do I achieve this?
I have both .asc and .xyz formats I can use.

I would also like to average the z values for a number of polygons and then extrude them by that value - is this possible?

TIA Kent

Comments

  • global_mapper
    global_mapper Administrator
    edited April 2012
    Kent,

    You could create grids from each file then use the File->Combine Terrains menu command to subtract the 2 surfaces. Once you have the subtraction surface, you can select the polygons of interest with the Digitizer Tool, then right-click and select the option to calculate elevation statistics for the areas to get things like the average Z values added as attributes to the areas. Then go to the Options dialog for the layer those areas are in and choose to use the AVG_ELEV attribute as the elevation, then you can extrude those areas based on that in the 3D viewer.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • kentman
    kentman Global Mapper User Trusted User
    edited April 2012
    Kent,

    You could create grids from each file
    Do you mean by this to export a grid as they are in this format anyway?
  • global_mapper
    global_mapper Administrator
    edited April 2012
    Sorry I thought you were loading them as 3D points for some reason. If you already have the grids, just load them up, then use File->Combine Terrains to generate the difference surface.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • Baha
    Baha Global Mapper User
    edited March 2013
    Dear GM Guru Mike,
    I've searched all threads and wasn't able to find an answer. If I have DSM and DTM, as well as shape (polygon) objects. Is that possible in GM to assign average/min/max differences of DSM and DTM to the polygons's attributes overlaying that area?
    Thanks a lot and I appreciate your response!
    Baha
  • global_mapper
    global_mapper Administrator
    edited March 2013
    Baha,

    If you first use the Analysis menu command to Combine/Compare Terrain you can great a new grid layer that is the difference between the 2 grid surfaces. Then you can select the area features with the Digitizer Tool and right-click and select the Analysis submenu command to calculate elevation statistics for each area. Then you will have the attributes that you want.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.bluemarblegeo.com/products/global-mapper.php
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