Getting building height from subtraction

kentman

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

global_mapper

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

global_mapper wrote: »

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

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

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

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