"Unable to grid 3D points from selected overlays."

James Cox

Hi,

I'm trying to use the Global Mapper SDK to create a GeoTIFF from several layers of elevation data.
I've noticed that depending on the resolution that I pass into my GM_GridGenSetup_t object, I will sometimes get this error after calling GM_GenerateElevationGrid().

The full error information that I get is:
Unable to grid 3D points from selected overlays. Access is denied. MemoryMappedFile.cpp - 403

It appears to happen when I pass in a very coarse resolution. For example if I set my GM_GridGenSetup_t object's mXRes and mYRes to 0.5 pixels per meter, I get no error. But if I pass in say 0.05 pixels per meter, then I get the error as described.

global_mapper

You are likely specifying a grid size that is too large to fit in a temp file in your temp folder. When a grid is large is spills to a temp file on disk, if you run out of disk space where that file is being placed you will get an error. How much space is on the drive that has your temp folder?

Thanks,

Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com

James Cox

Hi Mike,

Thanks for the reply. The drive does only have a gig or so free so that might be the issue.
Is the resolution passed into the GM_GridGenSetup_t object a pixels per unit or a units per pixel measurement?
As I mentioned 0.5 works but 0.25 does not.

Thanks,
James

global_mapper

James,

It's a "units per pixel" measurement, so 0.25 would create twice the resolution and require 4 times the storage.

Thanks,

Mike
Global Mapper Guru
gmsupport@bluemarblegeo.com
http://www.globalmapper.com

James Cox

Thanks Mike, that clears up very neatly some long-held assumptions that were absolutely wrong.