# Calculating volumes of gravel piles

2»

edited November 2013
Basically what the special Pile Volume option does is sample the terrain along the area boundary, then creates a surface by triangulating those points and sampling it inside the boundary. So if the boundary is around the base of the pile that should be a flat-ish surface that can then be subtracted from the full surface with the pile to get the pile volume. If you are on a slope this should also work as the surface to subtract will just also be sloped. So the important thing is that the pile area goes around the base of the pile.

Of course if you have 2 surfaces to start with, one with pile and one without that will be more accurate, but since that often isn't available this method will get you close enough without needing old and new terrain/Lidar.

Thanks,

Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
• Global Mapper User Posts: 33Trusted User
edited November 2013
Basically what the special Pile Volume option does is sample the terrain along the area boundary, then creates a surface by triangulating those points and sampling it inside the boundary. So if the boundary is around the base of the pile that should be a flat-ish surface that can then be subtracted from the full surface with the pile to get the pile volume. If you are on a slope this should also work as the surface to subtract will just also be sloped. So the important thing is that the pile area goes around the base of the pile.

Of course if you have 2 surfaces to start with, one with pile and one without that will be more accurate, but since that often isn't available this method will get you close enough without needing old and new terrain/Lidar.

Thanks,

Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation

What if you had only one surface with the pile and no surface to compare? How would one do it with the "Measure Volume between Surfaces" option?

I tried the following...

1) Exported the Surface (tiff) to a LAS file.
2) On the LAS file I made a polygon around the pile with the digitizer and deleted the points.
3) Tried generating Elevation Grid from 3D Data... BUT

Global Mapper instead of sampling the points around the pile and completing the surface, it leaves the "white polygon" (where I deleted the points) so that area doesn't have any elevation data. The option was set to "Tight".

3b) Exported the LAS back to a surface (tiff).
4) When I used the "Measure volume between surfaces option" the results are not real.I get like 6 m3 instead of 4,200 m3. So the option is not taking in consideration the area with no elevation data (the pole, where I deleted the points).

Does what happened in 3a a bug or its just working as intended? I mean, I'm supposed to be able to delete points and regenerate the surface and the software should sample the area where I deleted the points with data around the area.

Excellent customer service.
edited November 2013
You want the setting set towards 'Loose' when regenerating the terrain. If you have it near Tight then anything not very close to a sample if treated as invalid and as you've noted if there's no elevation no volume difference is calculated there. The Loose setting will fill the gaps. This is basically what the Pile Volume option does internally, or the option on the Measure Volume dialog when doing an area measurement to Use Base Heights from Terrain Surface (this is what the Pile Volume shortcut just does automatically).

Thanks,

Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
• Global Mapper User Posts: 33Trusted User
edited November 2013
You want the setting set towards 'Loose' when regenerating the terrain. If you have it near Tight then anything not very close to a sample if treated as invalid and as you've noted if there's no elevation no volume difference is calculated there. The Loose setting will fill the gaps. This is basically what the Pile Volume option does internally, or the option on the Measure Volume dialog when doing an area measurement to Use Base Heights from Terrain Surface (this is what the Pile Volume shortcut just does automatically).

Thanks,

Mike
Global Mapper Guru
geohelp@bluemarblegeo.com
Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation

It worked! Now I just need to add points to that area so the surface doesn't looks so flat.

Thanks!
• Global Mapper User Posts: 33Trusted User
edited November 2013
Now I only have one last question:

Oh the area where I deleted the points. How do I make the terrain look more "real". Since there's no data in there, I don't know if I can trust the accuracy of the surface generated over the "hole". It looks like this.

image (3).png

Is there any way to achieve that? Like if I can interpolate using data from the neighborhood of the surface? Anything?