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Calculating volumes of gravel piles

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  • global_mapperglobal_mapper Administrator Posts: 17,238
    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
  • DionybellDionybell 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".

    So instead I

    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.

    Thanks in advance, again.

    Excellent customer service.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    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
  • DionybellDionybell 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!
  • DionybellDionybell 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?

    Thanks in advance.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited November 2013
    If you have an area feature for where you want to flatten you could select it with the Digitizer Tool, then right-click and select the Measure submenu command to calculate elevation statistics. Then go to Options dialog for layer with area and set the AVG_ELEV (or MIN_ELEV if you want) for the elevation. You can then select that area and under Advanced Feature Creation select to Create/Flatten Terrain and create a new flattened terrain in the area. That should be flat.

    Thanks,

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