Global Mapper v25.0

Calculate Flatten Site Plan Grid - Stay in the defined Polygon?

I certainly tried the search function, and never did quite find the answer I was looking for - Is there a way to flatten elevation within a polygon, and keep the specified slope within the polygon?  I even tried checking the "Flatten terrain Inside area(s) Rather than Outside" option, that gave me vertical walls around the perimeter , with the requested slope grades sloping into the poly.



  • Hi Resourceful,

    I'm sure there is a workaround, but its difficult to understand exactly what you are trying to do? Perhaps if you could share some screen captures we might be able to help.

  • Thank you for your reply, if there is a workaround Global Mapper tech support don't know about it!  Here is my problem - I use the Advanced Feature Creation Options, , then the Calculate flattened site plan grid with a 1:3 slope and fixed height and get this:

    I would like to stay within the polygon my client has drawn, so I tried checking the "Flatten to Terrain Inside Areas Rather than outside"  and get this:

    Here is the original polygon:  The first scenario has the proposed fill / flatten slopes extend into the neighbors property, as well as the ravine.  We don't want that..

    I am game for a workaround, or do I need to pull the pin on a GM 22 upgrade, or become reacquainted with QGIS, I do need a solution.

  • Hi Resourceful.

    As you've figured out the Site Flatten tool in GM is really set up for "top-down" modelling where you start with the upper surface of a drill pad, waste rock dump, road embankment etc. and then create the batter slopes down/up to topo depending on whether you are in fill or cut. (I've never found a practical use for the "Flatten to Terrain Inside Area(s) Rather than outside" tick box and not really sure why they added it - may be an historical appendage???).

    In your case you appear to be trying to model from "bottom-up" i.e. you have a polygon that you want to stay inside to avoid adjacent property, ravine etc. and are are trying to create the upper surface of the pile or pad.  I'm not sure if you can do that directly in GM and what I've done in situations like this is to create a dummy upper surface and then batter it down to make sure it stays within the polygon.  For instance if you wanted a pad that was 2 m high and you have a 3H:1V batter slope you could start with buffering/off-setting your polygon on the inside by 6 m (i.e. 2 x 3 ), or say for 4 m high offset by 12 m i.e. 4 x 3. Once you get your upper surface you batter down as before and check toe-line to make sure its still within the polygon...

    Its a pain to do, but will get you there in the end. If anybody else knows of a way to 3D model in GM from the bottom-up, I'd love to hear. 

  • Thank you CarrickCon,

    I have been working from that angle as well - placing a polygon inside the polygon while measuring to the edge based on the 3:1 slope would work if the height was constant.  The problem there is the road depicted is approximately 1202 meters ortho height, the rest of that area has constant slopes down to the ravine.  

    With trial and error I will eventually get it, but it won't be pretty or overly precise either.

    I suppose the Flatten to Inside areas would be handy for pit design or such.