Global Mapper v25.0

Is it possible to get a straight/vertical side when creating embankments?

I tried to add this using "Ask a question" but kept getting an error page, so apologies if this is a discussion.

Essentially, I'm trying to rebuild an old industrial landscape, and am putting back in place, bridge embankments that where removed when the bridges in question where demolished.

I'm managing to do this ok using the flatten site plan tools, however, there is one small challenge I'm facing.

Take the following image:

The north most embankment I created using a center line which I then aligned to the required slope and buffered it. The south most embankment, I drew by hand and set the per vertex elevations from manual calculations as required.

The inner gap however (IE: the space under the bridge) the embankment side was vertical.

In essence, the sides of the embankment shown with green lines, should be a drop straight to the elevation below.

Is there anyway I can achieve this with the normal workflow for creating flattened site plans from polygon geometry, or if not, what would be the quickest way to make them vertical after the embankment has been created using other tools.

Many thanks in advance for any pointers.


  • HI Winirek,

    There is no way (that I know of at least!) that you can do what you are asking directly in GM i.e. in one step.

    The workaround that I use when modelling complex shapes/surfaces in GM is to "build up" multiple terrains or surfaces and combine them using the "Combine Terrain Surfaces" BEFORE creating the required design surfaces using the "Flatten Site Plan" tool.

    So in your example above, what I'd do is "add" the vertical retaining walls (create "glass" walls 100 m high x 500 m high say) and then combine it with your underlying topography using the "Combine Terrain Surfaces". Then I'd create your embankments as you have done above, but being sure to use your new combined topography. Once you have the 3D embankment surfaces that you require i.e. with the vertical walls you can remove your modified topography and re-use your original topo.

    I hope I have explained that clearly. If you want to clip that part of your model out and upload it as a zipped GM Package file I'd be happy to show you exactly what I mean.



  • Sorry that should be (create "glass" walls 100 m high x 500 m LONG high say) above...

  • I just though of a much simpler workaround although its a bit of a cheat... It won't be super-crisp in 3D, but if you only need planar/orthogonal views it could work for you.

    Why don't you create a box or closed polygon around each of your bridge embankments with one edge of the polygon aligned with the vertical retaining wall and then crop to each of them as per attached screen grabs?



  • Hi @CarrickCon ,

    That second way of working might be better now that I think about it, esp in the particular bridge that I'm working with, as it actually has 2 90 deg straight sides.

    The red edges show the 2 sides/parts that need to be vertical, image below shows the whole bridge.

    So I think some creative cutting with a polygon as per your suggestion no 2 may actually be the best way forward, I'll have a play with your suggestions over the next few days however and see how I get on.

    Ultimately what I need to produce is a one piece height map that will be loaded into a game engine, which will then allow a viewer to walk around the landscape, populated with buildings, railway lines etc in a VR headset.

    I'll let you know how I get on.


  • @CarrickCon , just wanted to let you know that the "Cropping method has worked a treat.

    I've now got a whole new work flow, where I use a poly to build the bridge pier, then a line from the new height to the point on the road that equals the old height, I use that line to generate a profile and find the slope.

    I then draw a poly around the bridge pier, making sure I cut off the bits I want straight, followed by cropping the pier using that polygon. Then I generate the embankment polygon, set it's slope to the slope from the line profile, or I buffer the line, whichever is the best for the area.

    Finally I generate the site flattened area for the embankment, and then get rid of all the polygons.

    Final result

    Which is exactly what I need.

    I am interested in a little more detail in your "glass wall" approach however, I couldn't quite fully figure out your steps for that one, but I learned a few new things trying.

    Thanks for the assist.

  • Hi @Winirek.

    I'm glad that you found the cropping tip useful. I think that we often forget that cropping can be used not only to crop images/rasters, but also 3D surfaces and that has got me out of a few jams in the past...

    I've tried to explain what I was saying above about the "glass wall" and combining surfaces in the following plan and profiles shown on the screengrabs below.

    Screenshot 1 - Topo + 2D linework:

    Screenshot 2 - Topo + "Glass/Hypothetical" Retaining wall to 550 mRL:

    Screenshot 3 - Combine Original Topo + "Glass/Hypothetical" Retaining wall (combine using "maximum" elevation) to make single combined surface:

    Screenshot 4 - Combined Topo + Road Embankment:

    Screenshot 5 - Original Topo + Road Embankment (turn off combined topo and turn original topo back on):

    I hope this helps, please get back to me if still unclear. I use this approach of creating "hypothetical" surfaces and building up the earthworks design in stages as that is what often happens in the real world of civil engineering with temporary retaining structures or falsework...



  • @CarrickCon ahhhh, right I think I get a better idea now. I'll play more over the weekend.

    "I'm glad that you found the cropping tip useful. I think that we often forget that cropping can be used not only to crop images/rasters, but also 3D surfaces and that has got me out of a few jams in the past..."

    Yes indeed, it's the same in my day job profession as a software developer. We often overlook the simple solutions in favour of a more complex or longer work-round, I think often it's because we feel that something that took a lot to achieve must be better and more robust, but quite often that's not the case.

    Going back to the cropping method, after I posted last night, I actually worked out that I could actually "cut out" holes using the cropping method, so now instead of lots of complex shapes to define the embankment, pillars and slope lines, I just draw one complete slope line, set the heights as needed, render the embankment, then cut out the gaps for the bridges.

    I get the same great results, and an even simpler workflow.