Global Mapper v24.0

Is there a way to sink a ditch/furrow with a trapezoidal cross section following a line in a DEM?

mcb9060 Global Mapper UserTrusted User
Hi, I have a DEM with 25cm resolution and I would like to sink a ditch/furrow into the DEM. The ditch has a trapezoidal cross section, each side of the ditch has 2 different angles of slope. I already have a line representing an existing pipline and I want to sink the ditch into the terrain along the existing pipeline. I need to be able to define the slope, depth, width of ditch etc. I see the Terrain Painting tool has something approaching what I want except I would like to select an existing line and not digitise with the "brush" and also I need to be able to define the dimentions of the ditch. I am using Global Mapper v22.1.1. Thanks very much. Mark


  • Hi mcb9060, the simple answer is yes what you ask can be done easily within GM. I use GM frequently to do develop 3D earthwork designs for roads, channels, embankments, bunds, pits, waste rock dumps etc. 

    I suggest that you spend 59 minutes of your time reviewing this excellent webinar "Working with Terrain Data in GM":  http://https//  If you can't afford 59 minutes, watch from about minute 34 onwards. This webinar is excellent and even though its based on an old version of GM (V16) the principles and most of the dialogue boxes are exactly the same in current V22.

    The workflow that I would adopt to do what you request would BRIEFLY be as follows (you will find Buffer tool and Calculate Flattened Site Plan tool under Advanced Feature Creation Options menu - you need to get familiar with this menu - its  very powerful!):
    1. Construct centreline along your ditch
    2. Edit vertex elevations to the design you require
    3. Buffer the centreline to form base of ditch. Normally if the trapezoidal ditch had equal side slopes I would buffer both sides equally, but as you need uneven side slopes you will need to buffer to LHS and then to RHS.
    4. Selecting LHS buffer shape then select Calculate Flattened Site Plan and apply the side slope you require.
    5. Do same for RHS.
    6. Combine both halves of ditch using Combine/Compare Terrain Layers under Analysis menu. Select "Minimum" for your operator as the ditch is cut into existing surface (if it was an above ground embankment say, you would select Maximum operator). 
    7. You are done! You can compare final surface with original to get cut volume. You can cut cross-sections to view ditch dimensions. You can contour and export as dxf or dwg if you want to bring into AutoCAD etc.

    Sorry, if I had more time I would explain in more detail... Basically get to know Advanced Feature Creation Options menu and Combine/Compare Terrain Layers under Analysis menu and you will be home and hosed... ;)


  • Hi mcb9060, 

    Sorry I pasted an extra http into link above!

    Try this: 


  • mcb9060
    mcb9060 Global Mapper User Trusted User
    Hi CarrickCon, thanks very much for your comprehensive response to my query. I will have a look at that technique. Global Mapper has a great number of tools and options that require experimenting with. Thanks again. Best wishes, Mark
  • Stick with it Mark - as a one man band engineering consultant I use it all the time for 3D design of civil/mining earthworks and have saved a fortune in contract drafting services! I do the 3 modelling in GM and then export it as dxf into AutoCAD to produce contract drawings.

    If you have high quality DEM data then you can produce highly accurate models in GM no problem. I've attached a few screengrabs of recent designs for mine site haul roads...