Cut and fill volumes

Mark GaleMark Gale Global Mapper UserPosts: 36Trusted User
edited November 2014 in Technical Support
Hi,

I'm using the measure tool to calculate cut and fill volumes for an area of complex shape (i.e. several hundred mouse clicks to define the shape). How do I save the area to allow me to reselect it for future re-measurements of the changing cut and fill volumes without having to retrace the area each time?

Thanks.

Comments

  • Andy WizmaAndy Wizma Global Mapper User Posts: 12Trusted User
    edited November 2014
    Hi Mark,
    Just use the "Create Area Feature" to make the shape you need (instead of using the Measure Tool), save the shape to whatever format you prefer.


    When you need to perform the calculation, select the shape using the Digitizer Tool, right-click, select Analysis/Measurement and then select the appropriate calculation method.


    Hope that is what you are after.
    cheers, Andy
  • Mark GaleMark Gale Global Mapper User Posts: 36Trusted User
    edited November 2014
    Thanks Andy, that is what I think I was looking for, except that I the answers using the two methods seem to be significantly different (a typical case: 2442cubic metres using that digitizer method, 2549 using the measure tool
  • Andy WizmaAndy Wizma Global Mapper User Posts: 12Trusted User
    edited November 2014
    Hi Mark,
    When you bring up the "Volume Calculation Parameters Setup" menu, are you choosing the same option under "Volume Calculation Type" for both methods, i.e. "Calculate Cut-and-Fill Volumes within Area Feature"?


    I've done some quick tests on one of my elevation sets and am getting the same volumes for both methods, so not 100% sure what is happening in your case.


    cheers
  • Mark GaleMark Gale Global Mapper User Posts: 36Trusted User
    edited November 2014
    Yes, all the same parameters - "Calculate Cut-and-Fill Volumes within Area Feature" and "Use Same Base Height Value for all Vertices" (0 metres). I'm measuring the same "Combine/Compare Terrain Layers" result in each case
  • Mark GaleMark Gale Global Mapper User Posts: 36Trusted User
    edited November 2014
    If I use the "Measure volume between Surfaces" function, the answer is somewhere between the other two answers!!
  • Andy WizmaAndy Wizma Global Mapper User Posts: 12Trusted User
    edited November 2014
    Definitely a bit strange, my only other suggestion is to try reducing the sample spacing and see what happens (don't think it should change the comparative results, but worth a try).

    Otherwise (maybe) there is something going on with your complex shape such that GM is calculating things differently between methods ... will have to leave that one to the GM experts. cheers
  • Andy WizmaAndy Wizma Global Mapper User Posts: 12Trusted User
    edited November 2014
    Just an update: with a more complex polygon shape I am getting differences between the two methods as well, around 0.3% (with a small sample spacing) ... so there is something going on ...
  • Mark GaleMark Gale Global Mapper User Posts: 36Trusted User
    edited November 2014
    I've tried copying a gmp file between different computers with v15 & v16 on them, it gives me an even greater choice of answers. :-)
  • Mark GaleMark Gale Global Mapper User Posts: 36Trusted User
    edited November 2014
    Any ideas from the GM team please on why the various methods I'm using to obtain volumes are giving me differing answers?? :(
  • Mark GaleMark Gale Global Mapper User Posts: 36Trusted User
    edited November 2014
    Anybody??? :(
  • Mark GaleMark Gale Global Mapper User Posts: 36Trusted User
    edited November 2014
    Please???? :(
  • DMcKittrickDMcKittrick Global Mapper Trainer Posts: 58Trusted User
    edited November 2014
    To clarify, when you first calculated the Cut and Fill values, you created the outline of the target area using the Measure tool. You then redrew the area with the Digitzer, which resulted in slightly different volume. Is it likely that when using the Digitizer, the position of certain vertices or shape points comprising the polygon may have been slightly different? This would cause the discrepancy in the volumetric calculations that you are seeing.

    - David McKittrick
    Senior Applications Specialist
    Blue Marble Geographics
  • Mark GaleMark Gale Global Mapper User Posts: 36Trusted User
    edited November 2014
    Hi David,

    Ithink I have two issues here:
    1. IfI take two surfaces, use "Combine/Compare Terrain Layers", then do a"Volume Calc", "Calculate Cut & Fill, "Use Same BaseHeight value for all Vertices" (0) using the Combined Elevation Grid, Iget a different value to a simple "Analysis", Measure Volume betweenSurfaces" using the original two surfaces (in the latest case, 265.59499cu m. to 257.65 cu m.)

    2. Difference in results between using the Measure Tool and Digitizer: granted, some of the vertices may be very slightly different, but having checked a number of times, the volumes still come out significantly more different than this could account for.

    Cheers.


  • MykleMykle Global Mapper User Posts: 435Trusted User
    edited November 2014
    The cube root of your results are 6.428 and 6.363m respectively, a difference of 65mm
    (assuming three equal and perpendicular sides).
    If you measure the side of a cube, you can probably get closer than that.
    Your volume appears to NOT be a regular shape, so I wonder how precisely you can define the volume.
    It doesn't take much of a bobble to significantly affect the results.
    I'm saying that without knowing how Global Mapper calculates volumes.
    This is an interesting discussion, since others have had issues in the past (with larger volumes).
  • DMcKittrickDMcKittrick Global Mapper Trainer Posts: 58Trusted User
    edited November 2014
    Mark Gale wrote: »
    Hi David,

    Ithink I have two issues here:
    1. IfI take two surfaces, use "Combine/Compare Terrain Layers", then do a"Volume Calc", "Calculate Cut & Fill, "Use Same BaseHeight value for all Vertices" (0) using the Combined Elevation Grid, Iget a different value to a simple "Analysis", Measure Volume betweenSurfaces" using the original two surfaces (in the latest case, 265.59499cu m. to 257.65 cu m.)

    2. Difference in results between using the Measure Tool and Digitizer: granted, some of the vertices may be very slightly different, but having checked a number of times, the volumes still come out significantly more different than this could account for.

    Cheers.



    To calculate the volume between two surfaces within the bounds of a specified area, use the Analysis > Measure Volume Between Surfaces function. This is a single calculation that will result in a more precise volumetric measurement. The alternative workflow that you followed is a two-stage calculation (Combine/Compare Terrain Layers function to create a third surface model followed by a calculation of the volume between this surface and base elevation of zero). Each of the two steps will inevitably result in a certain amount of rounding or interpolation which will cause the calculated values to be slightly different.

    - David McKittrick
    Senior Applications Specialist
    Blue Marble Geographics
  • Mark GaleMark Gale Global Mapper User Posts: 36Trusted User
    edited November 2014
    Thanks David, that certainly makes my ongoing volume calculations much more simple and less repetitive
  • güntergünter Posts: 11
    Hallo,
    ich habe einen Berg wo eine ebene Strasse durchlaufen soll.
    Wie kann ich das visualisieren
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