find volume of a lake?

JSLJSL Global Mapper UserPosts: 422Trusted User
edited January 2014 in Technical Support
Hi, I've created a polygon from contour lines over a depression, and I'm trying to find what the volume would be of a virtual lake whose surface is the polygon. When I select the polygon and use the calculate volume command, which option should I click, "Use same base height," or "Use heights from terrain surface"? If it's "Use Same Base Height Value," should I use the elevation of the contour line? Also, I 'm unclear about what's the difference is between the cut and fill numbers that are generated.

Thanks for any help...

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited January 2014
    In the case of a contour where the edge of the polygon is all one height you can just select 'Use Same Base Height' and enter the contour height. Although the 'Use Heights from Terrain Surface' should also get the same results if the contours were from the terrain.

    In the case of a depression the Fill Volume would be the volume of the depression (fill volume is volume between cut surface and terrain surface.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • JSLJSL Global Mapper User Posts: 422Trusted User
    edited January 2014
    Thanks very much. I have another question--is there an easy way to find the average elevation and slope of a line? Right now, I'm creating a series of points from line segments, applying terrain values, and then exporting to csv and performing calculations in the spreadsheet. It works, but it's time-consuming.

    Thanks for your help...
  • CassandraQCassandraQ Global Mapper User Posts: 34Trusted User
    edited January 2014
    To get the average elevation, set up the data so each point is a feature. Open the Search Dialog, each point should be listed. Select all the features and right click over the elevation values and select STAT. This should return the average elevation for all features selected. The average slop of a line can be found by selecting the line with the digitizer tool, right-clicking and going to Analysis/ Measurement. The option Calculator elevation/ slope stats should return the average slop value.

    Please let me know if this is not returning the results you are looking for.

    Cassandra
  • JSLJSL Global Mapper User Posts: 422Trusted User
    edited January 2014
    Thank you for that information. Maybe for the future, you might consider configuring the "Analysis/Measurement-Calculate elevation slope stats" command so that it returns the average elevation as well as the average slope, because the method that you described works well for one line, but is very cumbersome for many lines.

    Thanks again...
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited January 2014
    Actually the option to calculate elevation/slope statistics for selected area/line features from the Digitizer Tool should calculate the AVG_SLOPE for each line and add it to the attributes, so you can simply select all lines of interest, then use that option to calculate the elevation/slope statistics for them all. Then each line will have attributes added to them with the elevation/slope stats.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • JSLJSL Global Mapper User Posts: 422Trusted User
    edited January 2014
    Hi Mike, sorry I wasn't more clear--what I meant to say was that, while it is very helpful to be able to currently calculate average slope of a line, it would also be very helpful to have the command calculate the average elevation of a line as well.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited January 2014
    Ah I gotcha. I have updated the elevation/slope stats for lines to also include an AVG_ELEV attribute for the line. I have placed a new build at http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15.zip with the latest changes for you to try. Simply download that file and extract the contents into your existing v15.xx installation folder to give it a try. If you are using the 64-bit v15 version there is a new build at http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15_64bit.zip .

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • JSLJSL Global Mapper User Posts: 422Trusted User
    edited January 2014
    Awesome, thanks!
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