Global Mapper v24.1

Creating slope polygons

DustyRobinson
DustyRobinson Global Mapper UserTrusted User
edited October 2013 in Elevation Data
I am trying to create slope polygons from a surface. I want my final polygons to be grouped into slopes of:
0-15
15-25
25-40
40-60
>60

What is the best way to obtain the slope polygons?

Comments

  • 946
    946 Global Mapper User Trusted User
    edited October 2013
    Hi,

    You coud export the surface to Float/Grid file and check the option to Export slope values insted of Elevation.
    Import in GM the .flt and use create areas features from equal values(with a value of 5). Than you can split the layer based on ELEVATION(that is the slope infact) and group as you want.

    All teh best
  • DustyRobinson
    DustyRobinson Global Mapper User Trusted User
    edited October 2013
    Thanks. That gets me close, but I can't get figure out how to get the exact breakout like I listed. I am also confused about something the flt file is showing me. When I open it, the values it is showing do not correspond to the slope values that it should have, nor is it the elevations. When I created area features from equal values the values where in the right range. I need a way to set exact classifications of the areas to get the values I need.
  • global_mapper
    global_mapper Administrator
    edited October 2013
    An easier approach to get exactly those ranges since they aren't on the same multiples is to create a custom shader on the shader drop-down and specify the ranges you want and check the box to indicate it is a slope shader. Then specify a different color for each range. Once you have the display you want, export to an image file, like a 24-bit GeoTIFF, with File->Export->Export Raster Data. Load that back in, then right-click on the layer in the Control Center and select to create areas from equal value areas. You should get areas for each separate range.

    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
  • fullsam50
    fullsam50
    Hey Mike,
    I'm using version 19.0.2.
    I have the same query as Dusty above. 
    I tried the method you described.
    However, with a 24-bit GeoTIFFs, the output is very rough/pixilated irrespective of the resolution I prescribe.
    Using other methods, I get similarly mixed results.
    With a PDF, the colors are not crisp on re-import so the "create areas from equal value area" functions produces far more polygons than the initial.
    With other raster outputs, the elevation grid is embedded, so the files are enormous (I have a vast amount of data to process).

    My question is whether a better function (which i cannot find) has been developed in the GM versions since your reply in 2013.

Categories

In this Discussion