Global Mapper v25.0

Slope X,Y Values

digitalaviator
digitalaviator Global Mapper UserTrusted User
edited June 2014 in Vector Data
Hi Mike,

I have a question I've been meaning to ask for years. Is there a way to utilize elevation data to figure out the slope of a water polygon as an X,Y value? In my case I could just add the elevation data to each vector point on a lake or river and try and flatten the terrain that way, but then I'd have undulating water bodies. What I need to be able to do is to burn a steady flat slope into my elevation data without it stair stepping or being a bunch of irregular triangular sections.

i.e. it needs to basically average out the slope over the polygonal vector data then I need to be able to generate my sloped water flattens from there and blend the flattened water body elevation data into the underlying elevation data.

Cheers,
Dean.

Comments

  • Josie_BMG
    Josie_BMG Global Mapper User
    edited June 2014
    Hi Dan, Can you please provide a bit more information about your question. Do you have elevation data for your water polygon that you want to create a surface from? Or do you have a DEM that you want to create a polygon with elevation data from?
  • global_mapper
    global_mapper Administrator
    edited June 2014
    Dean,

    I would suggest creating your flattened grid from the water polygon, then go to the Feathering tab of the OPtions dialog for the flattened grid and feather the edges into the underlying terrain so you get a smooth transition. It should take a very large feather, maybe 10-15 samples, to eliminate any noticeable transition.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • digitalaviator
    digitalaviator Global Mapper User Trusted User
    edited June 2014
    Hi Mike,

    Microsoft ESP and Lockheed Martin Prepar3d all use vector polygons to flatten the water. In my example I have 5m autocorrelated elevation data for all of Utah and need to flatten the rivers. However in order to make it work correctly in the sim platform, I need to match both a vector polygon for the water and also burn that vector polygon into an elevation flatten in the same method you mentioned above.

    From the SDK Terrain and Scenery


    WaterPolys
    SlopeX
    11
    Slope in vertical meters per degree of longitude. 13 char floating point number.
    Slope
    {CEB07D86-3605-44BE-B48A-97F8D01B74DE}


    WaterPolys
    SlopeY
    11
    Slope in vertical meters per degree of latitude. 13 char floating point number.
    Slope
    {CEB07D86-3605-44BE-B48A-97F8D01B74DE}


    The SlopeX and SlopeY values are what I need to be able to add into my water polygons. I might be overthinking it though if I do indeed just burn the data into the elevation data, but in my experience before that led to a stair stepping effect instead of a smooth slope on the surface of the water.
  • global_mapper
    global_mapper Administrator
    edited June 2014
    Dean,

    Ah I see, I thought they were flat water polygons, like a lake, rather than a river with different elevations at different locations. Since a polygon isn't a linear feature it is a bit odd to have a slope from one "end" to another, but in this case the polygons are likely special and can be approximated with a linear feature.

    If you have a linear feature for the river polygons where you know the start and end elevation of the section, you could perhaps buffer those and then create a terrain surface from the buffer, then assign elevations to the actual water polygons from the terrain surface created from the smoothly transitioned buffer areas from the 3D linear features. Then you could grid the now 3D water polygons and feather them a little in to the terrain. I can imagine this might have some issues though.

    Can you maybe provide a sample of what the data looks like and what you are trying to get it to?

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation