Global Mapper v25.0

S57 -> DEM accuracy issues

wakestrap
wakestrap Global Mapper User
edited April 2012 in Elevation Data
Guys,
I'm using spot sounding data from a number of S57 charts to create a DEM or GeoTiff of the bathymetry. I'm having an issue with accuracy in the output. The S57s being used cover varying levels of accuracy and when I take away all other layers but spot sounding, convert to elevation grid then export as a geotiff I'm finding that I'm losing the accuracy from the lowest scale factor charts.
What's strange is even when I JUST export using only a single chart at the lowest scale factor, my final output is still off by 2-5 meters in places. I'm guessing it's a settings issue but anyone have any tips?
Cheers,
A

Comments

  • global_mapper
    global_mapper Administrator
    edited April 2012
    What grid resolution is being used when you calculate the grids? For widely spaced spot soundings the default grid spacing that is used could have grid cells that are quite large, with the actual sample location at the center of the grid cell and far from the actual spot sounding. If you manually force the grid spacing tighter it will be truer to the actual spot sounding locations, but at the price of much larger grid files.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    gmsupport@bluemarblegeo.com
    http://www.globalmapper.com
  • wakestrap
    wakestrap Global Mapper User
    edited April 2012
    Thanks Mike, that seems to do the trick. I guess you were already communicating with my colleague about a related issue today, thanks for a the fantastic support.
    Cheers,
    A