Global Mapper v25.0

DEM Altering 101

rbp71854
rbp71854 Global Mapper User
edited March 2010 in Elevation Data
I am using Global Mapper to process gtopo30 DEMs and 2000 Tiger shape files as input files to create mesh terrain and ocean area features in MS Combat Flight Simulator 3. As shown in the attached screenshot I have one particular area where the underlaying DEM terrain area is bleeding through the uper water shape file area. All other areas of the Hawaiin Island chain are okay.

In the contours screenshot of Moloka island the contour lines at some locations extend into the ocean area.

Being a noob in the manipulation of DEM data I am at a loss on how to adjust the elevations lower in those instances of above 0 meters at those locations in the ocean area feature.

Your patience and help with this neophyte is appreciated.

Bob

Comments

  • global_mapper
    global_mapper Administrator
    edited March 2010
    Bob,

    The easiest way to adjust the elevations for a particular area of terrain is to create an area feature with the Digitizer Tool and assign it an ELEVATION attribute with the adjustment amount (like say '-5 m' to lower by 5 meters). Then, select the area, right-click, select the Advanced Feature Creation menu option to Create/Flatten terrain, then check the box that elevations are relative to the terrain. This should create a new terrain patch in the area with the underlying terrain adjusted down by 5 meters.

    In this case though I might recommend using a better source for the original terrain than GTOPO30, like perhaps the NED data source built into Global Mapper on the File->Download Online Imagery/Data menu command. That source will have much more detail and accuracy than GTOPO30.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • Frank2
    Frank2 Super Moderator
    edited March 2010
    And in fact, 10m DEM data is available:
    http://gis.ess.washington.edu/data/raster/tenmeter/hawaii/
  • rbp71854
    rbp71854 Global Mapper User
    edited March 2010
    Thanks Folks for the quick reply. I really do appreciate the help. I will take your advice on using another DEM 1st and see if that resolves my problem.

    I was missing the bit about adjusting by -5 meters before flatening the terrain when I attempted to do that.

    Thanks again for the help

    Bob