Global Mapper v25.0

GlobalMapper fills DTED file voids with data?

yigal
yigal Global Mapper User
edited November 2008 in Elevation Data
Hi,
I have a DTED level 1 file with some voids. When I review it with GlobalMapper (anti-aliasing is off) I can't see any empty spots, all the data looks OK. However when I review the DTED file using binary viewer I observe the voids. More than that when I export the data to GeoTIFF elevation file and open it with image viewer I'm able to see voids, but if I load the exported GeoTIFF to GlobalMapper the voids disapeared. So the question is the GlobalMapper fills the small voids automatically?:confused:

Comments

  • global_mapper
    global_mapper Administrator
    edited November 2008
    That is strange, Global Mapper should not be automatically filling any voids during display. Can you send me (or post) the file so that I can take a look?

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • yigal
    yigal Global Mapper User
    edited November 2008
    I'm sorry, my mistake. I forgot that DTED negative values are sign magnitude and in that particular file were "sea-level" zeroes 0x8000 which I, erroneously, consider as voids. However, the DTED-to-GeoTIFF export "supported" my mistake.As you can see, the white dots in attached file (JPEG converted from GeoTIFF) are at the places of those "negative zeroes" tracking coast line.
  • global_mapper
    global_mapper Administrator
    edited November 2008
    Can you send me the file in question so that I can take a look? I would expect a value of 0x8000 in the DTED file to just be zero and get output to the GeoTIFF file as such.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • yigal
    yigal Global Mapper User
    edited November 2008
    Sent to e-mail
  • global_mapper
    global_mapper Administrator
    edited November 2008
    I took a look and discovered that there are actually a bunch of true negative values near the shoreline (usually in the -1 to -4 meters range). When you export these to a 16-bit vertical GeoTIFF they are going to be written as normal 2s complement numbers, when would look like very large numbers if you treated the values as unsigned 16 bit values, like a application that interpreted the 16-bit GeoTIFF as an image rather than a series of gridded signed values would.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com