Global Mapper v25.0

Problem converting 1 arc-sec float/grid to DEM

Bob Guba
Bob Guba Global Mapper UserTrusted User
edited March 2014 in Technical Support
When opening a NED 1 arc-sec float/grid elevation file (floatn42w070_1.flt) in Commonly Supported Elevation Types a menu comes up stating "The overlay type could not be determined from the file name you selected. Please select the type of overlay you wish to view." FLOAT/Grid (NED) is selected and this message comes up: "Unable to load header file C:|Users|Bob\App Data\Local\Microsoft\Windows\Temporary Internet Files\Content .IE5\SLC5D6N6\floatn42w070_1[1].ers". Last year I successfully converted 1/3 arc-sec float/grid files to DEMs using Global Mapper.

Comments

  • global_mapper
    global_mapper Administrator
    edited March 2014
    A .flt file by itself doesn't contain enough information to load the file, you also need a header file (usually .hdr or .ers) of some kind to provide the layout of the file (width and height in particular). Do you have any other files alongside the .flt file?

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Global Mapper
  • Bob Guba
    Bob Guba Global Mapper User Trusted User
    edited March 2014
    A .flt file by itself doesn't contain enough information to load the file, you also need a header file (usually .hdr or .ers) of some kind to provide the layout of the file (width and height in particular). Do you have any other files alongside the .flt file?

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Global Mapper

    There is an HDR file but it's not included when I open the FLT file.
    floatn42w070_1.flt
    n42w070_1as_meta.shp
    ned_larcsec_g.shp
    readme.pdf

  • global_mapper
    global_mapper Administrator
    edited March 2014
    Where is the .hdr file that you are referring to? You would need to download that along with your .flt as it likely describes the layout of the file so that applications know how to read it.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Global Mapper
  • Bob Guba
    Bob Guba Global Mapper User Trusted User
    edited March 2014
    Mike,
    The NED 1 arc-sec Float/Grid downloads as a zip file. When unzipped there is a folder, e.g.n42w071, that contains these files:


    floatn42w070_1.flt



    floatn42w070_1.hdr



    floatn42w070_1.prj



    n42w070_1_meta.xml



    n42w070_1as_meta.dbf



    n42w070_1as_meta.shp



    n42w070_1as_meta.shp.xml



    n42w070_1as_meta.shx



    ned_larcsec_g.dbf



    ned_larcsec_g.prj



    ned_larcsec_g.sbn



    ned_larcsec_g.sbx



    ned_larcsec_g.shp



    ned_larcsec_g.shx



    NED_DataDictionary.doc



    readme.pdf

    Click on Open Your Own Data Files, Common Supported Elevation Types, there is the FLT file but the HDR file is not included.




  • global_mapper
    global_mapper Administrator
    edited March 2014
    You don't need to load the .hdr file, it should be found next to the .flt file and used automatically. What are the contents of the .hdr file? If you load the .zip file directly in Global Mapper does that work?

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Global Mapper
  • Bob Guba
    Bob Guba Global Mapper User Trusted User
    edited March 2014
    Mike,
    I finally was able to create the 1 arc-sec (30 meter) DEM files inconveniently.
    The NED downloaded Grid/Float file is a ZIP file (Example: n42w072.zip). When I open GM and navigate to that file and have the file type Float/Grid (NED) selected it will not open even though it says it will open a *.zip file. In Windows Explorer the ZIP file has a sub- folder n42w072 with the extracted files. Selecting floatn42w072_1.flt leads to the messages I sent earlier. I found by a right click on the folder n42w072, selecting EXTRACT, a 2nd folder n42w072 with extracted files is created which I store in another folder. Opening GM and navigating to this 2nd n42w072 folder, selecting floatn42w072_1.flt, Float/Grid (NED) will bring up the graphic DEM where I can export it to a DEM file. Is this a Windows 7 problem or GM? My OS is Windows 7 Home Edition (64 bit) and GM is Ver 15.1.7 (32 bit).
  • global_mapper
    global_mapper Administrator
    edited March 2014
    That is odd, directly loading the .zip file with File->Open Data File should work. You don't want to explore into the zip and try to open the .flt there and Windows will just make the file that you selected available through it's seamless unzipping, so Global Mapper can't see the .hdr. Of course manually extracting then loading the .flt will make the .hdr available, but just loading the .zip directly in Global Mapper should do the same thing behind the scenes.

    Can you provide the file to me (or point me to where I can download it)?

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • Bob Guba
    Bob Guba Global Mapper User Trusted User
    edited March 2014
    Mike,
    I have determined my problem was with Windows 7. This morning when I turned on my computer it downloaded and installed a large Windows update. After rebooting I read your last reply and decided to try again opening GM with the downloaded ZIP file from the USGS National Map Viewer ( USGS TNM 2.0 Viewer ) before sending you the ZIP file. This time when selecting the file it placed it in the File window which it hadn't done before. With file type as Float/Grid, Open brought up the screen asking for projection info after which a tiled map of the USA and territories appeared - the tile selected being blacked out. Setting Export to Elevation Grid, DEM, created the DEM file. All I can say is after the Windows update the problem was fixed (another Windows mystery). Here is the link to my Dropbox for downloading a 1 Arc-Sec Grid/Float ZIP file. https://www.dropbox.com/s/npipp1jk2extrz5/n42w072.zip

    Thank you for your attention to my help request,
    Bob Guba