Global Mapper Pro

Exporting online elevation data

Mykle
Mykle Global Mapper UserTrusted User
edited October 2014 in Bug Report
Note: the issue described here has been bypassed by using a more time-consuming method as noted at the end. While it is not an immediate problem, it would be nice for GM to handle the issue.

Global Mapper v16.0.0 (b091714) [64-bit] - REGISTERED
(same behavior in v15.2)

Create a range ring at 32 25 N 112 50 W, radius 167 km
(geophysical gravity measurements require a lot of processing steps, one of which is a correction for terrain using elevation data out to 167 km)

Zoom to include all of the range ring, then download from the Online Data Source for "United States Elevation Data (NED) (30m Resolution)", using default parameters (like Current Screen Bounds). This is the import statement from the GMW file (with some added CR/LF by me):
IMPORT_WMS SOURCE_DESC="United States Elevation Data (NED) (30m Resolution)"
WMS_SERVER_URL="http://wms.jpl.nasa.gov/wms.cgi" \
WMS_SERVICE="WMS" WMS_LAYER="us_ned"
WMS_STYLE="feet_short_int"
LAYER_DESC="United States Elevation Data (NED) (30m Resolution)" \
LABEL_FIELD_FORCE_OVERWRITE="NO"
SAMPLING_METHOD="BILINEAR"
CLIP_COLLAR="NONE"
ELEV_UNITS="METERS"

Note that the data extend into Sonora, Mexico at the bottom left, and then out into the Gulf of California.

Export the elevation data to a Global Mapper Grid file.

All of my attempts have hung when over half way done (left for over 12 hours). Shift the export area to the east so that all of the display contains defined values, and it exports fine in a few minutes. Ditto to the north.

Download SRTM covering the same area, and it exports fine.

Load the 30m data on top of the SRTM and it fails.

Close all of the Online Data source layers.

Manually download 1-arc-second NED data files from viewer.nationalmap.gov to cover the area. With SRTM underlaying so the blank areas to the southwest are defined, export the elevation data file. No problem.

Does GM have any methods to recognize and skip areas where elevation data are not available from an online source like USGS?

Thanks,
Mykle

Comments

  • DMcKittrick
    DMcKittrick Global Mapper Trainer Trusted User
    edited September 2014
    Mykle,

    I just ran some tests and I did find some issues with the speed of export when accessing the 30m NED. The fact that part of your export bounds polygon contained no data should not be an issue but I have submitted a bug report so we can take a closer look at the issue.

    In the meantime, there are a couple of alternative workflows that you can try. Instead of cropping during export, try cropping the NED data in the Elevation Options dialog box. Open the Overlay Control Center (Alt+C), click the Options button, and select the Cropping tab to find this tool. After the data has been cropped, try exporting without imposing any further cropping in the Export Options dialog box.

    I found that the 10m NED WMS service was somewhat faster. Try exporting from that source and if necessary, change the Sample Spacing to 30m x 30m.

    I hope this helps.

    - David McKittrick
    Senior Applications Specialist
    Blue Marble Geographics
  • Mykle
    Mykle Global Mapper User Trusted User
    edited October 2014
    David,

    Thanks for the notes and workaround. Again, I completed this task by downloading separate elevation data files from USGS. Exporting data from an online data source was counter-productive, but informative as a poor example.

    Speed is a concern only if it is zero. A procedure that does not complete is a problem (an informative abort is much more useful). That said, it is good that you found other speed issues worth addressing.

    Mexican elevation data are available for 30m and not 10m. A significant portion of my area was in Mexico, hence my choice of 30m. There is 1/9 arcsecond data available along the border (one project that I had within this band was very nice to work with). I am developing a habit of checking for Lidar coverage for each of my projects! It is very nice to look at next-generation US Topo maps that use Lidar elevation data for contours, where a state has complete coverage. But I digress ...

    The only cropping that I did was in the Export Options dialog, Export Bounds, "All Data Visible On Screen" (I did not crop to the range ring, but zoomed to the layer containing the range ring to ensure that sufficient coverage was included). I normally use the layer options to trim maps, so will have to play with using it to crop elevation data. That method looks interesting!

    Thanks,
    Mykle
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