Global Mapper v25.0

How to export .bil elevation data to xyz with the exact decimal precision?

Sandhya18
Sandhya18 Global Mapper User
edited October 2013 in Elevation Data
I am using Global Mapper v13. I have input DSM data in. bil with 6 decimal precision. I converted the .bil to .xyz in Global Mapper for further editing (to remove anomaly in DSM). After processing, the output will be in ASCII format. Then I converted the output to .bil to deliver the results. When I compared the results manually, they were exactly matched. But When Using Combine Terrain Layers, there were errors between -0.000001 and 0.000001 in all the points.

When checking the error step by step, the error occurred in the initial process that the conversion process from .bil to .xyz doing decimal rounded off to three decimals. Even I cannot view the original decimals in Global Mapper.


And also I searched in the GlobalMapperHelp.pdf about decimal precision. There I found;

"ADVANCED USERS - In Global Mapper v11.02 and later you can customize the number of decimal digits written out for the X and Y coordinates for a CSV export through the use of a DWORD registry key 'HKEY_CURRENT_USER\Software\Global Mapper\ASCIIExportCoordPrecision'. For example, set this value to 6 to get 6 decimal digits for each X, Y, and Z coordinate."

I followed the steps but not got the precised output.

Is there any other way to export the full floating point BIL to XYZ with the same precision in Global Mapper 13 or which format best suits to get the same decimal precision? Though the difference is too small, there is no option to deliver the file with loosing the precision. Kindly help me to achieve the precision as in the original.

Thanks in advance

Sandhya

Comments

  • global_mapper
    global_mapper Administrator
    edited September 2013
    Sandhya,

    There isn't any way in v13 to do that, you would need the new v14 build with the registry support for precision on XYZ grid export. Note that your BIL is a 32-bit floating point BIL which supports about 10 digits after the decimal for values of your size, but almost certainly the elevations are really only accurate to maybe 2 or 3 digits, the rest is just slight offsets since floating point can't exactly store many decimals. So when you write out to a text format that can exactly specify things with 2 or 3 digits of precision you get very tiny differences simply due to a binary vs. decimal representation. Even extended the number of decimal digits only makes the problem smaller. You won't get an exact match on some numbers when comparing a floating point binary vs. a decimal representation, but the differences are many orders of magnitude too small to matter unless measure the position of individual atoms!

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • Sandhya18
    Sandhya18 Global Mapper User
    edited October 2013
    Mike,

    I have installed Global Mapper v15 and downloaded the support file for registry key but it is not working. What causes the problem?

    Thanks
  • Sandhya18
    Sandhya18 Global Mapper User
    edited October 2013
    Sir,
    I have purchased and installed Global Mapper v15 64-bit and I want the registry support file for v15 to export XYZ grid with precision. And also I need to export the edited ASCII again to .bil with the same precision. Kindly do the needful sir. Thank you.







  • global_mapper
    global_mapper Administrator
    edited October 2013
    If you have the latest v15 build the XYZ grid export should contain a section on the export dialog where you can specify how many digits of precision to store in the file for Z value. I have placed a new build at http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15.zip with the latest changes for you to try. Simply download that file and extract the contents into your existing v15.xx installation folder to give it a try. If you are using the 64-bit v15 version there is a new build at http://www.bluemarblegeo.com/downloads/global-mapper/global_mapper15_64bit.zip .

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation