Global Mapper Pro

Wrong datum for NBDS CRS with LAS files

Hi -

I noticed a possible problem with Global Mapper with regard to its auto-identification of coordinate reference systems for LAS files. Specifically, it's getting the datum wrong, using NAD83 instead of NAD83(CSRS) when New Brunswick Double Setereographic (aka NBDS) is used.

The project where the issue arises uses the NBDS projection, with the NAD83(CSRS) datum; the EPSG code for the project is 2953. The headers in the LAS files, as shown by lasinfo, all agree that the files are in NAD83(CSRS).

However, when LAS files from the project are brought in to Global Mapper, Global Mapper auto-identifies them as being in the NAD83 (original) datum, with EPSG code 2036.

The problem has only occurred with LAS files. SHP files in EPSG 2953 work as expected.

The problem occurs in GM17 and GM18.

LAS files generated on two different machines show the same problem. The LAS data itself is very likely correctly positioned; it has been successfully tested against ground control.

I have the output from lasinfo as well as the metadata from GM17 saved; I can post the full text if necessary. Thanks in advance for any help.

This is the relevant part of the metadata, from GM17, for a file that showed the problem:

~~~

PROJ_DESC=New Brunswick Double Stereographic / NAD83 / meters
PROJ_DATUM=NAD83
PROJ_UNITS=meters
EPSG_CODE=EPSG:2036

~~~

This is the relevant part of the lasinfo output for the same file:

~~~

variable length header record 3 of 4:
  reserved             43707
  user ID              'LASF_Projection'
  record ID            34737
  length after header  156
  description          'GeoASCIIParamsTag (optional)'
    GeoAsciiParamsTag (number of characters 156)
      NAD83(CSRS) / NB Stereographic NAD83 / CGG2013N|NAD83(CSRS)|NAD83(CSRS) / NB Stereographic NAD83 / CGG2013N|NAD83(CSRS) / NB Stereographic NAD83 / CGG2013N|
variable length header record 4 of 4:
  reserved             43707
  user ID              'LASF_Projection'
  record ID            2112
  length after header  790
  description          'OGC COORDINATE SYSTEM WKT'
    WKT OGC COORDINATE SYSTEM:
    PROJCS["NAD83(CSRS) / NB Stereographic NAD83 / CGG2013N",GEOGCS["NAD83(CSRS) / NB Stereographic NAD83 / CGG2013N",DATUM["NAD83(CSRS)",SPHEROID["GRS 1980",6378137.000,298.257222101,AUTHORITY["EPSG","7019"]],AUTHORITY["EPSG","6140"]],PRIMEM["Greenwich",0.0000000000000000,AUTHORITY["EPSG","8901"]],UNIT["Meter",1.00000000000000000000,AUTHORITY["EPSG","9001"]],AUTHORITY["EPSG","0"]],PROJECTION["Oblique_Stereographic"],PARAMETER["latitude_of_origin",46.5000000000000071],PARAMETER["central_meridian",-66.5000000000000000],PARAMETER["scale_factor",0.9999120000000000],PARAMETER["false_easting",2500000.000],PARAMETER["false_northing",7500000.000],UNIT["Meter",1.00000000000000000000,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH],AXIS["Height",UP],AUTHORITY["EPSG","0"]]

~~~
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