[GRASS-user] Importing DEM data with different projections

Rich Shepard rshepard at appl-ecosys.com
Tue Sep 17 14:41:21 PDT 2019

The Oregon LiDAR data were acquired over several years under different
contracts with the same provider company. These are available by 7.5"
topographic quad names using the Ohio system. In the directory, LDQ-45123G1/
there are four input files.

Using the GUI location manager I created a new location (G1) and imported
the map 2009_OLC_Hood_to_Coast/.../hdr.adf. When I tried to import
2009_OLC_North_Coast/.../hdr.adf r.in.gdal complained that the projection of
the location did not match that of the new data to be imported:

WARNING: Datum <Not_specified_based_on_GRS_1980_ellipsoid> not recognised by GRASS and no parameters found
WARNING: Projection of dataset does not appear to match current location.

Location PROJ_INFO is:
name: unnamed
ellps: grs80
proj: lcc
lat_1: 44.33333333333334
lat_2: 46
lat_0: 43.66666666666666
lon_0: -120.5
x_0: 2500000
y_0: 0
no_defs: defined

Dataset PROJ_INFO is:
name: unnamed
ellps: grs80
proj: lcc
lat_1: 43
lat_2: 45.5
lat_0: 41.75
lon_0: -120.5
x_0: 399999.9999999999
y_0: 0
no_defs: defined

ERROR: x_0

Why the source agency has different projections for flights over the same
topographic quad area is not anything I want to pursue. My question to you
gurus is how do I handle these situations? Do I just override the dataset's
projection and force it to use the existing location's?

I had one quad with 5 maps, two had the projection of the first one above,
three had the projection shown second above. I created a separate location
for each map then reprojected each to my statewide location. I'm sure
there's a more efficient way to handle these discrepancies.



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