On 11-04-12 06:07 PM, Brian Wilson wrote:
Trying to get a raster to go from NAD83 to NAD27 with gdalwarp. Can't see any
way to tell how it is choosing to do it. Is this documented anywhere? Is there
any way to make it verbose so I can tell if it's trying?
I ran it through strace and watched it open a file called gdal_datum.csv but of
course can't tell what it's trying to do.
I found this post from Frank which implies it tries to be smart and figure out
the transforms without my help:
http://fwarmerdam.blogspot.com/2010/03/in-last-few-weeks-i-believe-i-have-made.html
But it's not working and since I don't know how to tell what it's doing I can't
intelligently ask for help. :-)
Thanks for your patience with a n00by
Brian
Command I am using:
gdalwarp -of HFA -co COMPRESSED=YES -t_srs
ESRI::NAD_1927_StatePlane_Oregon_North_FIPS_3601.prj 11s5w34f_color_ne.sid
11s5w34f_color_ne_nad27.img
Output is in the right coordinate space (it's moved from meters to feet) but
has that familiar 10 or so meter shift we get around like the NAD83-NAD27
transform failed.
The input file SRS looks like this
Coordinate System is:
PROJCS["NAD_1983_HARN_StatePlane_Oregon_North_FIPS_3601",
GEOGCS["GCS_North_American_1983_HARN",
DATUM["NAD83_High_Accuracy_Regional_Network",
SPHEROID["GRS_1980",6378137,298.257222101]],
PRIMEM["Greenwich",0],
UNIT["Degree",0.017453292519943295]],
PROJECTION["Lambert_Conformal_Conic_2SP"],
PARAMETER["False_Easting",2500000],
PARAMETER["False_Northing",0],
PARAMETER["Central_Meridian",-120.5],
PARAMETER["Standard_Parallel_1",44.33333333333334],
PARAMETER["Standard_Parallel_2",46],
PARAMETER["Latitude_Of_Origin",43.66666666666666],
UNIT["Meter",1],
AUTHORITY["EPSG","102326"]]
Brian,
I believe the problem is the source datum name
"NAD83_High_Accuracy_Regional_Network". I believe
this is *not* recognised as essentially NAD83 and so
the source datum is treated as unknown and no datum
shifts are done.
It can be helpful to run gdalwarp with the commandline
option "--debug on" in which case the debug output should
include the PROJ.4 rendering of the source and destination
coordinate system.
At a very low level you can also define the PROJ_DEBUG environment
variable to the value ON and PROJ.4 will report some details on what
datum files are opened.
I think you are going to have to provide a source coordinate
system with the -s_srs commandline switch to gdalwarp that
defines a more conventional NAD83 based coordinate system. You
might also want to file a ticket on this issue. Ideally we
would be smarter about treating NAD83 HARN as equivelent to NAD83
for most purposes.
Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up | Frank Warmerdam, [email protected]
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush | Geospatial Programmer for Rent
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