[Proj] *SOLVED*: Creating a nadgrid shift file with GDAL
j.l.h.hartmann at uva.nl
Mon Jan 21 09:12:00 EST 2013
This is the solution, thanks Andre.
On 01/20/2013 07:28 PM, Andre Joost wrote:
> dx values inverted:
To summarize: creating an ntv2 file with gdal utilities:
Let's say you have a list of coordinates in a non-wgs84 projection, and
a list of the same locations in wgs84. You want to create an ntv2-file
to shift from one to the other.
1) transfer the original coordinates to latlon, without a wgs84 shift
2) compute for each point the distance in degrees between the wgs84
location and the original latlon-location
3) separate the distance in its lon and lat component, and multiply both
numbers by 3600
4) invert the lon-value (<==== this was the problem)
5) create two point files, one for the lons and one for the lats. The
coordinates should be the wgs84 values, and the z-value the lon or lat.
Look on the gdal_grid page how to create a vrt-version, it's also
possible with postgis or any other ogr-format. Create also a point-file
with the same coordinates and all z-values set to zero
6) create for these three point-files each a gridded raster with
gdal_grid. Set reasonable boundaries in wgs84 with -txe and -ty, and
choose output format Float32
7) merge the grids into a four-band geotif: gdal_merge -separate -o
<shiftgrid> <latgrid> <longrid> <zerogrid> <zerogrid>. Mind the order:
8) invert the y-direction in <shiftgrid>: gdalwarp <shiftgrid>
<new_shiftgrid> (<=== this was another problem. Is this a bug?)
9) convert to ntv2: gdal_translate <new_shiftgrid> <ntv2_grid>
I would appreciate if someone would test the procedure on their own
data, and if it works, to add it to the documentation.
Thanks for all your help!
PS I fully agree with Gerald Evenden on the reversal of the lon-values
in the ntv2-format
I seem to get the idea that the Canadians developed this format---comments
please---and if they did then the designers deserve to be flogged for 8
with wet noodles for "positive east longitude." I can't believe it!!!!
is unbelievable arrogance by whoever had that stupid---yes, *VERY*
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Proj