[Proj] Call for review of derived NTv2 for Swiss projection CH1903

Sandro Santilli strk at keybit.net
Wed Feb 1 17:21:15 EST 2012

I've finally handled to derive an gridshift for CH1903->WGS84
so that it can be used w/out engaging chains of projections.

The procedure I followed to generate the new file has been:

 1) Project each of the NTv2 grid points to WGS84 using the
    chained approach (CH1903 -> CH1903+ -> WGS84)
 2) Compute the shifts between output and source
 3) Store the shifts in the new NTv2

More details on the how I'll probably give later with a blog post
as it was a complex and interesting trip around GDAL and PostGIS.

The verification I performed has been to project from CH1903/LV03,
using these parameters:

<CH1903_LV03> +proj=somerc +lat_0=46.95240555555556 +lon_0=7.439583333333333 +k_0=1 +x_0=600000 +y_0=200000 +ellps=bessel +nadgrids=CHENYX06a_wgs84.gsb +units=m +no_defs  <>

To CH1903+/LV95 (using EPSG:2056) and computing the distance of each
of the 5 example points found in Chapter 7 of

I got a max of 9mm drift.

This mail is to ask others to try the NTv2 file with real data and
let me know if it's working as expected.

The new NTv2 file is here:
http://strk.keybit.net/tmp/CHENYX06a_wgs84.gsb.gz (~ 1Mb)

Thanks in advance.


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