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<div class="Normal"><span style='font-size: 10pt; '>Dear List</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>we have some problems using
grid shift files. We are using a grid shift file which was developed by the
Swiss Federal Office of Topography [1]. We just duplicated epsg 21781 (to
921781) and 2056 (to 902056) in the epsg file and added
"+nadgrids=chenyx06.gsb" and "+nadgrids=@null":</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>21781:
</span><br><span style='font-size: 10pt; '>+proj=somerc +lat_0=46d57'08.66"N
+lon_0=7d26'22.50"E +ellps=bessel +x_0=600000 +y_0=200000
+towgs84=674.374,15.056,405.346 +units=m +k_0=1 +no_defs </span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>2056:</span><br><span style='font-size: 10pt; '>+proj=somerc
+lat_0=46d57'08.66"N +lon_0=7d26'22.50"E +ellps=bessel +x_0=2600000 +y_0=1200000
+towgs84=674.374,15.056,405.346 +units=m +k_0=1 +no_defs</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>921781:
</span><br><span style='font-size: 10pt; '>+proj=somerc +lat_0=46d57'08.66"N
+lon_0=7d26'22.50"E +ellps=bessel +x_0=600000 +y_0=200000
+towgs84=674.374,15.056,405.346 +units=m +nadgrids=chenyx06.gsb +k_0=1 +no_defs
</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>902056:</span><br><span style='font-size: 10pt; '>+proj=somerc
+lat_0=46d57'08.66"N +lon_0=7d26'22.50"E +ellps=bessel +x_0=2600000 +y_0=1200000
+towgs84=674.374,15.056,405.346 +units=m +nadgrids=@null +k_0=1
+no_defs</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>4326:</span><br><span style='font-size: 10pt; '>+proj=longlat
+ellps=WGS84 +datum=WGS84 +no_defs</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>904326:</span><br><span style='font-size: 10pt; '>+proj=longlat
+ellps=WGS84 +datum=WGS84 +nadgrids=@null</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Here are the
results:</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>21781 -> 2056:
correct!</span><br><span style='font-size: 10pt; '>921781 -> 90256: correct
(with grid shift file)!</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>but:</span><br><span style='font-size: 10pt; '>921781
-> 2056: wrong!</span><br><span style='font-size: 10pt; '>921781 -> 4326:
wrong!</span><br><span style='font-size: 10pt; '>921781 -> 904326:
wrong!</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Is the grid shift only
applied if the destination definiton has a "+nadgrids=@null"? But then why is
the transformation to 904326 not correct? Has this something to do with this bug
report [2]? Or I'm just mixing up some parameters? Same results with Proj 4.5
and 4.6.1. Any help is appreciated.</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>regards</span><br><span style='font-size: 10pt; '>Stefan</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>[1]:
http://www.swisstopo.admin.ch/internet/swisstopo/en/home/topics/survey/lv03-lv95/chenyx06/distortion_grids.html</span><br><span style='font-size: 10pt; '>[2]:
http://trac.osgeo.org/proj/ticket/22</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Mit freundlichem
Gruss</span><br><span style='font-size: 10pt; '>Stefan
Ziegler</span><br><span style='font-size: 10pt; '>Leiter Aufsicht</span></div>
<br>
<div class="Normal"><span style='font-size: 10pt; '>Kanton
Solothurn</span><br><span style='font-size: 10pt; '>Bau- und
Justizdepartement</span><br><span style='font-size: 10pt; '>Amt für
Geoinformation</span><br><span style='font-size: 10pt; '>Rötistrasse
4</span><br><span style='font-size: 10pt; '>4501
Solothurn</span><br><span style='font-size: 10pt; '>Telefon 032 627 75
96</span><br><span style='font-size: 10pt; '>Telefax 032 627 75
98</span><br><span style='font-size: 10pt; '>stefan.ziegler@bd.so.ch</span><br><span style='font-size: 10pt; '>http://www.so.ch</span></div>
<br>
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