[Proj] ostn02: northings and eastings to lats and longs
Roger Oberholtzer
roger at opq.se
Tue Nov 7 02:35:55 PST 2006
I am happily using proj to convert WGS84 lats and longs into OSTN02
eastings and northings. My C API code (seen in these parts before...)
is:
fromProj = pj_init_plus(
"+proj=latlong "
"+ellps=WGS84 "
"+towgs84=0,0,0 "
"+nodefs")
toProj = pj_init_plus(
"+proj=tmerc "
"+lat_0=49 "
"+lon_0=-2 "
"+k=0.9996012717 "
"+x_0=400000 "
"+y_0=-100000 "
"+ellps=airy "
"+towgs84=446.448,-125.157,542.060,0.1502,0.2470,0.8421,-20.4894 "
"+nadgrids=gb.gsb "
"+units=m "
"+no_defs")
Now, how would I specify these items if I wanted to go in the opposite
direction - from OSTN02 northings and eastings to WGS84 lats and longs?
Surely it is not just to turn around the fromProj and the toProj. Note
also that I am doing a grid shift via the "+nadgrids=gb.gsb " option.
I have a number of such conversions that I want to do, but one example
will get me on my way.
--
Roger Oberholtzer
OPQ Systems AB
Ramböll Sverige AB
Kapellgränd 7
P.O. Box 4205
SE-102 65 Stockholm, Sweden
Tel: Int +46 8-615 60 20
Fax: Int +46 8-31 42 23
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