[Proj] converting WGS84 to NAD27

Anna Hentzel wibge at gmail.com
Sun Oct 4 17:22:03 EST 2009


I'm trying to convert WGS84 coordinates to UTM and NAD27. I'm using
the route-me library, which is a thin wrapper on proj4. It just
creates the PJ objects using pj_init_plus on the strings, and calls
pg_transform. The transformation to UTM works correctly, but the NAD27
transformation doesn't change the coordinates. Does anyone know what I
might be doing wrong?

CLLocationCoordinate2D coord = {60, -119};
int zone = ((coord.longitude + 186) / 6);

RMProjection* latLonProj = [[RMProjection alloc]
initWithString:@"+proj=latlong +ellps=WGS84 +datum=WGS84"];
RMProjection* utmProj = [[RMProjection alloc] initWithString:
[NSString stringWithFormat:@"+proj=utm +zone=%d +ellps=WGS84", zone]];

RMTransform* trans = [[RMTransform alloc] initFrom:latLonProj To:utmProj];

CLLocationCoordinate2D transCoord = [trans projectForward:coord AtZoom:9];
NSLog(@"UTM Coord %f, %f %d" , transCoord.latitude, transCoord.longitude, zone);

RMProjection* nad27Proj = [[RMProjection alloc]
initWithString:@"+proj=latlong +ellps=WGS84 +datum=NAD27 +no_defs"];
trans = [[RMTransform alloc] initFrom:latLonProj To:nad27Proj];
transCoord = [trans projectForward:coord AtZoom:9];
NSLog(@"NAD27 Coord %f, %f" , transCoord.latitude, transCoord.longitude);

UTM Coord 6653097.435298, 388455.958023 11
NAD27 Coord 60.000000, -119.000000


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