# [Proj] False Easting & Northing for LAEA?

Bob Fischer robert.p.fischer-1 at nasa.gov
Mon Apr 9 09:06:07 EST 2012

```Hello,

I'm pretty new to Proj.4.  I'm having a bit of trouble with false
easting and northing.  See code below (using a simple C++ wrapper):

const double D2R = M_PI / 180.0;

double proj_lon_0 = -40;
double proj_lat_0 = 74;
char sproj[100];
sprintf(sproj, "+proj=laea +lon_0=%f +lat_0=%f +x0=1000000
+y0=1700000 +ellps=sphere",
proj_lon_0, proj_lat_0);
printf("Using projection: \"%s\"\n", sproj);
Proj proj(sproj);
printf("Using full projection: \"%s\"\n", proj.get_def().c_str());

The output is:

Using projection: "+proj=laea +lon_0=-40.000000 +lat_0=74.000000
+x0=1000000 +y0=1700000 +ellps=sphere"
Using full projection: " +proj=laea +lon_0=-40.000000 +lat_0=74.000000
+ellps=sphere"

Note that my false easting/northing has been removed from my proj.4
string!  The fact that no false easting/northing is being used is
confirmed when I try to transform a point:

double lon00 = -40;
double lat00 = 74;
double xp,yp;
int err = transform(llproj, proj, lon00*D2R, lat00*D2R, xp, yp);
printf("Proj.4 transform 00 -> (%f, %f) (err = %d)\n", xp, yp, err);

Output is:

Proj.4 transform 00 -> (0.000000, -0.000000) (err = 0)

Any ideas on why I'm not getting a false easting/northing here?  I can
certainly work around the problem, but it would be nice if it could work.

Thanks!
-- Bob

(C++ wrapper is included below, for reference)

/** C++ API for proj.4 Projection Library.
Copyright (c) 2012 by Robert Fischer: robert.fischer at nasa.gov
April 5, 2012

Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the "Software"),
to deal in the Software without restriction, including without limitation
the rights to use, copy, modify, merge, publish, distribute, sublicense,
and/or sell copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
*/

#ifndef PROJPP_HPP
#define PROJPP_HPP

#include <proj_api.h>

#if 0
class ProjContext;

class ProjStatic {
public:
ProjContext const defaultContext;

ProjStatic();
};
extern ProjStatic projStatic;

class ProjContext {
projCtx ctx;

public :

};

#endif

namespace giss {

class Proj {
projPJ pj;

explicit Proj(projPJ _pj) : pj(_pj) {}

public:
friend int transform(Proj const &src, Proj const &dest,
long point_count, int point_offset,
double *x, double *y, double *z);

// ------------------ Five Standard constructors/methods
// See: http://www2.research.att.com/~bs/C++0xFAQ.html

explicit Proj(std::string const &definition)
{
pj = pj_init_plus(definition.c_str());
// pj_def = 0;
}

explicit Proj(char const *definition)
{
pj = pj_init_plus(definition);
}

~Proj()
{
pj_free(pj);
// if (pj_def) pj_dalloc(pj_def);
}

/** Transfer ownership */
Proj(Proj&& h) : pj{h.pj} //, pj_def{h.pj_def}
{
h.pj = 0;
// h.pj_def = 0;
}

/** Transfer value */
Proj& operator=(Proj&& h) = delete;

/** Copy constructor */
Proj(const Proj &h)
{
char *pj_def = pj_get_def(h.pj, 0);
pj = pj_init_plus(pj_def);
pj_dalloc(pj_def);
}

// no copy with operator=()
Proj& operator=(const Proj&) = delete;

// --------------------------- Other Stuff

/** Returns TRUE if the passed coordinate system is geographic
(proj=latlong). */
int is_latlong() const
{ return pj_is_latlong(pj); }

/** Returns TRUE if the coordinate system is geocentric
(proj=geocent). */
int is_geocent() const
{ return pj_is_geocent(pj); }

/** Returns the PROJ.4 initialization string suitable for use with
pj_init_plus() that would produce this coordinate system, but with the
definition expanded as much as possible (for instance +init= and
+datum= definitions).
@param options Unused at this point
*/
std::string get_def(int options=0) const
{
char *pj_def = 0;
pj_def = pj_get_def(pj, options);

std::string ret = std::string(pj_def);
pj_dalloc(pj_def);
return ret;
}

/** Returns a new coordinate system definition which is the geographic
coordinate (lat/long) system underlying pj_in. */
Proj latlong_from_proj() const
{
return Proj(pj_latlong_from_proj(pj));
}

};

inline int transform(Proj const &src, Proj const &dest,
long point_count, int point_offset, double *x, double *y, double *z=0)
{
return pj_transform(src.pj, dest.pj,
point_count, point_offset, x, y, z);
}

inline int transform(Proj const &src, Proj const &dest,
double x0, double y0, double &x1, double &y1)
{
x1 = x0;
y1 = y0;
int ret = transform(src, dest, 1, 1, &x1, &y1);
return ret;
}

}

#endif

```