Oihane Kamara Esteban - 4 months ago 26

Python Question

I've been going around this issue for days, but haven't been able to find an explanation to what I am doing wrong. I hope you can lend me a hand.

I have a set of UTM coordinates

`(epsg:23030)`

`(epsg:4326)`

`(libproj-dev)`

`#include "proj_api.h`

#include <geos/geom/Coordinate.h>

geos::geom::Coordinate utm2longlat(double x, double y){

// Initialize LONGLAT projection with epsg:4326

if ( !( pj_longlat = pj_init_plus("+init=epsg:4326" ) ) ){

qDebug() << "pj_init_plus error: longlat";

}

// Initialize UTM projection with epsg:23030

if ( ! (pj_utm = pj_init_plus("+init=epsg:23030" ) ) ){

qDebug() << "pj_init_plus error: utm";

}

// Transform UTM projection into LONGLAT projection

int p = pj_transform( pj_utm, pj_longlat, 1, 1, &x, &y, NULL );

// Check for errors

qDebug() << "Error message" << pj_strerrno( p ) ;

// Return values as coordinate

return geos::geom::Coordinate(x, y)

}

My call to the function

`utm2longlat`

`...`

// UTM coordinates

double x = 585363.1;

double y = 4796767.1;

geos::geom::Coordinate coord = utm2longlat( x, y );

qDebug() << coord.x << coord.y;

/* Result is -0.0340087 0.756025 <-- WRONG */

In my example:

- I know that
**UTM**coordinatesrefer to`(585363.1 4796767.1)`

**LongLat**coordinates.`(-1.94725 43.3189)`

- However, when called, the function returns a set of wrong coordinates: .
`(-0.0340087 0.756025 )`

I was wondering if I had any misconfiguration when initializing the projections, so I decided to test the Proj4 Python bindings

`(pyproj)`

`from pyproj import Proj, transform`

// Initialize UTM projection

proj_utm = Proj(init='epsg:23030')

// Initialize LongLat projection

proj_lonlat = Proj(init='epsg:4326')

x_utm, y_utm = 585363.1, 4796767.1

x_longlat, y_longlat = transform(proj_utm, proj_lonlat, x_utm, y_utm)

// Print results

print "original", x_utm, y_utm

print "utm2lonlat", x_longlat, y_longlat

/* Result is -1.94725 43.3189 <-- CORRECT */

From what I understand

`pyproj`

`Proj4`

Do you have any clue as to what could be wrong? Am I missing some type of conversion in the C++ function?

Thanks in advance.

Answer

The result seems to be correct to me, but it's returned in radians instead of degrees. Convert the result to degrees and check again.