[Proj] Differences in reprojection between using the cs2cs app and using the api

[Hermann Peifer]

Adri,

Just to confirm that using the API doesn't make any difference, as 
expected. See mycode.c below, based on 
https://trac.osgeo.org/proj/wiki/ProjAPI

Your own sample code below has these coordinates:
 > /double lat = -45.491596;
 > /double lon = -23.570147;

This point falls into the South Atlantic Ocean, somewhere in the middle 
between Tierra del Fuego and Cape Town. So you'd have to swap lat/lon in 
order to get to the Rodovia dos Tamoios, (SP-099).

Hope this helps, Hermann

$ echo -45.491596 -23.570147 769.750000 | ./mycode
449834.145105	7393276.784821	769.75

$ cat mycode.c
#include <stdio.h>
#include <proj_api.h>

int main(int argc, char **argv) {

	projPJ wgs, sirgas;
	double lon, lat, alt;

	if (!(wgs = pj_init_plus("+init=epsg:4326")) )
		exit(1);

	if (!(sirgas = pj_init_plus("+init=epsg:31983")) )
		exit(1);

	while (scanf("%lf %lf %lf", &lon, &lat, &alt) == 3) {
		lon *= DEG_TO_RAD;
		lat *= DEG_TO_RAD;
		pj_transform(wgs, sirgas, 1, 1, &lon, &lat, &alt);
		printf("%.6f\t%.6f\t%.2f\n", lon, lat, alt);
	}
	exit(0);
}


On 2015-02-11 18:07, Adri CS wrote:
> Hi,
>
> I built Proj4 4.8.0 for Windows with MinGW. I'm trying to reproject some
> WGS84 lat/long coordinates (degrees) from Brazil to UTM Sirgas 2000. The
> UTM zone would be 23S.
>
> **) Using the cs2cs app:
>
> /cs2cs.exe -f %.6f +init=epsg:3273 +proj=latlong +to +init=epsg:31938
> input.txt > output.txt/
>
> **The input file would contain coords like this: -45.491596
> -23.570147 769.750000
>
> And the output would be: 449834.145105    7393276.784821 769.750000
>
> /***********************************************/
>
> **) Using the api (I omit the error checking):
>
> /projPJ wgs = pj_init_plus("+init=epsg:32723 +proj=latlong");
> /
> /projPJ sirgas = = pj_init_plus("+init=epsg:31983");
> /
> /double lat = -45.491596;
> /
> /double lon = -23.570147;
> double alt = 769.750000;
>
> /
> /lat *= DEG_TO_RAD;
> /
> /lon *= DEG_TO_RAD;
> /
> /
> /
> /pj_transform(wgs, sirgas, 1, 1, &lon, &lat, &alt);/
>
> This outputs: 449834.127632      7393276.821296       769.750000
>
> In both cases, the left part of the returned UTM easting and northing
> coordinates are the same, but the numbers after the decimal point are
> different.
>
> I'm only transforming the input lat/lon coordintates when using the api,
> since if I transform them before calling cs2cs, it will output wron
> coords (the easting will have 7 digits before the decimal points).
>
> What's happening here? The only difference I can see it's the
> transformation of the lat/lon coordinates from degrees to radians: I'm
> multypling directly while in the cs2cs source, there's a call to the
> /dmstor/ function (which I can't call directly, it seems).
>
> Thanks for your time & cheers!
> Adri.
>
>
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