[Proj] Error during the coordinate transformation?

Fernando Javier Luyo Zegarra fluyoz at hotmail.com
Wed Apr 1 14:32:47 EST 2009

The code corresponds to Perú

Date: Tue, 31 Mar 2009 16:17:29 -0500
From: cjmce at lsu.edu
To: proj at lists.maptools.org; proj at lists.maptools.org
Subject: Re: [Proj] Error during the coordinate transformation?

Dear Fernando:
What country is this, and what parameters did you use.  I suspect you're in Venezuela ... please confirm.
Estan usted en la Republica de Venezuela?  Esta verdad?
C. Mugnier
Louisiana State University

From: proj-bounces at lists.maptools.org on behalf of Fernando Javier Luyo Zegarra
Sent: Tue 31-Mar-09 16:11
To: proj at lists.maptools.org
Subject: [Proj] Error during the coordinate transformation‏


I'm developed a routine for transforming coordinates of points which are in PSAD56 Zone 18S (srid = 24878) to Wgs84 Zone 18s (srid = 32718)

The items are stored in the fields "geom" the table "MyTable" (srid = 24878).

To perform the operation using the following syntax:

       select Transform (geom, 32718) from MyTable

Reviewing the results found that there is an error:


Point in Psad56 Zn 18s

        X = 264365.2955 Y = 8665287.3660 Z = 0.0000

The result of the transformation is:

        X = 264366.1196 Y = 8665292.17 Z = 0.0000

However, the same point in cartografia WGS84 Zone 18S has the following coordinates:

        X = 264143.0640 Y = 8664919.0231 Z = 0.0000

Apparently the SRID of the parameters are not properly used or applied incorrectly the function Transform ()

While waiting for your help

Fernando Luyo
pd: Sorry for my bad English


Estoy elaborando una rutina para transformar coordenadas de puntos que estan en PSAD56 Zona 18S (srid=24878) a Wgs84 Zona 18s (srid=32718)

Los puntos estan almacenados en el campo "geom" de la tabla "MyTable" (srid=24878).

Para realizar la operacion estoy usando la siguiente sintaxis:

select Transform(geom,32718) from MyTable

Al revisar los resultados encontre que hay un error :

Ejemplo : 

Punto en Psad56 Zn 18s

X = 264365.2955     Y = 8665287.3660     Z = 0.0000

El resultado de la transformacion es: 

X = 264366.1196     Y = 8665292.17       Z = 0.0000

Sin embargo, el mismo punto en cartografia en WGS84 Zona 18S tiene las siguientes coordenadas:

X = 264143.0640     Y = 8664919.0231     Z = 0.0000

Al parecer los parametros de los SRID usado no estan correctos o estoy aplicando mal la funcion Transform()

A la espera de su ayuda< br>

Fernando Luyo


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