[Proj] Error during the coordinate transformation‏

[Frank Warmerdam]

Fernando Javier Luyo Zegarra wrote:
> 
> Hello,
> 
> 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:
> 
> 
> Example:
> 
> 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 ()

Fernando,

I would encourage you to determine what PROJ.4 init strings are associated
with 32718 and 24878.  It looks like there is a missing or incorrect datum
shift being applied.

Best regards,
-- 
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