Problem with transforming coordinate systems

Question

Hiho,
i've got a problem with transforming coordinate systems.
When I'm trying to transform a sdo_geometry object to another coordinate sytem and then back to the old system, the coordinates are not the same.
Here's an example:
StartSystem SRID is 8220 (Longitude / Latitude (DHDN))
TargetSystem SRID is 8307 (Longitude / Latitude (WGS84))
Original object:
Polygon: {ExteriorRing: LineString: { (0.0, -90.0) (1.5, 0.0) (0.0, 90.0) (4.5, 0.0) (0.0, -90.0)} }
Transformed object:
Polygon: {ExteriorRing: LineString: { (0.0, -5156.620156177403) (85.94366926962347, 0.0) (0.0, 5156.620156177403) (257.8310078088704, 0.0) (0.0, -5156.620156177403)} }
Transformed back to old system:
Polygon: {ExteriorRing: LineString: { (0.0, -5156.620156177403) (4924.209525017614, 0.0) (0.0, 5156.620156177403) (14772.628575052844, 0.0) (0.0, -5156.620156177403)} }
Any ideas what to do?
Thanks for the help in advance.
Dirk

Answer 1

Hi Dirk
Since the transform you are trying to do is just a datum conversion of lat./long. coordinates, even the first transform yields obvious rubbish. What you have provided here does not illustrate how you submitted your polygon to CS_TRANSFORM.
Provide the syntax of your construction of the corresponding SDO_GEOMETRY object and your SQL select statement that gave these results.
Bruce