I'm trying to reproject some data from one CRS to another (SRID:27493 to SRID:3763) using the SDO_CS.TRANSFORM function.

The function works and returns no errors, but the coordinate transformation function that Oracle is using must be inadequate, because the results area inaccurate.

So, I would like to alter or define a new coordinate transformation function that suits my data.

I've realized that in the SDO_COORD_REF_SYS table there is an PROJECTION_CONV_ID attribute that should lead somewhere, but the transformation function and its parameters seem to be dispersed through several tables.

Anyone has experience in this and / or can point some manuals / tutorials?

Search for Spatial Developer Guide Chapter 6.9.6 Creating a Transformation Operation

Chapter 6.9.7 contains an example how to change the trans formation based of helmert parameter to ntv2

this is the current link for Release 18

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