[PROJ] How to apply Helmert trafo

Lesparre, Jochem Jochem.Lesparre at kadaster.nl
Mon Jun 17 00:30:52 PDT 2019

Dear Fabian,

For this transformation push/pop is not needed. That only makes sense in other situations, like when you use a geoid.

If the scale factor also differs from the primary source (EPSG is a secondary source), it should be adapted in the example to avoid confusion. If EPSG differs with the primary source, EPSG should be notified that there might be a mistake in their registry.

Kind regards, Jochem

From: PROJ <proj-bounces at lists.osgeo.org> On Behalf Of Fabian Gross
Sent: Friday, June 14, 2019 3:41 PM
To: proj at lists.osgeo.org
Subject: [PROJ] How to apply Helmert trafo

Dear proj-members,

I would like to apply a Helmert trafo as part of a datum shift.
The example follows the EPSG geomatics guidance 7/2 (report 373-7-2):

From WGS72 (4984) -> WGS84 (4978).

There are 2 issues:
1. How to apply Helmert-Trafo? I.e.

  *   with or
  *   without the push/pop of the ellipsoidal height.
Only if it is not pushed/popped do the values fit to the reference and the direct/naive implementation of Helmert.
2. The scale parameters in the example (0.219) and the EPSG catalogue of pyproj (0.2263)  do not agree.

The attached file has the test case.

Kind regards

Fabian Gross
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