Opened 9 years ago

Closed 9 years ago

#3737 closed defect (fixed)

NAD27 expands to use towgs84 instead of grid shift files

Reported by: warmerdam Owned by: warmerdam
Priority: normal Milestone:
Component: OGR_SRS Version: unspecified
Severity: normal Keywords: nad27
Cc: Even Rouault

Description (last modified by warmerdam)

For reasons that are not clear, the expansion of "NAD27" in OGRSpatialReference::SetWellKnownGeogCS() has include a TOWGS84[] approximation in the WKT for a very long time.

With the introduction of r19903 the translation of the WKT to PROJ.4 format uses a +towgs84 parameter instead of the +nadgrids directive (previously implicit from +datum).

On a related note the current expansion of EPSG:4267 (NAD27) uses a towgs84 value from the datum_shift.csv.

Change History (2)

comment:1 Changed 9 years ago by warmerdam

Description: modified (diff)

comment:2 Changed 9 years ago by warmerdam

Resolution: fixed
Status: newclosed

Several related changes made. First libgeotiff's build_pcs.py was adjusted to avoid putting a towgs84 parameter in for NAD27 (http://trac.osgeo.org/geotiff/changeset/1889).

Changes to ensure +datum=NAD27 is used if there is no TOWGS84 parameter applied in trunk (r20501) along with changes to avoid putting out +ellpse if +datum is present and removing TOWGS84 from the well known expansion of NAD27. A few test suite changes made related to this also in trunk (r20500).

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