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Use perspective transform for datasets with 4 GCPs #11940

@NathanMOlson

Description

@NathanMOlson

Feature description

Currently, when there are 1-5 GCPs in a dataset, GDALCreateGenImgProjTransformer2() uses the GCP_POLYNOMIAL transform with order 1. This does not provide an exact match at all GCPs if there are 4 or more GCPs present. A perspective transform would provide an exact match at 4 GCPs.

I propose a new transform type HOMOGRAPHY that would be selected if there are exactly 4 (and possibly 5) GCPs in a dataset.

Additional context

The impetus for this change is to improve the display of 4-corner GeoTIFFs in QGIS.

qgis/QGIS#60898

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