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diff --git a/docs/source/glossary.rst b/docs/source/glossary.rst index 21dd0f34..883460d4 100644 --- a/docs/source/glossary.rst +++ b/docs/source/glossary.rst @@ -6,6 +6,25 @@ Glossary .. glossary:: + Ballpark transformation + + For a transformation between two geographic CRS, a ballpark + transformation is a coordinate operation that only takes into account + potential difference of axis orders (long-lat vs lat-long), + units (degree vs grads) and prime meridian (Greewich vs Paris/Rome/other + historic prime meridians). It does not attempt any datum shift, hence + the "ballpark" qualifier in its name. Its accuracy is unknown, and could + lead in some cases to errors of a few hundreds of metres. + + For a transformation between two vertical CRS or a vertical CRS and + a geogrpahic CRS, a ballpark transformation only takes into account + potential different in units (e.g. metres vs feet). Its accuracy is + unknown, and could lead in some cases to errors of a few tens of metres. + + .. note:: + + The term "Ballpark transformation" is specific to PROJ. + Pseudocylindrical Projection Pseudocylindrical projections have the mathematical characteristics of |