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| -rw-r--r-- | docs/source/operations/operations_computation.rst | 18 |
1 files changed, 15 insertions, 3 deletions
diff --git a/docs/source/operations/operations_computation.rst b/docs/source/operations/operations_computation.rst index 0bc57ff0..5c2596e6 100644 --- a/docs/source/operations/operations_computation.rst +++ b/docs/source/operations/operations_computation.rst @@ -59,9 +59,9 @@ From a code point of view, the entry point of the algorithm is the C++ It combines several strategies: -- look up in the PROJ database for available operations -- consider the pair (source CRS, target CRS) to synthetize operations depending - on the nature of the source and target CRS. + - look up in the PROJ database for available operations + - consider the pair (source CRS, target CRS) to synthetize operations depending + on the nature of the source and target CRS. Geographic CRS to Geographic CRS, with known identifiers -------------------------------------------------------- @@ -156,6 +156,18 @@ performed in the order they are listed below: lexicographic order (e.g. "FOO to BAR (3)" will have higher precedence than "FOO to BAR (2)") +.. note:: + + :c:func:`proj_trans`, on the results returned by :c:func:`proj_create_crs_to_crs`, + will not necessarily use the operation that + is listed in first position due to the above algorithm. :c:func:`proj_trans` + has more context, since it has the coordinate to transform, so it can compare + this coordinate to the area of use of operations. Typically, the above criteria + will favor an operation that has a larger area of use over another one with a + smaller area, due to it being more generally applicable. But once coordinates are known, + :c:func:`proj_trans` can select an operation with a smaller + area of use that applies to the coordinate to transform. + Geodetic/geographic CRS to Geodetic/geographic CRS, without known identifiers ----------------------------------------------------------------------------- |