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| author | Even Rouault <even.rouault@spatialys.com> | 2020-04-04 13:17:02 +0200 |
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| committer | Even Rouault <even.rouault@spatialys.com> | 2020-04-04 13:17:02 +0200 |
| commit | ef3a387abd5989f6d5242a6c8cd0f7b6e7318484 (patch) | |
| tree | de97cf09f722c4e819eed4dccc0e3aee4791bda7 | |
| parent | 99a2d5f248b828ff97121b0137569a0094b5c63e (diff) | |
| download | PROJ-ef3a387abd5989f6d5242a6c8cd0f7b6e7318484.tar.gz PROJ-ef3a387abd5989f6d5242a6c8cd0f7b6e7318484.zip | |
Doc: define 'Ballpark transformation'
| -rw-r--r-- | docs/source/glossary.rst | 19 | ||||
| -rw-r--r-- | docs/source/operations/operations_computation.rst | 7 |
2 files changed, 21 insertions, 5 deletions
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 diff --git a/docs/source/operations/operations_computation.rst b/docs/source/operations/operations_computation.rst index ef84cfb2..2f532127 100644 --- a/docs/source/operations/operations_computation.rst +++ b/docs/source/operations/operations_computation.rst @@ -106,11 +106,8 @@ which can be used as an override). As those results all involve operations that does not have a perfect accuracy and that does not cover the area of use of the 2 CRSs, a -'Ballpark geographic offset from NAD27 to NAD83' operation is synthetized by PROJ. -This operation is a sort of dummy 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. +'Ballpark geographic offset from NAD27 to NAD83' operation is synthetized by PROJ +(see :term:`Ballpark transformation`) Filtering and sorting of coordinate operations ---------------------------------------------- |