There is an important difference between the PROJ4 and the PROJ5+ API/syntax:
The old PROJ4 API uses latlong WGS84 as pivot datum for coordinate transformations like projection1 -> latlong WGS84 -> projection2 or in '+to' syntax projection1 +to projection2 The new PROJ5+ API no longer uses a pivot datum. The advantage is that you can directly convert from one datum to another, without going through WGS84. The disadvantage is that the user/software using the new API has to make sure that either a common pivot datum is used or coordinates are correctly transformed from one datum to another, e.g. with a Helmert Transform. Both GDAL and GRASS have implemented the new API as a simple 2-step pipeline like 1. projection1 -> some latlong 2. some latlong -> projection2 or in pipeline syntax +proj=pipeline +step +inv projection1 +step projection2 Even Rouault has done some tests and found sometimes subtle differences in the results between the old and new API/syntax. Further on, there is no mechanism (yet) in place to validate the pipeline, most importantly that the output of step 1 conforms to the required input for step 2. IMHO, the implementation of the new PROJ5+ API/syntax in GDAL and GRASS should be regarded as experimental and testing by as many people as possible would be a huge benefit to PROJ/GDAL/GRASS and to all applications using these projects. Markus M On Sun, Mar 25, 2018 at 10:47 PM, Helmut Kudrnovsky <hel...@web.de> wrote: > > >Now (last related commit is trunk r72522) it's finished. I have >introduced > a new GRASS API that handles both PROJ 4 and PROJ >5, consisting of > > Thanks for this Update! > > Fyi See > https://lists.osgeo.org/pipermail/osgeo4w-dev/2018-March/003557.html > > ------- > [...] > The API from PROJ 4 lives on in PROJ 5, so GRASS 7.4 should be able to use > PROJ 5 as well. We’ve been carefull not to breaking anything with this > release. > That comes with PROJ 6 and 7. Of course there might be implementation > details > in GRASS that I am unaware of that makes using PROJ 5 impossible. > -------- > > > > ----- > best regards > Helmut > -- > Sent from: http://osgeo-org.1560.x6.nabble.com/Grass-Dev-f3991897.html > _______________________________________________ > grass-dev mailing list > grass-...@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-dev
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