[mapserver-dev] RFC 126: Port to PROJ 6 API

[Seth G]

One last question - will it still be possible to use inline projection parameters as in the examples at https://mapserver.org/mapfile/projection.html#projections-with-mapserver ? If so would this avoid a call to proj.db?

Seth


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On Wed, Oct 2, 2019, at 1:14 PM, Even Rouault wrote:
> On mercredi 2 octobre 2019 12:44:05 CEST Seth G wrote:
> > Hi Even,
> > 
> > Great news getting PROJ6 integrated.
> > 
> > A couple of questions.
> > 
> > - Should Appveyor be updated to also test on Windows? I believe the
> > GISInternals SDK has a bin/proj6 folder already.
> 
> That could. I always struggle with Appveyor/Windows, so I'd happily let that 
> as an exercice for other contributors :-) (I don't anticipate any particular 
> issue specific to Windows compilation)
> 
> > 
> > - With regards to start up performance/CGI I presume there is no impact if
> > all source data is in the same projection as the request e.g. all data in
> > the database is EPSG:3857 and Web Mercator requests are made. It might be a
> > case of making sure users are aware of the impact of having to reproject.
> 
> There might be an impact even if there is no reprojection, especially if 
> working with EPSG codes, because you still have to instanciate a projection 
> object, and whatever you use PROJ 4 or PROJ 6 API, with PROJ 6, resolving a 
> EPSG code will go through the proj.db
> 
> I've just done a little experiment by modifying my bench to use EPSG:4326 
> everywhere:
> - for one iteration, with PROJ 4 API: 11 ms/iter. With PROJ 6 API: 10 ms/iter
> - for 500 iterations, with PROJ 4 API: 0.8 ms/iter. PROJ 6 API: 0.9 ms/iter
> 
> I'm not sure why the PROJ 6 single iteration is a little faster than the PROJ 
> 4 one
> 
> Another data point is that if I bench against PROJ 5.1 (so using PROJ 4 API), 
> I get 5 ms for the single iteration case (and 0.8 ms/iter for the 500 
> iteration cases). So there's an additional cost using PROJ 6 in a single 
> iteration case, whatever API you use. This is clearly related to querying the 
> database and constructing a in-memory GeographicCRS PROJ object, whereas PROJ 
> < 6 would just load a pre-baked PROJ string.
> 
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