[Proj] Differences across v4.8 and v4.9

[Even Rouault]

On lundi 28 août 2017 17:46:23 CEST Joaquim Luis wrote:
> Hi,
> 
> I have found these differences between proj.4 versions that I don't find
> any documentation referring them. There is one FAQ
> http://proj4.org/faq.html#why-do-i-get-different-results-with-4-5-0-and-4-6-
> 0 entry but is about differences between 4.5.0 and 4.6.0, whilst this is
> between 4.8 and 4.9.
> 
> The first one (between A1 and B1) is specially more troublesome because is
> the example provide in the cs2cs doc page
> (http://proj4.org/apps/cs2cs.html) that agrees with 4.8.0 and not with
> 4.9.2
> 
> Joaquim
> 
> proj
> Rel. 4.8.0, 6 March 2012
> 
> A1
> echo 45.25919444444 -111.5 | cs2cs +proj=latlong +datum=NAD83 +to
> +proj=utm +zone=10  +datum=NAD27 -r
> 1402285.99      5076292.42 -0.00

I do get this result with proj 4.9.3 too (actually I get 1402285.98	5076292.42 -0.00,
so a slight difference rounding), so I suspect your below 4.9.3 build has been made
without unzipping first the grids at
http://download.osgeo.org/proj/proj-datumgrid-1.6.zip
into the nad/ directory

You can check if grids are used with

echo 45.25919444444 -111.5 | PROJ_DEBUG=ON cs2cs  +proj=latlong +datum=NAD83 +to  +proj=utm +zone=10  +datum=NAD27 -r

You should see towards the end something like

NTv1 393x177: LL=(-142,40) UR=(-44,84)
pj_open_lib(conus): call fopen([...]/share/proj/conus) - succeeded

pj_apply_gridshift(): used Conterminous United States


> 
> A2
> echo 4.897 52.371 | proj +proj=aeqd +ellps=WGS84 +units=m
> 384923.72       5809986.50

Not completely sure about that one when looking at history of
https://github.com/OSGeo/proj.4/commits/master/src/PJ_aeqd.c

Perhaps
https://github.com/OSGeo/proj.4/commit/2d0acd7d61374a167f532cd2851f46f63d5e09a4
or
https://github.com/OSGeo/proj.4/commit/de8d6779aaabe0c46c06b9047bc6a6a978cc0758

> 
> A3
> echo 4.897 52.371 | proj +proj=robin +ellps=WGS84 +units=m
> 394576.51       5571243.64
> 

I suspect the difference comes from
https://github.com/OSGeo/proj.4/commit/d856016ca1a178cc81c4474c0a6bbe78d106d012

I agree the https://github.com/OSGeo/proj.4/blob/master/NEWS don't mention this case nor A2.

-- 
Spatialys - Geospatial professional services
http://www.spatialys.com
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