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<p>It would also be interested to check how this affects our
compliance with the GIGS test suite (<a class="moz-txt-link-freetext" href="https://gigs.iogp.org/">https://gigs.iogp.org/</a>)</p>
<p>For example the tests for LAEA are at
<a class="moz-txt-link-freetext" href="https://github.com/IOGP-GIGS/GIGSTestDataset/blob/main/GIGSTestDatasetFiles/GIGS%205100%20Conversion%20test%20data/ASCII/GIGS_conv_5110_LAEA_output.txt">https://github.com/IOGP-GIGS/GIGSTestDataset/blob/main/GIGSTestDatasetFiles/GIGS%205100%20Conversion%20test%20data/ASCII/GIGS_conv_5110_LAEA_output.txt</a></p>
<p>Currently we perfectly reproduce the expected results of GIGS at
the millimeter level, although the test suite asks only for a 0.05
m tolerance<br>
</p>
<p>$ echo 70 5 | bin/cs2cs -d 3 EPSG:4258 EPSG:3035<br>
5214090.649 4127824.658 0.000<br>
$ echo 60 5 | bin/cs2cs -d 3 EPSG:4258 EPSG:3035<br>
4109791.660 4041548.125 0.000<br>
$ echo 50 5 | bin/cs2cs -d 3 EPSG:4258 EPSG:3035<br>
2999718.853 3962799.451 0.000<br>
$ echo 40 5 | bin/cs2cs -d 3 EPSG:4258 EPSG:3035<br>
1892578.962 3892127.020 0.000<br>
$ echo 30 5 | bin/cs2cs -d 3 EPSG:4258 EPSG:3035<br>
796781.677 3830117.902 0.000<br>
$ echo 52 10 | bin/cs2cs -d 3 EPSG:4258 EPSG:3035<br>
3210000.000 4321000.000 0.000<br>
$ echo 50 0 | bin/cs2cs -d 3 EPSG:4258 EPSG:3035<br>
3036305.967 3606514.431 0.000<br>
$ echo 50 3 | bin/cs2cs -d 3 EPSG:4258 EPSG:3035<br>
3011432.894 3819948.288 0.000<br>
</p>
<p>The formulas for LAEA in the EPSG guidance node 7-2 use the
3-term series based on square eccentricy, which is the current one
of PROJ</p>
<p>That said, when runnings the corresponding test file converted to
be used by PROJ's "gie" test, we do pass the simple one-time
forward / reverse tests, but not repeated 1000 times where a 6mm
drift is tolerated and we are currently at ~300 to ~1300
millimeters. Perhaps using those more precise formulas will help
improve the repeated round-tripping.<br>
</p>
<p>Cf <a class="moz-txt-link-freetext" href="https://github.com/OSGeo/PROJ/pull/4247">https://github.com/OSGeo/PROJ/pull/4247</a> for the details (as
the tests don't pass, the test file is not run by the automated
test suite, so it must be run manually as shown in the PR).<br>
</p>
<p>Even<br>
</p>
<div class="moz-cite-prefix">Le 11/09/2024 à 11:30, Even Rouault via
PROJ a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:af32ee83-de40-4683-af38-b8a61db0bcca@spatialys.com">
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<br>
<blockquote type="cite"
cite="mid:2928b861-f54f-42ed-90f0-94ba7eff3ec6@ecere.com">
<div class="moz-signature"> We will surely find out when we run
the unit tests for those projections?</div>
</blockquote>
<p>Not sure which tolerance they have and how much those
projections are tested (do not forget that much of the
regression test suite was automatically generated with the
results PROJ produced at that time, so with quite generic
tolerances, etc.). I was more thinking about manually testing
with proj/cct binaries before and after, and see the differences<br>
</p>
<blockquote type="cite"
cite="mid:2928b861-f54f-42ed-90f0-94ba7eff3ec6@ecere.com">
<div class="moz-signature"><br>
</div>
<div class="moz-signature">
<blockquote type="cite">
<p>It is also not immediately obvious to me to correlate
your proposed code with the formulas in the paper by just
starring at both at the same time. Looks like some
"interpretation" of the paper has been done. </p>
</blockquote>
</div>
<div class="moz-signature">It's quite straightforward, but
optimized for the precalculations like PROJ was doing in <i>auth.cpp</i>.
There is no "interpretation" involved.<br>
</div>
</blockquote>
Well, what you mention below is what I call "interpretation", that
is not direct copying of ready-made formulas, where someone
unqualified could trivially check if there's no typo ;-)<br>
<blockquote type="cite"
cite="mid:2928b861-f54f-42ed-90f0-94ba7eff3ec6@ecere.com">
<div class="moz-signature"> </div>
<br>
<div class="moz-signature"><br>
</div>
<div class="moz-signature">It is of course still possible that I
made a mistake with all this, but I imagine that updating this
and running the tests should help to be confident about the
results.<br>
</div>
</blockquote>
<p>Running the existing PROJ test suite will show if the new
formulas are consistent with the current less precise ones with
maybe a quite loose tolerance, not necessarily that we reach the
new level of precision we claim. Hence comparing with some
random test points against GeographicLib which can hopefully be
considered as a reference implementation, to check we have
identical results (or at least share more common decimals up to
the desired precision)</p>
<br>
<pre class="moz-signature" cols="72">--
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moz-do-not-send="true">http://www.spatialys.com</a>
My software is free, but my time generally not.</pre>
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</blockquote>
<pre class="moz-signature" cols="72">--
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My software is free, but my time generally not.</pre>
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