<div dir="ltr"><div dir="ltr"><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Sun, 27 Apr 2025 at 21:53, Even Rouault <<a href="mailto:even.rouault@spatialys.com">even.rouault@spatialys.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><u></u>
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<div>During the summit I asked about the interpolation method.
The metadata says that it should be biquadratic. The answer
was: "for the undulation there is almost no difference. But
for other magnitudes, like vertical deflection, it is more
noticeable. However, to match our values you have to do
biquadratic interpolation"</div>
<div>Do we have biquadratic intepolation for the geoid models?</div>
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If you use the generalized +proj=gridshift method, yes, with the
+interpolation=biquadratic flag:
<a href="https://proj.org/en/stable/operations/transformations/gridshift.html#cmdoption-arg-interpolation" target="_blank">https://proj.org/en/stable/operations/transformations/gridshift.html#cmdoption-arg-interpolation</a></div></blockquote><div><br></div><div>Yes, I found that. But it has to be done with directly with the pipeline, right? not with cs2cs. <br></div><div><br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div><br>
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<div>I would be very surprised that they release something at
a different resolution. Some people asked for a GeoTIFF, and
they were reluctant (but not completely oposite). They want
to minimize the different formats and file to deal with (one
ggxf for everything)</div>
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<div>But there are other problems:</div>
<div> - velocities: the full model, considering time
evolution, has a velocity component. N_t = N_2020 + (t-t0) *
v. The resolution of that velocity is different if I checked
correctly. And we do not have such a model in PROJ. (It will
appear in EPSG at some point)</div>
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<p>For difference resolution per file, we already have such case
with us_noaa_nadcon5_nad83_2007_nad83_2011_alaska.tif:</p></div></blockquote><div>Cool. Then adding velocities in the same file will be "easier". <br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>
<p>$ gdalinfo
GTIFF_DIR:1:/home/even/proj/proj-data-1.21/us_noaa_nadcon5_nad83_2007_nad83_2011_alaska.tif<br>
[...]<br>
Origin = (171.958333333333343,73.041666666666671)<br>
Pixel Size = (0.083333333333333,-0.083333333333333)<br>
[...]<br>
Band 1 Block=256x256 Type=Float32, ColorInterp=Gray<br>
Description = latitude_offset<br>
Unit Type: arc-second<br>
Band 2 Block=256x256 Type=Float32, ColorInterp=Undefined<br>
Description = longitude_offset<br>
Unit Type: arc-second<br>
Metadata:<br>
positive_value=east<br>
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<p>$ gdalinfo
GTIFF_DIR:2:/home/even/proj/proj-data-1.21/us_noaa_nadcon5_nad83_2007_nad83_2011_alaska.tif<br>
[...]<br>
Origin = (171.875000000000000,73.125000000000000)<br>
Pixel Size = (0.250000000000000,-0.250000000000000)<br>
[...]<br>
Band 1 Block=241x93 Type=Float32, ColorInterp=Gray<br>
Description = ellipsoidal_height_offset<br>
Unit Type: metre<br>
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<div>One more thing: I do not expect them publishing the intra
frame deformation model (IFDM2022). Every time they
mentioned it they added "Danger!". That leave a feeling of
"incompleteness" among the audience, as that model is needed
for some time dependant transformations (like bringing
measurements to the frame epoch, 2020.0). They will offer it
in their webpage somehow.</div>
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<p>What about NAD83(2011) to NATRF2022: did they mention something ?
Currently PROJ uses NAD83(2011)->ITRF2020 (EPSG:10334) and
ITRF2020->NATRF2022 (using Euler Pole Rotation).</p></div></blockquote><div>They mentioned, but not published (yet). They are doing something called "14H", a collection of Helmert transformations to connect a bunch of reference systems, including all the ITRF*. IIRC, there were like 35 transformations there.</div><div>There was one (named 7A,7B,7C) that was exactly NAD83(2011) to NATRF2022 (I have no idea about the epoch). My hope is that it is equivalent to the concatenation PROJ is doing, but let's see.</div><div>I expect they publish the slides of the summit (not a recording).</div><div><br></div><div>See that at 2020.0, NATRF2022 and ITRF2020 (epoch 2020.0) are identical.</div><div>There was some chaos with the different epochs and transformations available.</div><div>It is going to be fun telling the users (and applications) that now they have to take time into consideration (and do it properly)</div><div> <br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div>
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<pre cols="72">--
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