<div dir="ltr"><div dir="ltr">Hello, thank you very much for your kindness and for your time.<br><br>Happy New Year<br><br>Eddison<br><br><br><br></div><br><img width="0" height="0" class="mailtrack-img" alt="" style="display:flex" src="https://mailtrack.io/trace/mail/36a29022d59fc76ea9611f58ab0241bb974a8685.png?u=5552924"><div class="gmail_quote"><div dir="ltr" class="gmail_attr">El mar, 3 ene 2023 a las 18:42, Nicolas Cadieux (<<a href="mailto:njacadieux.gitlab@gmail.com">njacadieux.gitlab@gmail.com</a>>) escribió:<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>Hi,</p>
<p>I looked at vdatum and could not find how to remove an
ellipsoidal. Apparently, this software can only translate from
one ellipsoid to another but cannot simply remove the ellipsoid.
I would use Ujaval's method as this will faster to figure out then
what I originally did. You can also get help from the gdal
developers. <br>
</p>
<p>You may use the unavco page to get more information and to double
check your results. <br>
</p>
<p><a href="https://www.unavco.org/software/geodetic-utilities/geoid-height-calculator/geoid-height-calculator.html" target="_blank">https://www.unavco.org/software/geodetic-utilities/geoid-height-calculator/geoid-height-calculator.html</a></p>
<p>You may also look at the GPS H tool (online and pc version) from
NRCAN. You need to create a profile if you want to download the
software. Unfortunately, this tool only works with point data but
the PC version can read geoid files from Noaa. I used that to
double check my results. To remove an ellipsoid, use GPS H using
the h=H+N mode using an input height of 100.0m.</p>
<p>To test (with geoid model HT2_0), for a point situated at 50°N
and 100°W if a geoid height or topographic height (H) of 100m,
the ellipsoid (N) will be at -23.434 meters and the height (h)
above the ellipsoid at 76.566m. I would first try to reproduce
using HT2_0 that comes with GPS H. Then, use the EGM96 downloaded
from NOAA. Finally, test using to top left pixel of your image.
<br>
</p>
<p>Once you transform the image using gdalwarp, look at the value of
your top left pixel to see if it matches what you get from GPS H.
Warning... this software uses GRS80 Ellipsoid. I think ALOS uses
GRS80 but if it's the WGS84 ellipsoid, you will see very small
differences (probably sub-millimeter.) I would not worry at this
point. <br>
</p>
<p>Nicolas<br>
</p>
<p><img src="cid:185854081c066f7ed7f1"></p>
<div>On 2023-01-03 12:54 a.m., Ujaval Gandhi
wrote:<br>
</div>
<blockquote type="cite">
<div dir="auto">I have a blog post explaining how to do the
conversion using GDAL
<div dir="auto"><a href="https://spatialthoughts.com/2019/10/26/convert-between-orthometric-and-ellipsoidal-elevations-using-gdal" target="_blank">https://spatialthoughts.com/2019/10/26/convert-between-orthometric-and-ellipsoidal-elevations-using-gdal</a></div>
</div>
<div><br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, 3 Jan 2023 at 11:09
AM, Eddison Araya via QGIS-User <<a href="mailto:qgis-user@lists.osgeo.org" target="_blank">qgis-user@lists.osgeo.org</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">
<div dir="ltr">
<div dir="ltr">Hi, thanks, skip previous message,
apparently you're right, it's emg96<br>
<br>
Thank you<br>
<br>
Eddison<br>
<br>
<img src="cid:185854081c0cb971f162" alt="image.png" style="width: 844px; max-width: 100%; background-color: rgba(0, 0, 0, 0); border-color: rgb(255, 255, 255); color: rgb(255, 255, 255);"><br>
<br>
<br>
</div>
<br>
<img alt="" style="display: flex;" src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" width="0" height="0"></div>
<div dir="ltr">
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">El lun, 2 ene 2023 a
las 20:08, Eddison Araya (<<a href="mailto:eddisonjose@gmail.com" target="_blank">eddisonjose@gmail.com</a>>)
escribió:<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 dir="ltr">
<div dir="ltr"><br>
Hello yes, thank you very much, according to that
source it is EMG-2008<br>
<br>
Regards!<br>
<br>
eddison<br>
<br>
<img src="cid:185854081c0cb971f163" alt="image.png" style="width: 334px; max-width: 100%; background-color: rgba(0, 0, 0, 0); border-color: rgb(255, 255, 255); color: rgb(255, 255, 255);"><br>
<br>
<br>
</div>
<br>
<img alt="" style="display: flex;" width="0" height="0" src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7">
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">El lun, 2 ene
2023 a las 11:16, Nicolas Cadieux (<<a href="mailto:njacadieux.gitlab@gmail.com" target="_blank">njacadieux.gitlab@gmail.com</a>>)
escribió:<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 dir="auto">Hi,
<div><br>
<div>Will do. I’am heading out of the woods
now. In the mean time, look at the
metadata to find out what ellipsoid is
being used by the file. I believe it’s
probably EMG96 but can you confirm? <br>
<br>
<div dir="ltr">Nicolas Cadieux
<div><a href="https://gitlab.com/njacadieux" target="_blank"><span id="m_-6403055564024416847m_3694107932837509714mt-tracked-link_1672724305583" style="color:red"></span>https://gitlab.com/njacadieux</a></div>
</div>
<div dir="ltr"><br>
<blockquote type="cite">Le 2 janv. 2023
à 08:01, Eddison Araya <<a href="mailto:eddisonjose@gmail.com" target="_blank">eddisonjose@gmail.com</a>>
a écrit :<br>
<br>
</blockquote>
</div>
<blockquote type="cite">
<div dir="ltr">
<div dir="ltr">
<div dir="ltr">Hello Nicolás
Cadieux, I hope you had a nice end
and beginning of the year!<br>
<br>
Ok very good, so I await your
message with the step by step,
just in case I attach the image:
<div><br>
<br>
<a href="https://drive.google.com/file/d/1mJvB77MMOF86X7I4qwtS3i7UYq1wYmGR/view?usp=share_link" target="_blank"><span id="m_-6403055564024416847m_3694107932837509714mt-tracked-link_1672724305585" style="color:red"></span>https://drive.google.com/file/d/1mJvB77MMOF86X7I4qwtS3i7UYq1wYmGR/view?usp=share_link</a></div>
<div><br>
<br>
Greetings and thank you very
much<br>
<br>
Eddison<br>
<br>
<br>
<br>
</div>
</div>
<br>
<img alt="" style="display: flex;" width="0" height="0" src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7"><img alt="" style="display: flex;" width="0" height="0" src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7">
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">El
jue, 29 dic 2022 a las 21:11,
Nicolas Cadieux (<<a href="mailto:njacadieux.gitlab@gmail.com" target="_blank">njacadieux.gitlab@gmail.com</a>>)
escribió:<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 dir="auto">Hi,
<div><br>
<div>Google vdatum <a href="https://vdatum.noaa.gov/" target="_blank"><span id="m_-6403055564024416847m_3694107932837509714mt-tracked-link_1672724305586" style="color:red"></span>https://vdatum.noaa.gov/ </a> Contact
me early next year and I
can help you step by
step. I can’t help you
more now because i’am far
from civilisation with
very limited internet
access.</div>
<div><br>
<div dir="ltr">Nicolas
Cadieux
<div><a href="https://gitlab.com/njacadieux" target="_blank"><span id="m_-6403055564024416847m_3694107932837509714mt-tracked-link_1672724305587" style="color:red"></span>https://gitlab.com/njacadieux</a></div>
</div>
<div dir="ltr"><br>
<blockquote type="cite">Le
28 déc. 2022 à 09:52,
Eddison Araya via
QGIS-User <<a href="mailto:qgis-user@lists.osgeo.org" target="_blank">qgis-user@lists.osgeo.org</a>> a
écrit :<br>
<br>
</blockquote>
</div>
<blockquote type="cite">
<div dir="ltr">
<div dir="ltr">Hello,
a pleasure to greet
you.<br>
<br>
I need to convert an
ALOS PALSAR DEM from
ellipsoidal to
geoid.<br>
<br>
Does anyone know how
to do this process
step by step?<br>
<br>
Thank you<br>
<br>
Eddison<br>
<br>
<br>
<br>
<img alt="" style="display: flex;" width="0" height="0" src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7"></div>
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-- <br>
<div dir="ltr">
<div dir="ltr">---
<div>Ujaval Gandhi</div>
<div>Spatial Thoughts</div>
<div><a href="http://www.spatialthoughts.com" target="_blank">www.spatialthoughts.com</a></div>
<div><br>
</div>
</div>
</div>
</blockquote>
<pre cols="72">--
Nicolas Cadieux
<a href="https://gitlab.com/njacadieux" target="_blank">https://gitlab.com/njacadieux</a></pre>
</div>
</blockquote></div></div>