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    <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 class="moz-txt-link-freetext" href="https://www.unavco.org/software/geodetic-utilities/geoid-height-calculator/geoid-height-calculator.html">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:part1.awror0LT.HCB8xP0j@gmail.com"></p>
    <div class="moz-cite-prefix">On 2023-01-03 12:54 a.m., Ujaval Gandhi
      wrote:<br>
    </div>
    <blockquote type="cite"
cite="mid:CALymcQBSu2xTL1d7qc8N=Ntj0ABzjddLD2N9P45RWWwjv5PRJw@mail.gmail.com">
      <meta http-equiv="content-type" content="text/html; charset=UTF-8">
      <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"
            moz-do-not-send="true" class="moz-txt-link-freetext">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"
              moz-do-not-send="true" class="moz-txt-link-freetext">qgis-user@lists.osgeo.org</a>>
            wrote:<br>
          </div>
          <blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
            <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:part2.dph5pyln.veauL60O@gmail.com"
                  alt="image.png" style="width: 844px; max-width: 100%;
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                  rgb(255, 255, 255) !important;" class=""><br>
                <br>
                <br>
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              <br>
              <img alt="" style="display: flex;"
src="https://mailtrack.io/trace/mail/72a173ca6bf77eea463768ff668b3c58b802c7ca.png?u=5552924"
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            <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"
                    moz-do-not-send="true" class="moz-txt-link-freetext">eddisonjose@gmail.com</a>>)
                  escribió:<br>
                </div>
                <blockquote class="gmail_quote" style="margin:0px 0px
                  0px
0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
                  <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:part3.sosTHCP6.fHBh6dUO@gmail.com"
                        alt="image.png" style="width: 334px; max-width:
                        100%; background-color: rgba(0, 0, 0, 0)
                        !important; border-color: rgb(255, 255, 255)
                        !important; color: rgb(255, 255, 255)
                        !important;" class=""><br>
                      <br>
                      <br>
                    </div>
                    <br>
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                    <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" moz-do-not-send="true"
                          class="moz-txt-link-freetext">njacadieux.gitlab@gmail.com</a>>)
                        escribió:<br>
                      </div>
                      <blockquote class="gmail_quote" style="margin:0px
                        0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
                        <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"
                                    moz-do-not-send="true"><span
                                      id="m_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"
                                    moz-do-not-send="true"
                                    class="moz-txt-link-freetext">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"
                                          moz-do-not-send="true"><span
                                            id="m_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;"
                                      moz-do-not-send="true" width="0"
                                      height="0"><img alt=""
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                                    <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"
                                          moz-do-not-send="true"
                                          class="moz-txt-link-freetext">njacadieux.gitlab@gmail.com</a>>)
                                        escribió:<br>
                                      </div>
                                      <blockquote class="gmail_quote"
                                        style="margin:0px 0px 0px
0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
                                        <div dir="auto">Hi,
                                          <div><br>
                                            <div>Google  vdatum <a
                                                href="https://vdatum.noaa.gov/"
                                                target="_blank"
                                                moz-do-not-send="true"><span
id="m_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"
                                                    moz-do-not-send="true"><span
id="m_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"
                                                    moz-do-not-send="true"
class="moz-txt-link-freetext">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;"
                                                      moz-do-not-send="true"
                                                      width="0"
                                                      height="0"></div>
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      -- <br>
      <div dir="ltr" class="gmail_signature"
        data-smartmail="gmail_signature">
        <div dir="ltr">---
          <div>Ujaval Gandhi</div>
          <div>Spatial Thoughts</div>
          <div><a href="http://www.spatialthoughts.com" target="_blank"
              moz-do-not-send="true">www.spatialthoughts.com</a></div>
          <div><br>
          </div>
        </div>
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    </blockquote>
    <pre class="moz-signature" cols="72">-- 
Nicolas Cadieux
<a class="moz-txt-link-freetext" href="https://gitlab.com/njacadieux">https://gitlab.com/njacadieux</a></pre>
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