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<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D;mso-fareast-language:EN-US">There is over 25,000 m elevation difference on Mars so yes, it may well be important there.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D;mso-fareast-language:EN-US">Altitude above sea level or some other datum requires a reference geoid. Center of the planet would seem naively at least not to, though perhaps even that is less simple
than one might hope. <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Barkley, Erik J (3970) <Erik.J.Barkley@jpl.nasa.gov>
<br>
<b>Sent:</b> 06 October 2018 03:28<br>
<b>To:</b> Colin.Haddow@esa.int; Anthony Crowson <anthony.crowson@telespazio-vega.de><br>
<b>Cc:</b> Bui, Tung (397G) <Tung.Bui@jpl.nasa.gov>; CCSDS Service Mgmt WG <smwg@mailman.ccsds.org><br>
<b>Subject:</b> PIF question -- off earth aperture coordinates<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif">Colin, Anthony,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif">As you may recall, the PIF has an accommodation for specifying the coordinates for apertures on celestial bodies other than earth. You may also recall that we (NASA/JPL)
are supporting one of the prototypes for the PIF exchange. In working through this, we have found out that indeed the Mars relative Lat/Long coordinates are used for determining the communication geometry for the overflight orbiters. But the PIF appears to
be a tad bit deficient in that it only specifies Lat/Long whereas the current local implementation used in coordinating all of this also supplies altitude as part of the coordinate information. Given that Mars definitely has variations in local terrain altitude,
I think this is in fact important to include in the PIF. In fact in poking around with the internal services I made a query that returned location information indicating over 3,300 m in elevation -- I suspect that if we are to be accurate etc. this has some
bearing on the communication geometry in terms of properly reporting range and/or light time. However, somewhat interesting to me is that the altitude is from the center of the planet. It seems a bit odd but it also makes sense in that there really is no
definition of “sea level” for Mars. So my suggestion is to add an altitude parameter as indicated below. Perhaps we can further discuss this at the Berlin meetings.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif">Best regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif">-Erik
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><img width="731" height="723" style="width:7.6145in;height:7.5312in" id="Picture_x0020_1" src="cid:image001.jpg@01D45EED.BDFAB010" alt="cid:image001.jpg@01D45EED.BDFAB010"><span lang="EN-US" style="font-size:12.0pt;font-family:"Georgia",serif"><o:p></o:p></span></p>
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