<HTML><BODY style="word-wrap: break-word; -khtml-nbsp-mode: space; -khtml-line-break: after-white-space; ">Thanks for everyone's help. <DIV><BR class="khtml-block-placeholder"></DIV><DIV>Aimee Mostella</DIV><DIV><BR><DIV><DIV>On Jul 20, 2005, at 1:58 PM, William Thompson wrote:</DIV><BR class="Apple-interchange-newline"><BLOCKQUOTE type="cite"><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Aimee:</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">You may be interested in these frame definition files I put together for the STEREO project.<SPAN class="Apple-converted-space"> </SPAN>The file heliospheric.tf is generic, and can be used for any mission.<SPAN class="Apple-converted-space"> </SPAN>The stereo_rtn.tf is an implementation of the HGRTN coordinate system specific to the two STEREO spacecraft--you can use it as a template for your own mission.</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><A href="http://sohowww.nascom.nasa.gov/solarsoft/stereo/gen/data/spice/gen/heliospheric.tf">http://sohowww.nascom.nasa.gov/solarsoft/stereo/gen/data/spice/gen/heliospheric.tf</A></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><A href="http://sohowww.nascom.nasa.gov/solarsoft/stereo/gen/data/spice/gen/stereo_rtn.tf">http://sohowww.nascom.nasa.gov/solarsoft/stereo/gen/data/spice/gen/stereo_rtn.tf</A></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Bill Thompson</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Aimee Mostella wrote:</DIV> <BR><BLOCKQUOTE type="cite"><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Hello, I'm using spkezr to get the position of a spacecraft (target) in the J2000 reference frame with the observer as the Sun.<SPAN class="Apple-converted-space"> </SPAN>What coordinate system is this based upon?<SPAN class="Apple-converted-space"> </SPAN>Is it Heliocentric Aries Ecliptic HAEJ2000?<SPAN class="Apple-converted-space"> </SPAN>Ultimately, I need to get the lat and lon of the spacecraft based on the Heliocentric of Date (HCD) coordinate system so that I can convert to Heliocentric RTN (HGRTN).<SPAN class="Apple-converted-space"> </SPAN>I thought I could either get the position of the spacecraft in HAEJ2000 and convert to HCD from there or get the position in GEIJ2000 and convert from there.<SPAN class="Apple-converted-space"> </SPAN>However, when I tried the GEIJ2000 route, my calculations were more off than they were when I did it from scratch.<SPAN class="Apple-converted-space"> </SPAN>I tried the algorithm in the SPK Required Reading but still didn't get a good answer.<SPAN class="Apple-converted-space"> </SPAN>Any suggestions?<SPAN class="Apple-converted-space"> </SPAN>Thanks</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">~~~~~~~~~~~~~~~~~~~~~~~</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Aimee Mostella Research Analyst</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Southwest Research Institute</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Space Science Division</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">(210) 522-6735</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">------------------------------------------------------------------------</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">_______________________________________________</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Spice_discussion mailing list</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><A href="mailto:Spice_discussion@naif.jpl.nasa.gov">Spice_discussion@naif.jpl.nasa.gov</A></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><A href="http://naif.jpl.nasa.gov/mailman/listinfo/spice_discussion">http://naif.jpl.nasa.gov/mailman/listinfo/spice_discussion</A></DIV> <BR></BLOCKQUOTE><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">--<SPAN class="Apple-converted-space"> </SPAN></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">William Thompson</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">NASA Goddard Space Flight Center</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Code 612.1</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">Greenbelt, MD<SPAN class="Apple-converted-space"> </SPAN>20771</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">USA</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; min-height: 14px; "><BR></DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; ">301-286-2040</DIV><DIV style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; "><A href="mailto:William.T.Thompson.1@gsfc.nasa.gov">William.T.Thompson.1@gsfc.nasa.gov</A></DIV> <BR class="Apple-interchange-newline"></BLOCKQUOTE></DIV><BR><DIV> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px"><BR></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">~~~~~~~~~~~~~~~~~~~~~~~</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Aimee Mostella<SPAN class="Apple-converted-space"> </SPAN></FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Research Analyst</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Southwest Research Institute</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">Space Science Division</FONT></P> <P style="margin: 0.0px 0.0px 0.0px 0.0px"><FONT face="Helvetica" size="3" style="font: 12.0px Helvetica">(210) 522-6735</FONT></P> </DIV><BR></DIV></BODY></HTML>