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    <div class="moz-cite-prefix">I was afraid that this was just me
      being stupid again.<br>
      Thanks so much for the explanation!<br>
      <br>
      <br>
      On 02/22/2013 07:57 PM, Martin Feuchtwanger wrote:<br>
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      <div class="moz-cite-prefix">Things behave as you'd expect going
        north/south because meridians of longitude are great circles
        (shortest paths on globe).<br>
        However, when you go east/west, parallels of latitude and great
        circles (shortest paths) are <b>not</b> the same. Parallels are
        convenient lines representing the graticule and represent <i>orthodromes</i>
        (lines of constant azimuth) but are not true great circles
        (which, presumably, st_project is following).<br>
        (FYI, if you were to follow an orthodrome in any other azimuth
        but the four cardinal directions, you'd spiral towards a pole!)<br>
        Spherical trigonometry's not always simple ;-)<br>
        <pre class="moz-signature" cols="72">Martin Feuchtwanger  <a moz-do-not-send="true" class="moz-txt-link-abbreviated" href="mailto:feumar@shaw.ca">feumar@shaw.ca</a>  604-254-0361
Vancouver, BC  V5N 1J6
<a moz-do-not-send="true" class="moz-txt-link-freetext" href="http://members.shaw.ca/geomatics.developer">http://members.shaw.ca/geomatics.developer</a>
</pre>
        On 21/02/2013 12:15 AM, News and Such wrote:<br>
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        <div class="post-text" itemprop="description"> Hello
          postgis'ers,<br>
          <br>
          somehow I can't understand the results of ST_Project, but
          maybe this problem is just me being stupid (again):<br>
          I just want to project a point in North, East, South and West
          direction.<br>
          <br>
          Note:<br>
          I use geography-type here, but the results are the same for
          geometry.<br>
          I use a rather long distance, because I need it, at least in
          one direction, for my application. Because of this I found the
          "problem" in the first place.<br>
          <br>
          With the direction north, everything is as I expect it:<br>
          <br>
          <code>SELECT ST_AsText(ST_Project('POINT(-30
            -0.5)'::geography, 1e7, radians(0))); <br>
            st_astext ----------------------------- <br>
            POINT(-30 89.4874128664049) </code><br>
          <br>
          But in the other directions, here for example East, I get
          this:<br>
          <br>
          <code>SELECT ST_AsText(ST_Project('POINT(-30
            -0.5)'::geography, 1e7, radians(90))); <br>
            st_astext --------------------------------------------- <br>
            POINT(59.8315233716443 0.00116689648502556) </code><br>
          <br>
          Shouldn't this be <code>POINT(59.8315233716443 -0.5)</code> ?
          Why are both coordinates changing?<br>
          <br>
          This behaviour occurs in all directions save north. <br>
          <br>
          I'm new to the whole earth coordinate system-stuff so maybe I
          missed something, but I thought that when one walks directly
          west (or south) one would, by definition, not leave the
          current longitude (or latitude)-line but only change the
          other.<br>
          <br>
          Any help would be appreciated! <br>
          Thank you.<br>
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</pre>
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