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<p class=MsoNormal>Good evening,<o:p></o:p></p>
<p class=MsoNormal> I’m a total postGIS newbie and I’ve done some
searching but I haven’t found an answer yet.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal> I’ve found and tried using the st_distance_spheroid
function, and that seems to return a result as I would expect. However, I have
a project where my goal is to determine what points fall within ¼ mile of a
point that a user would specify as well as determining the elevation difference
to the selected points from the user specified point.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal> I’ve defined my geometry field with the Z value that
we’ve pre-calculated, and that seems to show up properly when looking at
the values using the st_AsEWKT function.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal> I was initially thinking I would have to generate a line
object for the two points in question using ST_Makeline, use that distance with
the st_length3d_spheroid function to compare with the 2d distance returned by st_distance_spheroid
and calculate for the other side of the triangle to get the elevation
difference, but that doesn’t seem to match the elevation numbers I have.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal> I did have to transform everything into latlong to get the
distance functions to work…but I have a feeling that I’m over
thinking this. There should be some kind of function to return the Z value
difference between two geometries right? <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal> Could someone please point me in that direction?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Thanks,<o:p></o:p></p>
<p class=MsoNormal>Matthew<o:p></o:p></p>
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