[Mapserver-users] Question about projections conversions...

Wed Feb 11 14:37:16 PST 2004

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  Hi all,
  In my application I needed to calculate a area. My points were in
WGS84. So, I did some projection conversions from WGS84 to utm WGS84 so
that I could calculate my area in meters or any other metric unit.
  Everything went fine, until I compared my area results with the same
area results from MapInfo. The mapscript area was with a 0,3% error. In
small areas this is nothing, but for medium to big areas, which is my
case, this error is quite big.
  I talked to the guy who did the MapInfo calculations to get the area.
He said that this error probably is because I'm using utm, which doesn't
considers the earth flattening or something like that.
  So I wanted to ask you this: Is there a way to calculate the area
using mapscript and proj.4 that considers the earth flattening or
something like that (I really don't know the term for that).
  Thanks in advance,
     Murilo

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<p class=3DMsoNormal><font size=3D2 face=3DArial><span lang=3DEN-US =
style=3D'font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-US'><span
style=3D'mso-spacerun:yes'>  </span>Hi =
all,<o:p></o:p></span></font></p>

In my application I needed to =
calculate a area. My points were in WGS84. So, I did some =
projection conversions
from WGS84 to utm WGS84 so that I could =
calculate my
area in meters or any other metric unit.<o:p></o:p>

Everything went fine, until I =
compared
my area results with the same area results from MapInfo. The mapscript area was with a 0,3%
error. In small areas this is nothing, but for medium to big areas, =
which is my
case, this error is quite big…<o:p></o:p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span lang=3DEN-US =
style=3D'font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-US'><span
style=3D'mso-spacerun:yes'>  </span>I talked to the guy who did the =
MapInfo calculations
to get the area… He said that this error probably is because =
I’m
using <span class=3DSpellE>utm</span>, which doesn’t considers the =
earth
flattening or something like that.<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span lang=3DEN-US =
style=3D'font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-US'><span
style=3D'mso-spacerun:yes'>  </span>So I wanted to ask you this: Is =
there a
way to calculate the area using <span class=3DSpellE>mapscript</span> =
and proj.4
that considers the earth flattening or something like that (I really =
don’t
know the term for that).<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span lang=3DEN-US =
style=3D'font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-US'><span
style=3D'mso-spacerun:yes'>  </span>Thanks in =
advance,<o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 face=3DArial><span lang=3DEN-US =
style=3D'font-size:
10.0pt;font-family:Arial;mso-ansi-language:EN-US'><span
style=3D'mso-spacerun:yes'>     =
</span>Murilo<o:p></o:p></span></font></p>

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