[OpenLayers-Users] Square miles from Square degrees?

[Linda Rawson]

I have had a few issues with the Mercator functions.  I had to use
parseFloat on the values I passed into it.

Linda Rawson

On Dec 17, 2007 11:31 AM, cmose <cjmose at gmail.com> wrote:

>
> Hmnn after giving this a go I seem to be getting wildly inaccurate
> results,
> at least I believe I am. For instance, I used a polygon over an area I
> know
> to be roughly 400k square kilometers. Using the getArea on the polygon
> (after converting points to sphericalmercator) I'm getting a result of
> 748,912,714 sq. km...
>
> Anyone have any pointers or ideas of where I might be going wrong here?
> Thanks!
>
> Josh Livni-4 wrote:
> >
> >
> > I've not played with the getArea function, but since area calculations
> > in the base coordinate system (geographic/dec. degrees, or however it's
> > best described) make no sense, I think the only way you can do this with
> > the current codebase would be to use the forwardMercator equations found
> > in OpenLayers.Layer.SphericalMercator.
> >
> > After reprojecting your geometry to spherical-mercator, an area
> > calculation would make more sense, and be in meters (though still be off
> > by I'm guessing a few percent, depending on the size of your geometry
> > and it's location).
> >
> > I think the trunk and next version of OL may include additional methods
> > of getting to use SphericalMercator, and perhaps even other projections,
> > but I'm not too clued in on the details.
> >
> > -Josh
> >
> >
> > cmose wrote:
> >> Hopefully I'm not making a fool of myself but my assumption is that the
> >> getArea function on Geometry/subclasses returns square degrees (that
> >> seems
> >> to be the case to my eye). How exactly would I go about calculating
> >> square
> >> miles from this or is that even possible? If not, how do I go about
> >> calculating the square miles contained in a shape drawn on the map?
> >>
> >> Thanks!
> >>
> > _______________________________________________
> > Users mailing list
> > Users at openlayers.org
> > http://openlayers.org/mailman/listinfo/users
> >
> >
>
> --
> View this message in context:
> http://www.nabble.com/Square-miles-from-Square-degrees--tp14357316p14373973.html
> Sent from the OpenLayers Users mailing list archive at Nabble.com<http://nabble.com/>
> .
>
> _______________________________________________
>  Users mailing list
> Users at openlayers.org
> http://openlayers.org/mailman/listinfo/users
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.osgeo.org/pipermail/openlayers-users/attachments/20071217/ce828034/attachment.html