Check this out:
http://www.movable-type.co.uk/scripts/latlong-vincenty.html
Should be easy to port the code.
If you do this, can you report out on your experience? E.g. does this
run fast, does it give you the results you're looking for, etc.
Jeff Adams wrote:
Wow, what a conversation I started!
So here's my use case:
I have a web app that is displaying polygons and points (different
layers) on a "North America" scale (although of course you can zoom in
to any particular area of interest). All the data is in "Web
Mercator" projection.
1) I need to allow the user to choose a location and "search by radius
(in miles)" for features in one of the point or polygon layers.
2) I need to find the nearest polygon to a point (although this one is
less critical, as it's a hack to get around bad data and there's a
chance we can get better data).
Any reprojecting I will be doing will be on the fly, as the underlying
data has to remain in web mercator. Since we're talking a web app,
I'm a little concerned about reprojecting a whole lot of polygons on
the fly just to check distance, I'm concerned that performance will be
a problem (I.E. it won't be very responsive). Some of the polygons
follow county boundaries and stuff so they can have a lot of points
(although I could simplify them first if it were faster).
Paul, I would love to get your code for "Vicinity Distance". In the
interests of full disclosure however I must admit this is paid work
for a commercial customer, so I can understand if you do not wish to
give me a copy of the code.
Thanks,
Jeff
On Thu, Feb 5, 2009 at 1:08 PM, Martin Davis <[email protected]
<mailto:[email protected]>> wrote:
Another issue with ellipsoidal (geodetic) calculation is the whole
date line/poles wrapping issue. This is a major pain to deal
with. I guess local projections can be used to deal with this as
well, though.
Seems like it would be nice to have a library that would
automatically choose the best projection, do the transformation,
compute the result, and untransform...
--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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