[Proj] Coordinate within an area ?

Martin Raspaud martin.raspaud at smhi.se
Tue Mar 30 09:18:46 EST 2010

Hash: SHA1

Roger Oberholtzer skrev:
> On Tue, 2010-03-30 at 04:18 -0700, Hamish wrote:
>> Martin Raspaud wrote:
>>> Is there a way to know if a point defined by its lon/lat
>>> coordinates is within
>>> an area which corners are given in lon/lats also ?
>> yes, there are many methods to do this. try a web search
>> for "point in polygon". if it is corners of a box, it's trivial..
> As lat/longs and not meters? On a non-flat surface? Isn't it more
> complicated with lat/long for this? I would think you should convert the
> values to northings/eastings and do the test on that data. Then it could
> perhaps be a bounding box test.

Yes I thought about this, but wondered if there was a straight mthod I had missed.

> My next questions would be: (1) how accurate does it need to be? and (2)
> If it is done everywhere in the world, what projection to use to reduce
> error? I would think SMHI would be working in and near Sweden, and would
> be ok with SWEREF99.

1/ Not so accurate. We would have two areas, approximately the size of
scandinavia in different projections, and would want to know if there is
overlap. Missing an overlap to 5% is no big deal.
2/ We use global data, so it is everywhere in the world. I thought about using
Lambert azimuthal equal-area projection.

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