[postgis-users] selection of data in WGS84 lat/lon over the noth pole

[Brian Modra]

2009/9/28 Brian Modra <brian at zwartberg.com>:
> 2009/9/28 Malm Paul <paul.malm at saabgroup.com>:
>> Hi list,
>> I would like to select data over the north pole inside a polygon of lat/lon coordinates
>> For selection I create a polygon from theese coordinates
>>
>> 1) 80, -170
>> 2) 80, 170
>> 3) 75, 10
>> 4) 75, -10
>>
>> But is seems that the objects found are from around the pole instead of over the pole, it does not find any objects over 80°
>> Is ther a way to get around this?
>
> This is a wild guess, having not looked at the PostGIS code, and not
> knowing how your data is stored, but I wonder if you need to put in
> more coords, because depending on the prjection, the lines joining
> those 4 points could be kind of weird.
>
> e.g.
> 80 0, 80 20, 80 40, 80 50, 80 60... 80 180, 80 -160, 80 -140 ... 80 0

Another question for the experts:
what is the inside of the polygon in the above example? Is it above
80, or below 80, or is the polygon joined up as a straight line at 80
degrees? I.e. with zero area?

maybe a better polygon would be:

80 -170, 80 -150, 80 -130 ... 80 150, 80 170, 75 170, 75 150, 75 130
... 75 -150, 75 -170, 80 -170

>
>> Kind regards,
>> Paul
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>
>
>
> --
> Brian Modra   Land line: +27 23 5411 462
> Mobile: +27 79 69 77 082
> 5 Jan Louw Str, Prince Albert, 6930
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>



-- 
Brian Modra   Land line: +27 23 5411 462
Mobile: +27 79 69 77 082
5 Jan Louw Str, Prince Albert, 6930
Postal: P.O. Box 2, Prince Albert 6930
South Africa
http://www.zwartberg.com/