Re: earthdistance

I also look at cube extension, but the built in type box - a couple of
points - does not require any extension and has a GIST index. It can be
used to represent a rectangle on the domain [-PI/2,+PI/2[*[-PI,PI[. If the
extension was providing a function get_rect_from_cap() giving the smallest
rectangle of this domain containing a spherical cap, this rectangle could
be used as you pointed out to reduce the set of rows where the earth
distance need to be computed to know if a point A belongs to the cap. The
operator && (box overlaps box) could be used if the point A is converted to
box(A,A). Do you think this function get_rect_from_cap() could be usefull?

2013/8/11 Bruno Wolff III <bruno(at)wolff(dot)to>

> On Sat, Aug 10, 2013 at 12:18:48 +0200,
> Olivier Chaussavoine <olivier(dot)chaussavoine(at)gmail(dot)**com<olivier(dot)chaussavoine(at)gmail(dot)com>>
> wrote:
>
>> I did not found any geographic indexing with earthdistance, and need it.
>>
>
> Some of the earthdistance stuff is based on cube which does have indexing.
> I don't know how well that indexing works and it might be pretty bad in
> practice.
>
>
> The need I have is simple:
>> "is the distance between two (lat,long) positions less than X km?"
>> the model used for the shape of the earth should be related to the
>> precision of lat,lon, and most sources are imprecise. The spherical model
>> should be enough.
>>
>
> You might just be looking at this wrong. You don't have an index on the
> distance. What you want is to find points within a cube that is big enough
> to include all of the points of interest and then double check the returned
> points to make sure they are really within the expected range. You can
> calculate the size of the cube needed based on the distance and the radius
> of the earth. I don't remember if there was a built in function for that,
> since it's been such a long time since I looked at it.
>

--
Olivier Chaussavoine