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 <br...@wolff.to> > On Sat, Aug 10, 2013 at 12:18:48 +0200, > Olivier Chaussavoine > <olivier.chaussavoine@gmail.**com<olivier.chaussavo...@gmail.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
