Steve, Oops I meant to say that I think PostGIS implements its own algorithm for distance. GEOS does have a distance calculation, and I'm actually kind of curious why that one is not used or maybe it was just more efficient speedwise to implement in PostGIS directly.
-----Original Message----- From: Obe, Regina Sent: Thursday, February 12, 2009 11:07 AM To: 'PostGIS Users Discussion' Subject: RE: [postgis-users] points from st_distance Well distance actually is not implemented in GEOS. PostGIS uses its own algorithm for that as I recall. -----Original Message----- From: postgis-users-boun...@postgis.refractions.net [mailto:postgis-users-boun...@postgis.refractions.net] On Behalf Of Stephen Woodbridge Sent: Thursday, February 12, 2009 10:54 AM To: PostGIS Users Discussion Subject: Re: [postgis-users] points from st_distance Ok, that would be cool. I could see a function like ST_ShortestLineBetween(geometry, geometry) that would return a line. You might want to write an enhancement bug for that. Since these things are implemented in GEOS, you might also want to add the request to the GEOS tracker too. -Steve. nicklas.a...@jordogskog.no wrote: > > Thanks a lot > > Regina is right about what I want to do and I agree that "any of the > points that satisfies the below > condition is a solution to that" > > I made some corresponding solution in avenue a few years ago but without > buffer. > > I don't think there is a practical problem, if you know about it, if you > just get one of possible many points at the same shortest distance. > If the geometries is not snapped to a grid there should be very few > cases when more than one point from each geometry represents the > shortest line between the geometries if the precision of the > calculations is good enough. > I still think it would be great with a built in function. I think it > ought to be much more efficient to get the points at the same time as > finding the closest distance instead of throwing them away inside the > function and then finding them again outside the function. > > This is not an acute problem for me right now but I can see a lot of > possibilites from such a function. It would be possible to easy build > snapfunctions. It would also increase the possibilites to analyze what's > between two geometries. > > If we could get the shortest line between geometries just as effective > as we now get the shortest distance I think it would open many doors. > Back in avenue this problem blocked the creative developing thinking > many times. But that's just from my quite amateur point of view. > > thanks again > Nicklas > > 2009-02-11 Paragon Corporation wrote: > > Steve, > > > >Maybe I misunderstood his question. I thought what he was asking was > > > >1) since ST_Distance gives the distance between the 2 points of each > >geometry that are closest. What is that point(s) that it is using. > > > >So our thinking is is that any of the points that satisfies the below > >condition is a solution to that > > > >So say you have Geometry A and geometry B and you want to know what set of > >points on Geometry A are closest to Geometry B > > > >The answer would be > > > >SELECT ST_Intersection(A, ST_Buffer(B, ST_Distance(A,B))) > > > >Hope that helps, > >Regina > > > >-----Original Message----- > >From: postgis-users-boun...@postgis.refractions.net > >[mailto:postgis-users-boun...@postgis.refractions.net] On Behalf Of > Stephen > >Woodbridge > >Sent: Wednesday, February 11, 2009 11:50 AM > >To: PostGIS Users Discussion > >Subject: Re: [postgis-users] points from st_distance > > > >Hmmmm, why not do something like: > > > > > >select *, ST_distance(point, object) as dist from table expand(point, > >min_distance) && object and dist <= min_distance order by dist limit 1; > > > >-Steve > > > > > >Paragon Corporation wrote: > >> > >> Nicklas, > >> > >> You are correct there is no function for doing this. We have on > >> occasion needed to do this ourselves and what we usually do is > >> > >> 1) first find the minimum distance > >> 2) figure out which point/pointset on the geometry satisfies the > >> minimum distance using buffer and intersection (with minimum distance > >> being the buffer distance). > >> > >> I think I have the code lying around here somewhere. > >> > >> As far as ST_Distance goes. Haven't looked at the code that closely, > >> but it does some sort of recursive call and there could be more than > >> one point that satisfies the condition and it only cares about the > >> first one it comes across so such a thing may or may not be quite what > >> you are looking for. > >> > >> Hope that helps, > >> Regina > >> > >> > >> > >> *From:* postgis-users-boun...@postgis.refractions.net > >> [mailto:postgis-users-boun...@postgis.refractions.net] *On Behalf Of > >> *nicklas.a...@jordogskog.no > >> *Sent:* Wednesday, February 11, 2009 4:47 AM > >> *To:* postgis-users@postgis.refractions.net > >> *Subject:* [postgis-users] points from st_distance > >> > >> Hallo > >> > >> I have a question or suggestion. > >> > >> If I have missed some functionality please tell me. > >> > >> The thing is I have often needed information about from which points > >> the distance in st_distance is calculated. > >> I mean, somewhere in the function the information have to be. Would it > >> be possible to build a new function which returned the distance, > >> startpoint, endpoint as array or something like that. > >> > >> Am I right about that this functionality is missing and am I right > >> about that the points have to be identified somewhere in the function > >> and that it ought to be possible to present them in a function. > >> > >> If I'm right so far I would like to come this as a suggestion. > >> > >> I also have to thank you all for postgis. > >> It has been a very nice experience to start handling the gis analysing > >> and processing in database-environment. > >> My next step is to try to manage any of the procedural languages. Then > >> I guess I can do just anything with all the points and polygons out > there > >:-). > >> > >> /Nicklas > >> > >> > >> ---------------------------------------------------------------------- > >> -- > >> > >> _______________________________________________ > >> postgis-users mailing list > >> postgis-users@postgis.refractions.net > >> http://postgis.refractions.net/mailman/listinfo/postgis-users > > > >_______________________________________________ > >postgis-users mailing list > >postgis-users@postgis.refractions.net > >http://postgis.refractions.net/mailman/listinfo/postgis-users > > > > > >__________ Information from ESET NOD32 Antivirus, version of virus > signature > >database 3842 (20090210) __________ > > > >The message was checked by ESET NOD32 Antivirus. > > > >http://www.eset.com > > > > > > > > > >_______________________________________________ > >postgis-users mailing list > >postgis-users@postgis.refractions.net > >http://postgis.refractions.net/mailman/listinfo/postgis-users > > > > > > > ------------------------------------------------------------------------ > > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users ----------------------------------------- The substance of this message, including any attachments, may be confidential, legally privileged and/or exempt from disclosure pursuant to Massachusetts law. 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