Thanks a million chris I had in mind a more suitable place for other questions of this type, i.e. general gis questions rather than special postgis questions
Anyway, your kind help was so useful for me Best Regards. ________________________________ From: Chris Hermansen <[email protected]> To: PostGIS Users Discussion <[email protected]> Sent: Thu, June 23, 2011 10:10:29 AM Subject: Re: [postgis-users] Interpolation problem Hi Saka; AFAIK any transmitter that can be modelled as a point source in 3D should be inverse square, it's just electromagnetic radiation after all :-) If you have enough points in your grid of known (x, y, p1, p2, p3) then you can do a least squares fit on all of the parameters. Of course if your transmitters move around, you are stuck. Again, a poor r-squared / big residuals would indicate errors. Also, if your transmitters are relatively far away from the grid but close to each other, I would think you would start to get an ill-conditioned system. I don't mind continuing the discussion by e-mail if you like. Certainly our colleagues on this list are probably not so interested in the problem. chris dot hermansen at tecogroup dot ca On Wed, Jun 22, 2011 at 10:26 PM, Saka Royban <[email protected]> wrote: Thanks a lot Chris. >some points: >1. Are u sure that all transmitters of this type use inverse square law? >2. If we don't know position of transmitters, can we still solve the problem >in >least square? maybe using dD=Di-Dj paramater or so. >3. I think we can suppose all transmitters to be from the same mark, so the >fixed constant in formula. > >(this subject sounds a bit off topic, regarding postgis. Do u know any better >place (i.e mailing list or so) for this kind of discussions?) > >Best Regards >Saka > > > > > ________________________________ From: Chris Hermansen <[email protected]> >To: PostGIS Users Discussion <[email protected]> >Sent: Wed, June 22, 2011 9:39:36 AM > >Subject: Re: [postgis-users] Interpolation problem > > > >Oh wait. Maybe each transmitter occupies a separate xy location so you are >then >able to calculate distance from each transmitter using an inverse square law >and >finally solve for the unknown xy location? >If so you should be able to first determine your constants Ki i = 1,2,3 for >each transmitter in >Si = Ki / (Di * Di) >by doing a least squares fit on the known signal strengths vs known distances >(calculated from known xy). >If the fit doesn't provide small residuals / high correlation then you will >probably have a hard time with your subsequent computations... >On 2011-06-21 9:57 PM, "Chris Hermansen" <[email protected]> wrote: >> Would not there be isolines of the same signal strength? In that case there >> is no unique x,y for a given signal strength... >> On 2011-06-21 9:54 PM, "Saka Royban" <[email protected]> wrote: >>> yes, of course.there is a unique x,y for each triple measurements. >>> This measurements are, in fact, Received Signal Strength so it means more >>> distance less RSS value. >>> >>> >>> >>> >>> >>> ________________________________ >>> From: Chris Hermansen <[email protected]> >>> To: PostGIS Users Discussion <[email protected]> >>> Sent: Wed, June 22, 2011 8:35:05 AM >>> Subject: Re: [postgis-users] Interpolation problem >>> >>> >>> What are the three measurements? Is it reasonable to assume that knowing >> three >>> measurement values tells you the location ie is there a unique x,y for >> each >>> triple of measurements? >>> On 2011-06-21 8:54 PM, "Saka Royban" <[email protected]> wrote: >>>> Hi all >>>> I'm not sure whether this can be done completely via PostGIS or it needs >> some >>>> programming. Anyway, at this step no problem with programming if Knowing >> the >>>>way >>>> >>>> >>>> and algorithm. >>>> I have point shapefile (arranged like a grid) and for each point there is >> 3 >>>> similar measurements (obtained via 3 transmitters) and, of course, x and >> y >>>> coordinates. The problem is that when i have a new point with these 3 >> measures, >>>> >>>> How can i interpolate its coordinates and specify its location? >>>> Maybe helpful to say, this type of measurement is distance dependent but >>>> unfortunately i don't know the exact formula. >>>> >>>> Any help would be appreciated. >>>> Best Regards > >_______________________________________________ >postgis-users mailing list >[email protected] >http://postgis.refractions.net/mailman/listinfo/postgis-users > > -- Chris Hermansen Vice President TECO Natural Resource Group Limited 301 · 958 West 8th Avenue Vancouver BC CANADA · V5Z 1E5 Tel +1.604.714.2878 · Cel +1.778.840.4625
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