Hi Apurv, Thanks for that - I understand better now.
I guess by multidimensional scaling you mean any heuristic that would give a "good enough" solution with some indication of goodness of fit, e.g. classic MDS but also simulated annealing etc. I don't think either GeoTools, or the JTS library which it uses for geometry operations, have what you want, though I'd be happy to be corrected by someone else here. In the plane I **think** that the coordinate that minimizes the sum of distances to all points in a set is the median, ie. centroid.x = median of point.xs, centroid.y = median of point.ys. If your points are often close together (local or regional scales) you could just work with Cartesian coordinates in some convenient map projection. However, you emphasize spheroidal distance in your post so I'm guessing that your point sets cover a large area. In that case I've no idea whether there is an easy solution, but once again it depends on how critical the minimum sum of distances criterion is for your application. GeoTools does have the GeodeticCalculator class which can compute distances between points on a spheroid. So you could use that in conjunction with an optimizing algorithm from another library. As an aside, why are you searching in GeoTools for this ? I would have thought the first stop would have been R (which has many packages for spatial analysis) or similar. Sorry I can't be more directly helpful but please let us know how you go. Michael On 25 July 2011 19:32, Apurv Verma <[email protected]> wrote: > Hi Michael, > I am extremely sorry that I did not cc my message to the list last time. > Thanks for providing me with the link. > > Well let me tell me you my problem in detail. > From the pdf I found that the minimum distance centroid would be the closest > that I would want. How can I compute it. However it would be better if > something of the following is provided. > I have a set of points on the surface of earth. I want to calculate a > central point such that the distance from it to the given points is in > required proportion with the additional requirement that this point should > be inside the polygon obtained by joining the points. > It's easy to see that a such a requirement cannot be perfectly met. Let me > give you an analogy in the euclidean geometry rather than spherical > geometry. > Suppose I have 4 points in the Euclidean plane. I want to calculate a point > which is equidistant/distances in equal proportions to the 4 points. Now > this is not always possible because if I choose a circle to pass through 3 > points, it's not necessary that the fourth point too lies on the circle. > (because 3 points uniquely define a circle.) > So then we can do a kind of multidimensional scaling. Such that we try to > find a point which satisfies the criterion as best as it can. > While this is challenging enough to calculate on a euclidean plane. > Spherical geometry makes things even worse!! > > I hope I was able to explain myself. Please do ask me if I was not clear. > > -- > thanks and regards, > > ~Apurv Verma > B. Tech.(CSE) > IIT- Ropar > Mobile - 09256587545 > > > > > > > On Mon, Jul 25, 2011 at 1:10 PM, Michael Bedward <[email protected]> > wrote: >> >> Hello, >> >> Please reply via the list. >> >> So what sort of centroid do you want ? There are many in common use >> (see http://user.gs.rmit.edu.au/rod/files/publications/MSIA_Centroid.pdf >> for a comparison of some). >> >> Or is it enough to have any point that is inside some polygon formed >> by the data points e.g. the convex hull ? >> >> Michael >> >> >> On 25 July 2011 16:58, Apurv Verma <[email protected]> wrote: >> > Yes it is a type of centroid calculation only. >> > Given a polygon on the surface of earth, I need to calculate its >> > centroid. >> > Have a look at this page. >> > http://www.fmepedia.com/index.php/InsidePointReplacer >> > >> > thanks and regards, >> > >> > ~Apurv Verma >> > B. Tech.(CSE) >> > IIT- Ropar >> > Mobile - 09256587545 >> > >> > >> > >> > >> > >> > >> > On Mon, Jul 25, 2011 at 10:37 AM, Michael Bedward >> > <[email protected]> wrote: >> >> >> >> Hello Apurv, >> >> >> >> > I am absolutely new to the geo tool library. In fact I want to use >> >> > it >> >> > for a >> >> > specific purpose in the open source project "phyloGeoRef". >> >> >> >> Great to see taxonomy / biogeography making an appearance here :) >> >> >> >> > Here is the >> >> > functionality that I want. >> >> >> >> > Given a set of (lat,long) pairs on the globe. I have to calculate the >> >> > inside >> >> > point replacer for these set of nodes. Is there some function in Geo >> >> > Tools >> >> > that provides this functionality. If not, Is there any other method >> >> > to >> >> > do it >> >> > ? >> >> >> >> Can you provide more detail about the required output. I'm not >> >> familiar with the term "inside point replacer" and Wikipedia doesn't >> >> seem to know it either. Is it a type of centroid calculation ? >> >> >> >> Michael >> > >> > > > ------------------------------------------------------------------------------ Storage Efficiency Calculator This modeling tool is based on patent-pending intellectual property that has been used successfully in hundreds of IBM storage optimization engage- ments, worldwide. Store less, Store more with what you own, Move data to the right place. Try It Now! http://www.accelacomm.com/jaw/sfnl/114/51427378/ _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
