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nearestn.pro
nearestN takes takes a list of source locations and, for a list of test positions, returns the index of the n'th nearest source.
Routines
result = nearestn_findNeighbors(x, y, n, h, ri, nx, ny)findNeighbors is an internal routine used by nearestN.
result = nearestn(points, catalog, n [, dist=dist] [, all=all] [, verbose=verbose])This function returns the nth closest object to a given set of coordinates
Routine details
topnearestn_findNeighbors
result = nearestn_findNeighbors(x, y, n, h, ri, nx, ny)
findNeighbors is an internal routine used by nearestN. Given an (x,y) point and histogram information about a set of sample points, this function returns a list of at least n objects, one of which is guaranteed to be the nth nearest neighbor.
The function uses the reverse_indices variable from histogram to effeciently index objects nearby (x,y).
Return value
A list of indices referenceing objects in the histogram created in nearestN. One of these objects is guaranteed to be the nth nearest neighbor.
Parameters
- x in required
The x data point to find neighbors for
- y in required
The y data point to find neighbors for
- n in required
Ensure that the n'th nearest neighbor is included in the output
- h in required
The histgogram created in nearestN
- ri in required
The reverse indices variable from the histogram calculated in nearestN
- nx in required
The number of bins along the x axis in the histogram described by h
- ny in required
The number of bins along the y axis in the histogram described by h
topnearestn
catalog processing
result = nearestn(points, catalog, n [, dist=dist] [, all=all] [, verbose=verbose])
This function returns the nth closest object to a given set of coordinates
Designed to scale roughly linearly with the catalog size, as opposed to more common O(n^2) methods (e.g. computing every distance for each point and sorting).
Coordinate space is assumed to be euclidian.
Return value
A vector whose ith row gives the index of the nth closest point to points[i]
Parameters
- points in required
The points to find the nth nearest neighbor for
- catalog in required
A (2,m) array of m (x,y) points
- n in required
Find the n'th closest neighbor. The closest point corresponds to n = 0
Keywords
- dist in optional
A variable to hold the distances between the points and their nth nearest neighbors.
- all in optional
If set, returns all n+1 closest neightbor indices. In this case, the result is a n + 1 by m array
- verbose in optional
Print extra output
Author information
- History:
Written by: Chris Beaumont, September 2008 December 2008: Updated so that the points to find neighbors for need not be the list of object coordinates itself. cnb. March 2009: Added the DIST keyword. cnb. March 2009: Fixed bug when requesting n = 0. Added stricter input checking. cnb. March 2009: Added ALL keywrod. cnb. April 2009: Fixed bug in which test points outside the cloud of catalog points caused a crash. cnb. May 2009: Added VERBOSE keyword. cnb. June 2009: Reworked VERBOSE outputs to be used with VERBIAGE program. cnb. November 2009: Fixed bug that incorrectly populated the DIST array when /ALL was set
File attributes
| Modifcation date: | Mon Mar 22 16:17:13 2010 |
| Lines: | 211 |