| Re: Edge detection and convert edges into polygons [message #61899] |
Mon, 04 August 2008 00:50  |
M. Suklitsch
Messages: 12
Registered: August 2008
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Junior Member |
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Hi!
Thanks for the quick replies!
Paolo, I have several subregions, defined over a specific area. These
subregions are sometimes bigger (> 100 pixels), sometimes only consist
of three or four pixels. And yes, I want to find out in which of these
subregions my station, or more general a point of interest, lies.
David, this is what I've come up with thanks to your hints. Although
this code works, maybe there is some shortcut that makes the whole
thing even better?
FOR mm = 1, iNumOfRegs-1 DO BEGIN
; do some edge detection in rgiGridMsk
rgiIndices = WHERE(rgiGridMsk EQ mm)
IF rgiIndices[0] NE -1 THEN BEGIN
rgiBoundary = Find_Boundary(rgiIndices,$
xsize=rgiGridSiz[0],ysize=rgiGridSiz[1])
rgrXVect = FLTARR(N_ELEMENTS(rgiBoundary)/2) & rgrYVect =
rgrXVect
; now get the corresponding lat/lon values and store them as
vectors
FOR nn = 0, N_ELEMENTS(rgiBoundary)/2 -1 DO BEGIN
rgrXVect[nn] =
rgrGridLon[rgiBoundary[0,nn],rgiBoundary[1,nn]]
rgrYVect[nn] =
rgrGridLat[rgiBoundary[0,nn],rgiBoundary[1,nn]]
ENDFOR
; put the polygons into IDLanROI object
grROI = OBJ_NEW('IDLanROI', rgrXVect, rgrYVect)
; use IDLanROI->ContainsPoints to check whether stations lie
; within or without a region
rgiMatch = grROI->ContainsPoints(rgrLon,rgrLat)
iFoundMatch = (WHERE(rgiMatch NE 0))[0]
IF iFoundMatch NE -1 THEN BEGIN
rgiStationMaskIdx[WHERE(rgiMatch NE 0)] = mm
ENDIF
ENDIF
ENDFOR
Maybe a short explanation: rgrLon and rgrLat are vectors holding the
longitude and latitude of several points of interest,
rgiStationMaskIdx is a vector of the same size as rgrLon where the
corresponding subregion index is stored.
Cheers,
Martin
David Fanning schrieb:
>
> I think I would just work with the integer mask and find
> the boundaries around the sub-regions:
>
> http://www.dfanning.com/ip_tips/boundary.html
>
> You can use the boundary directly to create an IDLanROI
> object, or (probably a good idea) you can reduce the
> number of vertices in the boundary with MESH_DECIMATE
> first.
>
> Cheers,
>
> David
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
> Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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