> I have a bunch of blobs. (Think spots on the
> Gateway cow.) I would like to analyze the curvature
> and bends in the perimeter of the blobs. I have
> the indices of the points that make up the blob, and
> I have obtained the "perimeter" points by contouring
> the blob. Unfortunately, these perimeter points are
> not evenly distributed. (Think of a blob that has a
> long, straight side. The contour command will put a
> point at either end of the straight bit, so the points
> on that side of the blob are sparse, while the points
> along a tight bend on the other side of the blob
> are dense.)
Hi,
I have stumbled over this ground before. I use the FillIn_Contour
function pasted in below. It's pretty typical of my brute force
technique for doing geometery with IDL.
While we are on the subject of contouring, I recall that a call to
CONTOUR with the Path_XY keyword set to retrieve the vertex pairs will
change the direct graphics plot scaling. A call to CONTOUR with the
OverPlot keyword set does not change the plot scaling. I *always*
forget that Contour does this when someone signing my paycheck is
looking over my shoulder. I show an example of this in the
FunnyContour procedure below.
Ben
;*******START EXAMPLE HERE
PRO FunnyContour
TVLCT, R, G, B, /get
Img = BytArr(100,100)
Img[25:75,25:75] = 1
Img = Rot(Img, 30)
Img[0:50, *] = 0
LoadCT, 0, bottom = 32
Tek_Color
ImDisp, Img, /no_Scale, /Axis, /Erase
Print, 'XS after plot ', !X.S
;save these for later
XS = !X.S
YS = !Y.S
;contour directly to the display - shown in red
Contour, Img, levels = [1], c_color = 2, /over
Print, 'XS after contour to display ', !X.S
;contour directly to the output keywords show in green
Contour, Img, levels = [1], Path_XY = xy, /Path_Data_Coord
Print, 'XS after contour to path_xy ', !X.S
oPlot, XY[0,*], XY[1,*], color = 3, psym = 1
;restore the plotting parameters
;and show the results in blue
!X.S = XS
!Y.S = YS
oPlot, XY[0,*], XY[1,*], color = 4, psym = 2
;pad in the missing pixel locations
;show these in orange
newXY = FillIn_Contour(XY)
oPlot, newXY[0,*], newXY[1,*], color = 8, psym = 5
TVLCT, R, G, B
END
;*******END EXAMPLE HERE
;**********ANOTHER START HERE
;+
; NAME:
; FillIn_CONTOUR
;
; PURPOSE:
; Given the XY data path coordinates returned
; from a call to CONTOUR using
; an image, this routine returns ALL of the pixels
; coordinates that lie along the contour.
;
; CATEGORY:
; Image analysis.
;
; ARGUMENTS:
; XY A 2xn element array of contour vertices returned
; by the CONTOUR routine keyword PATH_XY.
; DELTA A one or two element vector of the 'pixel'
; size in the x and y directions. By default [1,1] is used.
;
; RETURNED:
; A 2xm element array of the coordinates of all
; the pixels/cells that lie along the path.
; The first point and last are the not the same.
;
; EXAMPLE:
; ;make an image
; img = BytArr(250,250)
; Img[50:200, 50:200] = 1
; Tek_color
; TV, Image
; CONTOUR, img, Path_XY = XY,
; /Path_Data_Coord, Levels = [1]
; ;only 4 vertices (since the 'island' is a rectangle
; plots, XY[0,*], XY[1,*], psym = 6, color = 2, /dev
; ;get all the pixels
; newxy = filin_contour(xy)
; ;show the new points
; plots,newXY[0,*], newXY[1,*], psym = 3, /dev, color = 3
;
; MODIFICATION HISTORY
; 18 JUNE 2001 Written by Ben Tupper.
;-
FUNCTION FillIn_Contour, XY, delta
;establish the step size
Case n_elements(Delta) of
0: d = [1.0,1.0]
1: d = [float(delta),delta]
Else: d = Float(Delta[0:1])
EndCase
d = ABS(d)
neg_d = 0.0 - d
;convert original array into 'wrapped' vectors
oX = [Reform(XY[0,*]), XY[0,0]]
oY = [Reform(XY[1,*]), XY[1,0]]
;seed the new xy paring
X = Ptr_new(oX[0])
Y = Ptr_New(oY[0])
;step through the original verticies, padding the
;'new' vertices as needed
i = 1L & newCount = 1L
While i lt n_elements(oX) do begin
;get the x and y displacements
dx = oX[i] - (*X)[newCount-1]
dy = oY[i] - (*Y)[newCount-1]
Case 1 of
;in this case the next vertex in origianl set
is more than
;one pixel away
ABS(dx) GT d[0] OR ABS(dy) GT d[1]: Begin
*X = [*X,(*X)[newCount-1] + (neg_d[0] > dx < d[0])]
*Y = [*Y,(*Y)[newCount-1] + (neg_d[1] > dy < d[1])]
;the newCount will be incremented, but
not the
;counter for the old set
newCount = NewCount+1
End ;big gap to be filled in
;in this case we have arrived at a vertex... so simply
;move on to the next vertex in the original data set
dx EQ 0 AND dy EQ 0: i = i+1
;in this case the next vertex is the one form the
original data set
Else: Begin
*X = [*X, oX[i]]
*Y = [*Y, oY[i]]
;move on to the next vertex
i = i + 1
NewCount = NewCount + 1
End
EndCase
EndWhile
NewXY = $
transpose( [ [ (*X)[0: newCount-2] ],[ (*Y)[0: newCount-2] ]
])
ptr_free, X,Y
Return, NewXY
END
;*********ANOTHER END HERE
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
