| Re: tracing contours, how? [message #10798 is a reply to message #10730] |
Fri, 23 January 1998 00:00   |
Armand J. L. Jongen
Messages: 9
Registered: April 1997
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Junior Member |
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Thorsten Becker wrote:
>
> Hi,
>
> I am trying to trace a special contour line in a 2D field, t, to
> get the coordinates in data units. I tried
>
> CONTOUR, t, PATH_XY=xy, PATH_INFO=info, levels=contourlevels
> k = 0
> FOR i=0, (N_ELEMENTS(info) - 1 ) DO BEGIN
> FOR j=0, info(i).n-1 DO BEGIN
> IF((info(i).value EQ tracecontourvalue)THEN BEGIN
> print, info(i).value, xy(0, k+j), xy(1, k+j)
> ENDIF
> ENDFOR
> k = j
> ENDFOR
>
> and was hoping that this would trace the polygons and give me all points
> in normalized units if the contourvalue is tracecontourlevel. I got the
> right contour, but the points it printed didn't really make sense. Why?
> Did anybody solve this problem with IDL? Your help is greatly appreciated.
I think that for just getting the coordinates for one polygon at a
certain level the suggestion from David works best. So just do:
CONTOUR, t, PATH_XY=xy, /Path_Data_Coords, $
levels=tracecontourvalue
Both probably you have some troubles that there are more polygons at the
same level generated and you want to seperate them. The way I did this
for selscting the longest polygon is:
; Here I set the desired thresholdvalue
Levels=[ThresHoldVal]
Contour, ImageData, /Follow, $
Levels=Levels, /Closed, $
Path_XY=xy, Path_Info=pathinfo, /Path_Data_Coords
; Check if there are results and then
If N_Elements(pathinfo) GT 0 Then Begin
; choose a selection-criterion
; I look for the longest polygon
Dum = Max(pathinfo.N,IMax)
; Look at the manual pages for Contour. The returned Path_XY is NOT
; in device_coords but also needs a offset
S = [INDGEN(pathinfo(IMax).N), 0]
; Here the area xy(*, pathinfo(IMax).Offset+S) contains the polygon
coords in
; /device for the selected polygon.
PlotS, xy(*, pathinfo(IMax).Offset+S), /Device
Endif
I hope this helps. Remember to look at the manual page for Contour to
see how Path_XY and Path_Info are returned.
Cheers,
--
************************************************************ ************
Armand J.L. Jongen Academic Medical Centre
Laser Centre
Phone +31-20-5667418 \\||||// Meibergdreef 9
Fax +31-20-6975594 | ~ ~ | 1105 AZ Amsterdam
E-mail a.j.jongen@amc.uva.nl [| o o |] The Netherlands
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