| tracing contours, how? [message #10730] |
Thu, 22 January 1998 00:00  |
becker
Messages: 1
Registered: January 1998
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Junior Member |
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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.
Thanks in advance
Thorsten
Thorsten W. Becker________________________becker@fas.harvard.edu
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| 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
*****************************o00o***(__)***o00o************* ************
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| Re: tracing contours, how? [message #10829 is a reply to message #10730] |
Thu, 22 January 1998 00:00 |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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Thorsten Becker (becker@fas.harvard.edu) writes:
> 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?
Perhaps I don't understand this question, but why won't
this work:
CONTOUR, t, PATH_XY=xy, /Path_Data_Coords, $
levels=tracecontourvalue
Cheers,
David
-----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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