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Re: help with data points of contour. [message #16915 is a reply to message #16904] Tue, 24 August 1999 00:00 Go to previous message
Ben Tupper is currently offline  Ben Tupper
Messages: 186
Registered: August 1999
Senior Member
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Peter Brooker wrote:
<blockquote TYPE=CITE>Consider the following simple program.
<p>nn=101
<br>x=findgen(nn)-(nn-1.)/2.
<br>y=x
<br>z=fltarr(nn,nn)
<br>for i=0,(nn-1) do begin
<br>for j=0,(nn-1) do begin
<br>&nbsp;&nbsp; z(i,j)=sqrt(x(i)^2+y(j)^2)
<br>&nbsp;&nbsp; endfor
<br>&nbsp;&nbsp; endfor
<br>contour,z,x,y,levels=[10,20,30,40]
<br>end
<p>I now want to determine the x,y data points that form the z=20 contour.
<br>How do I do this. The manual is rather cryptic on this.
<p>thanks-Peter Brooker</blockquote>
The contour positions can be written to a variable using the PATH_INFO
and PATH_XY.
<br>&nbsp;
<p>Something like this...
<p>pro test
<br>&nbsp;
<p>nn=101
<br>x=findgen(nn)-(nn-1.)/2.
<br>y=x
<br>z=fltarr(nn,nn)
<p>for i=0,(nn-1) do begin
<br>for j=0,(nn-1) do begin
<br>&nbsp;&nbsp; z(i,j)=sqrt(x(i)^2+y(j)^2)
<br>&nbsp;&nbsp; endfor
<br>&nbsp;&nbsp; endfor
<br>&nbsp;
<p>contour,z,x,y,levels=[10,20,30,40],Path_XY = Path_XY,Path_Info = Path_Info
<p>; the Path_info contains such as number of verticies and how far down
the list in Path_XY they start
<br>; level 20 is index #1 in this case
<p>help, Path_Info[1], /struct
<p>&nbsp;;it should apears like this
<br>;IDL> help,path_info[1],/struct
<br>;** Structure CONTOUR_PATH_STRUCTURE, 6 tags, length=16:
<br>;&nbsp;&nbsp; TYPE&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
BYTE&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp; 1
<br>;&nbsp; HIGH_LOW&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&a mp;nbsp;&nbsp; BYTE&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;
0
<br>;&nbsp;&nbsp; LEVEL&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;& nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
INT&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb sp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb sp;&nbsp;
3
<br>;&nbsp;&nbsp; N&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp ;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp ;&nbsp;&nbsp;
LONG&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;
308
<br>;&nbsp; OFFSET&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;& ;nbsp;&nbsp;&nbsp;&nbsp;
LONG&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;&nbsp;&nbsp;
5
<br>;&nbsp; VALUE&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;& nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
FLOAT&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;& nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 40.0000
<p>Offset = Path_Info[1].Offset&nbsp;&nbsp;&nbsp; ; start at index Offset
<br>N = Path_Info[1].N&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n bsp;&nbsp;&nbsp;&nbsp;&nbsp;
; there are N verticies
<p>&nbsp;; to get the XY pairings of the verticies
<p>XY20 = Path_XY[*,Offset:Offset+N-1]
<p>help, XY20
<p>;IDL> help,XY20
<br> ;XY20&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;& nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
FLOAT&nbsp;&nbsp;&nbsp;&nbsp; = Array[2, 308]
<br>&nbsp;
<p>stop
<br>end
<br>&nbsp;
<pre>--&nbsp;
Ben Tupper

Bigelow Laboratory for Ocean Science
tupper@seadas.bigelow.org

Pemaquid River Company
pemaquidriver@tidewater.net</pre>
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