| Re: help with data points of contour. [message #16904] |
Wed, 25 August 1999 00:00 |
Nando Iavarone
Messages: 48
Registered: December 1998
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Member |
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<HTML>
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> z(i,j)=sqrt(x(i)^2+y(j)^2)
<BR> endfor
<BR> endfor
<BR>contour,z,x,y,levels=[10,20,30,40]
<BR>end</BLOCKQUOTE>
a question.why do you use loop?
<BR> I use the technique:
<P>pro test
<P> nn=101
<P> x = findgen(nn)-(nn-1.)/2.
<BR> y = x
<BR> x = x#replicate(1,nn)
<BR> y = replicate(1,nn)#y
<P> z = sqrt(x^2+y^2)
<BR>
<BR>end
<P>don't you think it is more readeble and maybe, I didn't test it, quicker?
<BR>
<BLOCKQUOTE TYPE=CITE>I now want to determine the x,y data points that
form the z=20 contour.</BLOCKQUOTE>
I think that if you are interested only in discrete value of your coordinate,it
is sufficient to do:
<P>index = where(z eq 20)
<BR>x_index = index mod nn
<BR>y_index = index / nn
<BR>print, x_index, y_index
<P>bye.
<PRE>--
Nando Iavarone
Advanced Computer System - SPACE DIVISION
via Lazzaro Belli, 23
00040 Frascati - RM
Tel: +39-6-944091 (switchboard)
9440968 (direct)
E-mail:
f.iavarone@acsys.it
FrdndVrn@altavista.net</PRE>
</HTML>
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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  |
Ben Tupper
Messages: 186
Registered: August 1999
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Senior Member |
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<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
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> z(i,j)=sqrt(x(i)^2+y(j)^2)
<br> endfor
<br> 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>
<p>Something like this...
<p>pro test
<br>
<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> z(i,j)=sqrt(x(i)^2+y(j)^2)
<br> endfor
<br> endfor
<br>
<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> ;it should apears like this
<br>;IDL> help,path_info[1],/struct
<br>;** Structure CONTOUR_PATH_STRUCTURE, 6 tags, length=16:
<br>; TYPE &n bsp;
BYTE &n bsp; 1
<br>; HIGH_LOW &a mp;nbsp; BYTE &n bsp;
0
<br>; LEVEL & nbsp;
INT &nb sp; &nb sp;
3
<br>; N   ;   ;
LONG &n bsp; &n bsp;
308
<br>; OFFSET & ;nbsp;
LONG &n bsp; &n bsp;
5
<br>; VALUE & nbsp;
FLOAT & nbsp; 40.0000
<p>Offset = Path_Info[1].Offset ; start at index Offset
<br>N = Path_Info[1].N &n bsp; &n bsp;
; there are N verticies
<p> ; 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;
FLOAT = Array[2, 308]
<br>
<p>stop
<br>end
<br>
<pre>--
Ben Tupper
Bigelow Laboratory for Ocean Science
tupper@seadas.bigelow.org
Pemaquid River Company
pemaquidriver@tidewater.net</pre>
</html>
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