polyind.m

基于matlab的反演程序,用于地球物理勘探中射线追踪及偏移成像程序.

function [jmin,jmax] = polyind(ipoly,x,y)

% [jmin,jmax] = polyind(ipoly,x,y)
%
% x,y	= input arrays of polygon coordinates
% ipoly = input desired index of polygon is 
% 
% POLYIND returns:
% jmin 	= index of the first point
% jmax 	= index of the last point
%   
% Tom Bishop, Oct.93
%
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% Project sponsor. By using this software, you are agreeing to the terms
% detailed in this software's Matlab source file.
 
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%
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% of Geology and Geophysics of the University of Calgary, Calgary,
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% compute distmax
distmax=.05;    %threshold of 5 percent of picture
scalex=1./(max(x)-min(x));
scaley=1./(max(y)-min(y));
j=0;
distnext=distmax;
%
%loop thru all polygons
%
for loop = 1:ipoly
  jmin = j+1;  %reset from last polygon
  dist = distmax + 1;   % dont want 2nd point 
  j=jmin+1;
  while (dist > distmax) | (dist >= distnext) 
    j=j+1;
    if(j > length(x))
%      fprintf('reached end of array, length = %d\n',length(x))
      jmax = length(x);
      return
    end
    distx = scalex*(x(j)-x(jmin));
    disty = scaley*(y(j)-y(jmin));
    dist  = sqrt(distx.^2 + disty.^2);
    jnext = min(j+1,length(x));  %dont run off end of array
    distxnext = scalex*(x(jnext)-x(jmin));
    distynext = scaley*(y(jnext)-y(jmin));
    distnext  = sqrt(distxnext.^2 + distynext.^2);
%    fprintf('dist,distnext,j =  %8.4f %8.4f %d\n',...
%             dist,distnext,j) 
  end
  jmax=j;
end