How can I find the index of a point in an array?

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Agustin 2017-7-11

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评论： Star Strider 2017-7-12

Hi! I have the following point: tmp = [-119.3 1042.5] and I want the index of this point in a grid. I have two separate grids, xdata and ydata and I'm trying to find the indexes, ipix and jpix. When I'm looking for ipix using

ipix = find(xdata == tmp(1,1))

I get the following:

ipix =
   Empty matrix: 0-by-1

The numbers on the xdata and ydata grids are the form -1.193846913204592e+02 and when I write

ipix = find(xdata == -1.193846913204592e+02)

I get

ipix =
         71361

which makes no sense. Can somebody help me with this? What I need is to find the index of the given point so I can find the displacement of the point in different images.

Thank you;

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采纳的回答

Star Strider 2017-7-11

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This is due to floating-point approximation error. You have to search within a range of tolerances.

Try something like this:

tol = 0.001;
[xrow,xcol] = find((xdata >= tmp(1,1)-tol) & (xdata <= tmp(1,1)+tol)); 
[yrow,ycol] = find((xdata >= tmp(1,2)-tol) & (xdata <= tmp(1,2)+tol));

For a more extended discussion, see Why is 0.3 - 0.2 - 0.1 (or similar) not equal to zero? (link)