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Function poly2cw not working?

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Xiaohan Du
Xiaohan Du il 12 Nov 2017
Risposto: Veda Upadhye il 15 Nov 2017
Hi all,
Matlab says:
[x2, y2] = poly2cw(x1, y1) arranges the vertices in the polygonal contour (x1, y1) in clockwise order, returning the result in x2 and y2.
However, if I have the (x1, y1) coordinates as:
x1 =
-1 -1 0 0
y1 =
-1 0 -1 0
obviously the poly2cw result should be:
>> x2
x2 =
-1 -1 0 0
>> y2
y2 =
-1 0 0 -1
However, if I run
>> [x2 y2] = poly2cw(x1, y1)
x2 =
-1 -1 0 0
y2 =
-1 0 -1 0
The result is not clockwise? Why?
Or
>> [x3 y3] = poly2ccw(x1, y1)
x3 =
0 0 -1 -1
y3 =
0 -1 0 -1
It's not counterclockwise either.

Risposte (1)

Veda Upadhye
Veda Upadhye il 15 Nov 2017
Hi,
This is actually the expected behavior of the "poly2cw" function. This function expects its input to be a counter clockwise ordered polygon and simply reorders the vertices bottom to top to change the ordering to clockwise.
If you wish to plot points in the clockwise direction, I would suggest using the "convhull" function before the "poly2cw" function. The "convhull" function converts the unordered set of points to counter-clockwise ordered points. You may then use the "poly2cw" to convert them to clockwise order. Here is an example demonstrating this:
K = convhull(x1,y1);
ccx = x1(K);
ccy = y1(K);
[cx,cy] = poly2cw(ccx,ccy);
Documentation for the "convhull" function can be found here:
Hope this helps!
-Veda

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