inpolygon command for multiple areas

Hi all,

In part of my code I am intrested in realizing whether a point = (x,y) is withing multiple areas or not. Here, each area is a polygon (simply a square) that have the coordination of its center locater which I can calcuate the corner points.

I learnt that by using "inpolygon" comman I can realize whether my point is withing that polygon(or on its edge). Hoever, I am interested to recognize what area whose the point is withing.

i.e. I have area1, area2 and area3.

I set following variables:

% definig all the areas coordination
xv = [1 2 2 1 1 NaN 4 4 5 5 4 NaN 6 6 7 7 6]; 

yv = [0 0 3 3 0 NaN 1 2 2 1 1 NaN 4 5 5 4 4];

x = 1.5;

y = 3;

in = inpolygon(x,y,xv,yv);

I can find that my point is within one of the three defined areas (Here is within the area1). But how can I say the point is within what area specifically?

I would appreciate if get some help in this,

Best

Answer 1

[Kelly Kearney]

This should do it:

http://www.mathworks.com/matlabcentral/fileexchange/7187-inpolygons

Note that that function expects polygons to be defined with clockwise vertices (counterclockwise is reserved for holes), so you'd have to preprocess your vertices:

xv = [1 2 2 1 1 NaN 4 4 5 5 4 NaN 6 6 7 7 6];
yv = [0 0 3 3 0 NaN 1 2 2 1 1 NaN 4 5 5 4 4];

x = 1.5;
y = 3;

[xv, yv] = poly2cw(xv, yv);

[in, idx] = inpolygons(x, y, xv, yv]

[tafteh]

Thanks Kelly.

[tafteh]

Hi Kelly,

I learnt that I do not have "Mapping Toolbox". Hence I can not run your code. Any other solution?!

[Kelly Kearney]

Sorry, I always forget that the polygon tools (ispolycw, poly2cw, polybool, etc) are Mapping Toolbox functions. They really ought to move those to the base toolbox; I would think geometric calculations like that would be useful for non-mapping purposes.

Anyway, in answer to your question, inpolygons is basically just a glorified loop over the inpolygon function. I included specific restrictions on orientation so it could be used with shapefile-derived polygons, but for your purposes, this probably isn't necessary. You can probably modify my code accordingly; just break your initial vectors based on the NaNs, then loop over each polygon with inpolygon.

[tafteh]

Modified your code and its working!

Thanks again for your help:)