How to extract the data using inpolygon function ?

Hi everyone,

May some one help me here ...

I have data in three colums. (1) x-coordinate; (2) y-coordinate; and (3) z-value (parametere) of data length (55000 data points: I reduce the file size due to limit of 5 MB) I required to extarct the z-values lying inside the polygon.

My scripit did not work for the above mentioned purpose. May someone help me how to handle this data and simple script attched here.

clear all
clc
 data=xlsread('Mc_catalog.xlsx');
 for i=1:length(data)
 x = data(:,1) ; y = data(:,2) ; z = data(:,3 ) ;
xVertices = [-116.8, -116.7, -116.45, -116.7];
yVertices = [33.55, 33.40, 33.70, 33.85];
idx(i) = inpolygon(x(i), y(i), xVertices, yVertices);
iwant(i) = [ z(idx )] ;
 end

Thank you.

Answer 1

[Cris LaPierre]

Consult the inpolygon documentation page. You can probably do this without the for loop, as inpolygon can query a vector of points at once.

Here is an example from the linked page.

% Define polygon
L = linspace(0,2*pi,6);
xv = cos(L)';
yv = sin(L)';

% Define points to query
xq = randn(250,1);
yq = randn(250,1);

% Find points inside polygon
[in,on] = inpolygon(xq,yq,xv,yv);

% Visualize results
figure

plot(xv,yv) % polygon
axis equal

hold on
plot(xq(in),yq(in),'r+') % points inside
plot(xq(~in),yq(~in),'bo') % points outside
hold off

[aa]

I even try with out the for loop but the output show empty iwant(see my code).

Yes, I follow this exmaple but this not serve for my purpose may you modify

clear all
clc
 data=xlsread('Mc_catalog.xlsx');
 x = data(:,1) ; y = data(:,2) ; z = data(:,3 ) ;
xVertices = [-116.8, -116.7, -116.45, -116.7];
yVertices = [33.55, 33.40, 33.70, 33.85];
idx = inpolygon(x, y, xVertices, yVertices);
iwant = [ z(idx )] ;

[Cris LaPierre]

This syntax should work. Perhaps data does not have the values you think it does?

Here's how I might visualize the results.

data = readmatrix('data_new.xlsx');

x = data(:,1) ; y = data(:,2) ; z = data(:,3 ) ;
xVertices = [-116.8, -116.7, -116.45, -116.7];
yVertices = [33.55, 33.40, 33.70, 33.85];

idx = inpolygon(x, y, xVertices, yVertices);
iwant = z(idx);

% Visualize
plot3(xVertices,yVertices,zeros(size(xVertices)))
hold on
scatter3(x(idx),y(idx),iwant)
hold off

[aa]

Thank you very much this serve for my purpose.