defining a polygon area within an array

I have a 2D array of numbers.

I have a polygon with defined x and y coordinates.

Could someone please help me set the area within the array that the polygon overlaps to 0 please.

Answer 1

[Akira Agata]

How about the following solution?

% 100-by-100 sample matrix
Zin = peaks(100);
Zin = Zin - min(Zin(:));

% Example of polygon
pgon = polyshape([10 10 80 30], [10 30 30 10]);

% Create logical index which indicates inside/outsize the polygon
[colGrid,rowGrid] = meshgrid(1:size(Zin,2),1:size(Zin,1));
idx = isinterior(pgon,[colGrid(:),rowGrid(:)]);
idx = reshape(idx,size(Zin));

% Set elements inside the polygon to 0
Zout = Zin;
Zout(idx) = 0;

% Show the result
figure
subplot(2,2,1)
contourf(Zin)
title('Original','FontSize',14)
colorbar
subplot(2,2,2)
plot(pgon)
xlim([1 100])
ylim([1 100])
box on
title('Polygon','FontSize',14)
subplot(2,2,3)
contourf(Zout)
title('Result','FontSize',18)
colorbar

Answer 2

[Walter Roberson]

If you have the Computer Vision Toolbox, then you can use https://www.mathworks.com/help/vision/ref/insertshape.html#btppvxj-1-shape insertShape with 'filledpolygon' and 'Color', 'k' . This will write 0s into the part of the rectangle indicated by the coordinates. The resulting array will have been converted to RGB, but you can just take the first pane of it.

[Jonathan]

Hi there is valuable information in the resulting array containing numbers that are essential for analysis. Is there anyway of using a function (maybe without the computer vision toolbox) that can preserve the resulting array?