Make a mask and apply it to other matlab figures

Hi everyone,

I have an ensamble of point and for each of them a value (x,y,value). I need to make a contour plot whit this data. I resolved the problem in two different ways: (1) the scatter function and (2) the delaunayTriangulation with trisurf functions. These two figures are the results. These pictures represent a flow over a cylinder. The problem is that I'd like to use the second solution in order to have a better contour, but I need the cylinder zone also. The trisurf function works with an interpolation that make contour appears also in the cylinder zone. I need a solution that I can apply also to more complex geometry. Make a mask by selecting points from the figure is not very user-friendly. Someone can help me?

Answer 1

[Hornett]

To exclude a specific zone like a cylinder from your contour plot while using trisurf in MATLAB, follow these steps:

1. Define the Exclusion Zone: Determine the mathematical representation of your exclusion zone (e.g., for a cylinder, use its center coordinates and radius).
2. Filter Out Points Within the Exclusion Zone: For each point in your dataset, check if it falls within the exclusion zone (e.g., for a cylinder, check if a point is within the cylinder's radius). Exclude these points from your dataset

% Assuming cx, cy, r represent the cylinder's center and radius

insideCylinderIdx = (x - cx).^2 + (y - cy).^2 <= r^2;

xFiltered = x(~insideCylinderIdx);

yFiltered = y(~insideCylinderIdx);

valuesFiltered = values(~insideCylinderIdx);

3.Perform Delaunay Triangulation on Filtered Data: Use the filtered dataset (points outside the exclusion zone) to perform Delaunay triangulation.

tri = delaunay(xFiltered, yFiltered);

4. Plot Using trisurf: Use the trisurf function to create a surface plot from the triangulated data.

trisurf(tri, xFiltered, yFiltered, valuesFiltered);

This approach allows you to create contour plots that exclude specific zones, such as a cylinder, and can be adapted to more complex geometries by appropriately defining and filtering out the exclusion zones before triangulation and plotting.

You can reffer to following documention for more details : https://www.mathworks.com/help/matlab/ref/trisurf.html

I hope it helps