Cannot Find Polyline / Shape Trimming Solution?

I have the following polyshape, and I'm trying to get a code so that it'll be able to trim those little pieces outside the octagon, although I haven't been able to figure out if it's possible. The polyxpoly command also doesn't seem to be helpful.

It has the following data;

-0.469085968297298 0.313756744184688

-0.440094970502786 0.351396008350866

-0.407106781194909 0.470470623183810

-0.407106781194391 0.375735931293596

NaN NaN

-0.407106781192721 -0.449293596600183

-0.406889216222806 -0.478917063365948

-0.483600245002183 -0.299242467487661

-0.407106781189291 -0.375735931298804

NaN NaN

0.161453149357603 -0.944295861843129

0.175707373187741 -0.957130176681006

0.0289386891641220 -0.907106781194454

0.124264068706609 -0.907106781190604

NaN NaN

0.906666293448427 -0.907106781189538

0.954275060485152 -0.905749749128643

0.810953109152469 -0.971889603332103

0.875735931290109 -0.907106781190404

NaN NaN

1.46920860553500 -0.313634106950630

1.40640611899230 -0.462122697864436

1.40710678119355 -0.405794445824087

1.40710678119181 -0.375735931294404

NaN NaN

1.40710678119011 0.445567003765894

1.43208827956019 0.353126672561366

1.43836851515149 0.344474197336555

1.40710678118691 0.375735931300496

NaN NaN

0.817490374084150 0.965352338403833

0.930267025462621 0.905928057746692

0.913628423657978 0.907106781192067

0.875735931294209 0.907106781191396

NaN NaN

0.0554418305535038 0.907106781191186

0.0697100604909855 0.908422409793296

0.183050860302648 0.965893572774695

0.124264068708509 0.907106781191196

NaN NaN

1.40710678118691 0.375735931300496

1.40710678119181 -0.375735931294404

0.875735931290109 -0.907106781190404

0.124264068706609 -0.907106781190604

-0.407106781189291 -0.375735931298804

-0.407106781194391 0.375735931293596

0.124264068708509 0.907106781191196

0.875735931294209 0.907106781191396

Answer 1

[Jaynik]

Hi Owen,

To get a perfect octagon and trim off the unwanted edges, you might need to manually select the vertices that outline the desired octagon shape and then create a new "polyshape" with just those vertices.

To clean it programmatically, one approach that can be considered is to use convex hull. But this works only when the extra pieces are non-convex while the required octagon is supposed to be convex. Following is the sample code:

[k, v] = convhull(octagonData); % octagonData is the data provided above
convexPolyshape = polyshape(octagonData(k, :));
plot(convexPolyshape)

While this won't produce a perfect octagon, it will trim the unwanted edges and create a smoother outline. Note that you will need to delete the 'nan' values in order to execute the convhull function. You can refer the following documentation to read more about "convhull":

• https://www.mathworks.com/help/releases/R2021b/matlab/ref/convhull.html

Hope this helps!