How can I get X, Y (and Z) coordinates of a shape (/Body) in Matlab?

Hi I have a rectangle with rounded corners which I got through this:

figure
rectangle('position',[0 -1 10 2],'Curvature',[1])
axis equal
grid minor

But I need to get a list of x,y coordinates starting at the middle of the bottom line. it would also be useful to vary the number of coordinates I can get.

I'm trying to get draw a plate (basically a rectangle with rounded corners). If I don't use the function I did before how could I do it? essentially the x-coordinates would be the length of the plate, and the y-coordinates would be the height. I'm trying to get a number of x,y coordinates (which I can vary, say 200 coordinates to start with) starting at the middle bottom of the plate and then going anti-clockwise around the plate.

So to recap, starting at the middle bottom of the plate i need to get around 200 x,y coordinates anti-clockwise back to the middle bottom of the plate, but these coordinates have to follow a specific geometry (for now the shape of the plate, I think later I might change the shape.

[So i need a continuous path of points, equal distance from each other, following the perimeter of a shape/drawing/line/etc.]

I'm finding it really hard to explain, I hope this helps at least a little.

Regards,

[Adam Danz]

1. draw two horizontal parallel lines at a distanc of 'd'
2. draw to 1/2 circles with diameter 'd' centered at the end of each line, between the two lines.

[Cam S]

What does this do to help me?

[Adam Danz]

"I'm trying to get draw a plate (basically a rectangle with rounded corners). If I don't use the function I did before how could I do it? "

What I understand from this is that you want to recreate the image produced by the rectangle function you shared and to get the coordinates at a fixed interval.

One way to do that is by using linspace() to draw two horizontal parallel lines (step 1 in my comment above) and then to draw two half circles at each end (my step 2).

It's not a complete solution which is why my comment is not in the 'answers' section. But it's a push in the right direction.

[Cam S]

Oh I see. I forgot I asked that part. What I am really trying to do is trace the perimeter of any shape with points. And then find the coordinates of those points.

Any ideas?

[Adam Danz]

Are the shapes always formed by a black line on a white background?

Are the shapes always stored in a matlab figure? jpg?

[Cam S]

Generally yes. White on black. And the shape can be made anywhere, photoshop, illustrator,etc. as a png or jpeg. Then in matlab, points are assigned to the black lines.

[Adam Danz]

I would start my converting the image to binary using imbinarize()

https://www.mathworks.com/help/images/ref/imbinarize.html

Then you can get the coordinates of the black lines by

[y, x] = find(bw);
% or
[y, x] = find(~bw);

[Cam S]

Ok, and what if I want each recorded point to be say... 8 pixels from each other. So I have 500 points that show the same thing instead of an infinite amount or like 10000000?

[Adam Danz]

Once you get the (x,y) coordinates from my suggestion above (or from another method), you can interpolate the coordinates using interp1()

https://www.mathworks.com/help/matlab/ref/interp1.html

[Cam S]

Is that like taking a small sample of the data?

[Adam Danz]

No, interpolation means that you are generating a new set of coordinates defined by the current coordinates. For example,

x = [1,2,3,4,5];
y = [.1 .2 .3 .4 .5];

% interpolated to 1/2 of the interval
x1 = [1 1.5 2 2.5 3 3.5 4 4.5 5]; 
y1 = [.1 .15 .2 .25 .3 .35 .4 .45 .5];

[Cam S]

Ohh, that’s neat. The documentation is a bit confusing. Could you explain how to use the functions. I appreciate all this help btw. ;)

[Adam Danz]

Yeah, it can be confusing for newbies. I find it helpful to followi the examples that are included in all matlab functions in the documentation. For example, here's the example section for interp1

https://www.mathworks.com/help/matlab/ref/interp1.html#btwp6lt-5

[Cam S]

Cool. Thanks.