I want to find the maximum distance between two points in a polygon made in MATLAB using roipoly. Then I want to find another line which is longest and which is perpendicular to the line joining points of maximum distance.
I was able to find the maximum distance points and make a line.(Figure attached) Now I want to find the maximum perpendicular distance to that line..
Any one who can help with MATLAB code for the same please revert back
Thanking you.
Regards
Hello Parth Shah,
I am sure there are many different ways to do that. I will give a short explanation how I would try it. I hope it will provide you a starting point.
First, try to not think of polygons as polygons when you work with them. A polygon is just a point set and you have all these points in a list, sort them, rearrange them, filter them, add new, remove some ... all that comfort we know from lists in C# or Java. You will be amazed how many new ideas you will get and how easy some stuff will be, as soon as you start thinking in sets not in shapes.
1) poly_1_BitmapFromPointlist.png
This is my starting point. I take your image and crop it, followed by a grayscale-conversion and a binarization. I extract all points from the binary mask again and put them into a list. Then I draw them back into a new image. But, this is basically your original image, I only removed the little squares and changed the colors.
2) poly_2MaxMinXY.png
First step, we determine the maximum dimension of all the points. For this, we need the lowest and highest x,y values occuring in the point set, regardless if it might be four different points. I do this by sorting the point list and then I grab the first and last elements. You can also iterate over all pixels, use some matlab function or whatever. Both max locations are now shown as blue circles in the image.
3) poly_3_BoundingRectangle.png
Just a little bit of cosmetics, using the identified maximum dimension we can draw a bounding rectangle. In this case especially nice because it provides us with a basic coordinate system. I think this might be useful later on.
4) poly_4_MaxPoints.png
In this step we draw the four corner points which were used in step 2 to determine the maximum dimension. But now we use the real points and they represent the border of our shape. Thanks to the basic coordinate system it is easier to identifiy all the basic geometric options, right triangles etc. and we know a lot of these points already.
5) poly_5_TriangleStart.png
Using the max-x and the max-y point we can obtain the points A, B and the hypotenuse c of the triangle we are looking for. We know we are looking for a right triangle and we now have: two points A and B, the hypotenuse c and the angles al and ga. Just in case you did not see it yet, follow the vertical line that you added to the image. Again we can keep it simple and just use another right triangle to obtain the angle al.
6) poly_6_Done.png
Well, mostly cosmetics in this step again. All angles and all sides were already known in the prior step. I use the angle al and the knowledge about the length of side b to draw the last point and complete the triangle. Well, there must be a some mistake I made because I still doubt that this a "real right angle", but maybe I am just sleepy.
I hope this will help you to find a starting point!
Good luck,
Robert
Can you share the code? Also I wanted the maximum perpendicular line which touches two ends of the polygon. Here it stops at the intersection. I want it to continue till the polygon boundary.
Thanks a lot Robert Fischer.
Hi Parth Shah,
I am implementing all my image processing stuff in .NET/C# and I am not sure if it would be helpful if I would just share this code. Thats why I tried to explain the basic steps without regards to a specific programming language. But feel free to ask if you have any questions of understanding.
With respect to your second question, have a look at the last image poly_6_Done.png please. There is another right triangle just on the opposite side of the blue triangle we already found. We already know two points and one side of the triangle. You can use this to do exactly the same what we did for the first triangle and obtain the point you are looking for.
I just used paint very quick to show the triangle.
Good luck!
Robert
This would be a classical optimization problem. The only subtlety is that your polygon is non-convex. Be prepared to use time consuming brute force methods. Perhaps, you would need to run through all the inside distances. A similar holds for finding the longest perpendicular from a vertex to this line.
From my knowledge and experience what ever Mr. Pavel Osinenko said is quite correct
- Badges
- Science topic