Code for telling if coordinate is outside, inside or on the border of shape

Question

User types value of x and y which will be a coordinate. There is some kind of a shape there and I need to tell if that coordinate will be outside, inside or on the border of that shape. I know how to do that with rectangle shape, but not with triangle or circle. Currently I need to do this with this shape: http://i.imgur.com/5teZk85.png

How do I do this for circle or triangle shape?

For rectangle I used these code lines:

IF (x>=-5) AND (x<=2) AND (y>=-1) AND (y<=3) then
   IF (x=-5) OR (x=2) OR (y=-1) OR (y=3) then
      writeln('Dot is located on line')
   else writeln('Dot is located inside')
   else writeln('Dot is located outside');

To get answer from SO, you would need to provide some more details on how do you model the problem in your program using your chosen programming language. — George Polevoy, Sep 16 '14 at 15:00
It's a wide topic. check this pdf: http://www.cs.princeton.edu/courses/archive/fall05/cos226/lectures/geosearch.pdf — Spindizzy, Sep 16 '14 at 18:24

score 3 · Accepted Answer · edited May 23 '17 at 12:29

3

For a circle, you can do the following test:

If x^2 + y^2 < r^2, then it is inside the circle.

For triangles, you should probably look at this question: How to determine if a point is in a 2D triangle?

edited May 23 '17 at 12:29

Community

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answered Sep 16 '14 at 15:03

Reed Oei

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And how can i tell if it's going to be on the border of circle and not inside/outside? – rits Sep 16 '14 at 16:42
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If it is on the border of the circle, `x^2 + y^2 = r^2`, and if it is outside, then `x^2 + y^2 > r^2`. – Reed Oei Sep 16 '14 at 18:33

Spindizzy · Answer 2 · 2014-09-16T18:23:59.617

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A while ago I enrolled for an online course about algorithms, held by Robert Sedgewick. One topic was "Geometric Search", it describes you problem. Therefore I don't want to post a code snippet here, but suggest to read one of his books. See my comment for a pdf that might help you to get on the right track.

edited Sep 16 '14 at 18:23

answered Sep 16 '14 at 15:24

Spindizzy

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A link to an external site that provides the solution is not considered an answer here. You should either provide an answer here post the link as a comment to the original question instead. – Ken White Sep 16 '14 at 16:55

Code for telling if coordinate is outside, inside or on the border of shape

2 Answers2