Creating grid with incremental numbers around specific coordinate

Hi

I'm trying to solve a problem on cody that involves creating a function (safety_map(N, R, C)) for the creation of a grid of safety levels around a specific coordinate.

As an example, if the input is safety_map(5, 2, 3), the result should be the following:

[3 2 2 2 3;
3 2 1 2 3;
3 2 2 2 3;
3 3 3 3 3;
4 4 4 4 4]

I started with something like this:

gr = zeros(N)
for i = 1:(N-1)
    r1 = R - i
    r2 = R + i
    c1 = C - i
    c2 = C + i

For a simpler matrix or if 1 is at the center of the matrix I can write some code. But when eventually r1 or c1 <= 0 and r2 or c2 > N I strugle bad. The only way I see it is to write every condition possible...

Does anyone have some ideas on how to write a smaller function?

Thanks

Answer 1

[Walter Roberson]

N = 5; r = 2; c = 3;
temp = true(N,N);
gr = bwdistgeodesic(temp, c, r) + 1

gr = 5×5

3 2 2 2 3 3 2 1 2 3 3 2 2 2 3 3 3 3 3 3 4 4 4 4 4

[Luís Duarte]

Thanks!

But I don't have Image Processing tool box, and to submit my answer on cody I would need a solution that doesn't need addons

[Walter Roberson]

for i = 1:(N-1)
    r1 = R - i

You are trying to define the coordinates for a box that you are going to write into. But one or more edges of the box might be outside the array. Consider that this has two effects:

1. This might imply that you should not draw the edge
2. The edges drawn in the perpendicular direction need to stop at the boundary

You only have a small number of cases to deal with.

• if this edge would be outside the matrix for its row/column, then do not draw it at all
• otherwise, you can use max() and min() to determine the drawing limits