Re: Calculating distance using hex coordinate system

Torben, that did the trick! Thank you very much for your assistance!

On Mon, 17 Sep 2007 12:15:24 +0200, torbenm@xxxxxxxxxxxxx (Torben
Ægidius Mogensen) wrote:

me@xxxxxxxxxxx writes:

Howdy all,

I've created a hex grid bitmap, and have assigned each hex a
coordinate exactly as portrayed on this page, and am now
trying to nail down the algorithm to determine the distance between
any two hexes when the coordinates are known.

I prefer a numbering where both x and y correspond to straight lines
of hexes, i.e., letting x increase (with constant y) by going right
and y increase (with constant x) by going 60 degrees down from right
(assuming (0,0) is top left corner).

This way, if you move in one of the three "natural" directions, you
either have constant x, constant y or constant (x+y).

That makes calculation of distances etc. easier, as you don't have to
sepcial-case on odd and even rows.

I assume you know the hex coordinates and want to find the distance in
number of hexes while moving across edges.

If you had used the alternative numbering I described above, the
distance is calculated as follows:

mydistance((x1,y1), (x2,y2))
= if x1>x2 then mydistance((x2,y2), (x1,y1))
else if y2>=y1 then x2-x1 + y2-y1
else max(x2-x1, y1-y2)

With the numbering shown on the webpage you sited, you can calculate
distance as follows:

= mydistance((x1 - y1 `div` 2,y1), (x2 - y2 `div` 2,y2))

I.e., convert to the simpler coordinate system and calculate distance
in that. You convert by subtracting half the y coordinate (rounded
down) from the x coordinate.