Chart Problem

[Judd]

On a 'spiders web' chart made up of regular triangles (making a regular polygon), how do you work out the value at any given point, if you know the coordinates of the point and the coordinates of the chart centre?

(Obviously you know the range of the chart too)

I did a little diagram...

Its not necessarily a hexagon btw

[NoteMe]

What do you mean by value of the point. Do you mean the coordinates?

[Judd]

Take the hexagon chart as an example.

The chart has a scale, say 0 at the origin, 100 at the outside point.

So, for instance, the 'value' of 50 describes a smaller hexagon around the mid-point of the chart lines.

So say you display the chart on a screen and you want to display the value under the mouse pointer. You have the coords of the chart origin and the coords of the mouse pointer, how do you use those to calculate the 'value' at the mouse pointer....

Clear?

As mud probably!

[opus]

No, not clear.
What would be the value in your little diagram?, that might help!

[NotLKH]

There are many ways to create mappings, and to intertranslate between is difficult, if you don't provide a clear explanation of your before and after.

However, even though you claim you're not mapping hexes, perhaps this thread might provide some help?


-Lou

[Judd]

I redid the pic to try and make things clearer.

But I want to calculate this from the coordinates, and the knowledge of the number of sides in the polygon (and hence the angles in each triangle).

The value is a+b, which is relatively easy to get (I think), but how do you translate this if the point isn't in the first segment?

(Also, the coordinate system is not related to the graph scale, so a ratio will have to be used, that is ratio of a+b to the full scale of the chart).

[sql_lall]

hmmm...am i correct in thinking that you want the 'value' (a+b) given the (x,y) co-ordinates of the point?

In this case:
|a| = |y|
tan(@) = |x|/|b| => |b| = |x|/tan(@)

=> |a| + |b| = |y| + |x|/tan(@)
=> (a+b) = value = |y| + |x|/tan(@)

where |x| = abs(x) = (x>0) ? x : -x;