I'm doing something wrong.
I tried your function and I get almost 100%. The function within seems to work
on the bounding rectangle not the shape.
With this mod, I do get 100 percent:
function coverage obLID
set the filled of obLID to true
put the rect of obLID into r
repeat with x = (item 1 of r) to (item 3 of r)-1
repeat with y = (item 2 of r) to (item 4 of r)-1
put x,y into pt
if within(obLID,pt) then add 1 to isIn
add 1 to all
end repeat
end repeat
return isIn/all
end coverage
I subtracted 1 from the right and bottom.
Dar
On Jun 6, 2013, at 5:39 PM, David Epstein wrote:
> In order to properly adjust the relative area of two dissimilar polygons, I
> thought I would use a function to determine the fraction of each polygon's
> rectangle that is covered by the polygon.
>
> function coverage obLID
> set the filled of obLID to true
> put the rect of obLID into r
> repeat with x = (item 1 of r) to (item 3 of r)
> repeat with y = (item 2 of r) to (item 4 of r)
> put x,y into pt
> if within(obLID,pt) then add 1 to isIn
> add 1 to all
> end repeat
> end repeat
> return isIn/all
> end coverage
>
> This seems to work as expected, but I am perplexed by the fact that when I
> resize an object keeping its proportions constant (drag a corner with the
> shift key down; or script this) I get a surprising variation in the result.
> E.g., a fairly simple shape I tried went from 0.48 coverage up to 0.59
> coverage when I shrank its dimensions by about two-thirds. With tens or
> hundreds of thousands of pixels being sampled in the calculation, I would not
> expect this variation.
>
> Many thanks for any insights or suggestions.
>
> David Epstein
>
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