Hi, just a note: looks like algorithm fails with "spikes" or "whiskers" i.e. single pixel protrusions, kind of:

fun assign_points() {

# .......
# .#......
# .#......
# .####...
# .####...
# .####...
# .######.
# .#......
# .#......
# ........

return [
[1,1],
[1,2],
[1,3],[2,3],[3,3],[4,3],
[1,4],[2,4],[3,4],[4,4],
[1,5],[2,5],[3,5],[4,5],
[1,6],[2,6],[3,6],[4,6],[5,6],[6,6],
[1,7],
[1,8],
];
}

[download]

And:

  012345
: #      :   0
: #      :   1
: ####   :   2
: ####   :   3
: ####   :   4
: ###### :   5
: #      :   6
: #      :   7
Type [CR]

  012345
: #      :   0
: #      :   1
: ####   :   2
: #oo#   :   3
: #oo#   :   4
: ###### :   5
: #      :   6
: #      :   7
Type [CR]

  012345
: #      :   0
: #      :   1
: ##AB   :   2
: #  C   :   3
: #  D   :   4
: ####EF :   5
: #      :   6
: #      :   7
Type [CR]
[Resulting Outline]
[1,2],[2,2],[3,2],[3,3],[3,4],[4,5],[5,5],

[download]

I thought polyline must retreat its steps along such protrusions, cf. output from my program:

........
.0......
.1......
.2765...
.3..4...
.4..3...
.589012.
.6......
.7......
........

[download]

Plus, not sure if it's safe to always hope for horizontal AND "interior on the right if moving CW" edge present -- circles, upside-down triangles, etc. -- but, it's your application and you know what input to expect.

Edit:About triangles. + Not sure about the rule. But simple 3x3 triangle fails.

In reply to Re^8: Polygon Creation -- Request for Algorithm Suggestions by vr
in thread Polygon Creation -- Request for Algorithm Suggestions by golux

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