Inkscape

overlapping two-node straigh line paths disappear on union

Bug #166009 reported by Buliabyak-users on 2004-10-28

Affects		Status	Importance	Assigned to	Milestone
	Inkscape	Invalid	Low	Cth103

Bug Description

- draw a straight line path (just two clicks and Enter
in the bezier tool)

- ctrl+d

- select both paths and do Path > Union: they disappear.

Of note:

- this happens even if the paths coincide by only one
endnode, i.e. if after ctrl+d you move one of the nodes
of one of the paths with node tool, they will still
disappear

- this does not happen with curvilinear paths or with
paths consisting of two or more straight line segments
- they behave as expected (two paths turn into one)

- this happened in 0.39 too

- this is a minor but real problem because I have a
program which exports complex curves as sequences of
small straight <line>s; I want to turn them into a
single path and then simplify, but I cannot because
these lines coincide in their endnodes and thus
disappear on union.

Tags:

Revision history for this message

Buliabyak-users (buliabyak-users) wrote on 2005-07-19:

see also
http://sourceforge.net/tracker/index.php?func=detail&aid=1240704&group_id=93438&atid=604306

Revision history for this message

Aaron C Spike (acspike) wrote on 2005-09-09: byebyebool.svg

byebyebool.svg Edit (3.1 KiB, image/svg+xml)

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Aaron C Spike (acspike) wrote on 2005-09-09: byebyebool2.svg

byebyebool2.svg Edit (4.0 KiB, image/svg+xml)

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Peter Moulder (pjrm) wrote on 2005-11-12:

Union does a union of the areas, not necessarily a union of
the strokes, and not necessarily preserving direction,
thickness etc. of the strokes. It is not in general
possible for a single shape to embody the union of both the
areas and strokes of the input shapes (even ignoring
direction, stroke properties etc.). This distinction also
manifests itself with "self-overlapping" shapes (having a
region whose winding number is 2): the stroke around the
double-covered area is allowed to disappear.

A straight line segment has no internal area. As such,
doing a union of areas is allowed to discard that line
segment: whether the line segment is present or absent, the
shape has the same internal filled area.

One could envisage a slightly different operation where one
considered points on the edge to be part of the area. That
would be a feature request rather than a bug report; feel
free to re-open as such. (This wouldn't be enough to
prevent self-overlapping shapes from losing some of their
stroke.)

Use the Combine operation to do a union of strokes. This
seems to be what the submitter wants to do.

I suggest that the menu item should be called Area Union
instead (and similarly Difference, Intersection and Exclusion).

su_v (suv-lp) on 2011-10-11

tags:

added: boolops