Opened 13 years ago

Closed 13 years ago

#1775 closed defect (fixed)

False negative motion collision detection in ST_ChangeEdgeGeom

Reported by: strk Owned by: strk
Priority: high Milestone: PostGIS 2.0.1
Component: topology Version: 2.0.x
Keywords: Cc:

Description

While playing with topology edge simplification I encountered a case in which ST_ChangeEdgeGeom allows to change an edge geometry from A to B but doesn't allow it to move back from B to A.

Looking at the movement visually I can see that the movement should never be allowed.

Attachments (1)

collision.png​ (4.9 KB ) - added by strk 13 years ago.

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Change History (6)

by strk, 13 years ago

Attachment: collision.png​ added

comment:1 by strk, 13 years ago

from orange to green is allowed, from green to orange it is not: ERROR: Edge motion collision at POINT(699288 6901218)

The collision point is correctly reported as the island you see near the bottom.

comment:2 by strk, 13 years ago

I confirm that the result of the bogus allowance is an invalid topology (wrong face linking).

comment:3 by strk, 13 years ago

Summary: Asymmetric undetected edge motion collision → False negative motion collision detection in ST_ChangeEdgeGeom

comment:4 by strk, 13 years ago

Found the culprit: ST_SymDifference(EMPTY, POLY) returns EMPTY -- filed #1776 for this. Once that one is fixed this one should also be. We'll want a testcase for this anyway.

comment:5 by strk, 13 years ago

Resolution: → fixed
Status: new → closed

r9641 fixes ST_SymDifference and r9642 regress-tests this specific use case.

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