# The Complexity of Drawing a Graph in a Polygonal Region

• Anna Lubiw
• Tillmann Miltzow
• Debajyoti Mondal
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 11282)

## Abstract

We prove that the following problem is complete for the existential theory of the reals: Given a planar graph and a polygonal region, with some vertices of the graph assigned to points on the boundary of the region, place the remaining vertices to create a planar straight-line drawing of the graph inside the region. A special case is the problem of extending a partial planar graph drawing, which was proved NP-hard by Patrignani. Our result is one of the first showing that a problem of drawing planar graphs with straight-line edges is hard for the existential theory of the reals. The complexity of the problem is open for a simply connected region.

We also show that, even for integer input coordinates, it is possible that drawing a graph in a polygonal region requires some vertices to be placed at irrational coordinates. By contrast, the coordinates are known to be bounded in the special case of a convex region, or for drawing a path in any polygonal region.

## Notes

### Acknowledgment

We would like to thank Günter Rote, who discussed with the second author the turn gadget in the context of the $$\textsc {Art~Gallery~Problem}$$.

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## Authors and Affiliations

• Anna Lubiw
• 1
Email author
• Tillmann Miltzow
• 2
• Debajyoti Mondal
• 3
1. 1.Cheriton School of Computer ScienceUniversity of WaterlooWaterlooCanada
2. 2.Université libre de Bruxelles (ULB)BrusselsBelgium