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Can't build polygons


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I have a coastline with some islands as polylines from AutoCad (.dwg file). I opened it in SMS to build the mesh, however when I try to Build Polygons only those referred to the islands are created. Why can’t SMS (10.0) create the polygon for the coastline? Can it be related with the Clean options before doing the Build Polygons? Selecting “snap nodes and vertices” and changing the tolerance may solve the problem, but changes a lot the format of the islands!

Thank you for your help.


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Usually this is caused by a "gap" in the polygon. Make sure that all of the arcs in the outer polygon are connected. This can be done by zooming in and examining the ends of each arc or by cleaning.

Merge all arcs - easier to see gaps:

* Switch to the "Select Feature Point" tool

* Right click and "Select All"

* Menu command "Feature Objects | Vertices <-> Nodes"

You can now turn on the feature points in the display options and it should be easy to spot any discontinuities in your coastline.


If you don't want to clean the islands, you may want to clean only the coastline:

* Make two copies of the coverage (right click command on coverage in project explorer)

* Rename the coverages "Islands" and "Outer Poly"

* Delete the outer polygon arcs from the "Island" coverage

* Delete the island arcs from the "Outer Poly" coverage

* Use the clean options to clean the "Outer Poly" coverage

* Select both coverages in the project explorer (use the shift key and left click) and merge them (right click command on coverage in project explorer)

* Build polygons

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