Improper result from the “clipper”,

Hi,

 

 

Your feature are not perfectly matched

 

 

Use a scaler on the boundary, set origin to center. I used 1.01 just to see.

 

It will build what u want and also shows some artifacts due to not clean input.

 

 

This is result after scaling a bit.

 

 

Either u use scaling and then clip results, or better yet, take care that feature are better matched.

 

 

Gio

 

A good idea, as u do this often ....;), is to make a little workbench that checks topology of features before u do spatial processing.

 

 

Topology check would involve spatialrelating and output different relations: overlaps, crosses etc.

 

This u need to do per set and also between the sets.

 

 

Gio

Many thanks GIO,

 

 

Precisely, extracting Roads from the Boundary and Landuse is daily process at my workplace

 

 

Roads = Boundary – Landuse.

 

 

As the Boundary is often one polygon and Landuse contains multiple polygons, then in principle, why the clip fails? It should be able to subtract the polygons of the Landuse from the polygon of the Bounday to produce the Roads.

 

 

Separately, the FME detects the polygons correctly.

 

 

 

 

 

 

 

 

 

 

If the topology is the solution to my issue, how can it be integrated in the workbench?

 

 

Hi Jamal,

 

 

U can indeed use this topology builder, though i ment creating topology checks using a spatialrelator.

 

After the filter enter the boudnary to area input of topologybuilder.

 

Use geometrycoercer on the landuse, coerce to line. Enter this to line input of topologybuilder.

 

 

If us now set inspectors on the 3 outputs, you can see where it goes wrong.

 

In this case the boundary is not matched to the landuse.

 

U can see this by teh location where the topologybuilder puts nodes.

 

Missing nodes on "key" position tells you more or less that a clipper will not be able to clip there.

 

(thats why if u scale the boundary up, it does clip without error)

 

 

 

You can also use a dissolver on the landuse (no grouping) and then use clipper:

 

 

 

You now have the roads, but with bad objects at the edge.

 

 

Compare it with the topology and you can see that bad parts mis nodes at key positions, have crossing boudaryies etc. :

 

 

 

 

Thanks GIO,

 

 

Could you please share the workbench that you have already used to produce these outputs?