AreaOnAreaOverlayer tolerance?

HI @daniel, if you need to control the coordinates precision of feature geometries, consider using the CoordinateRounder transformer.

Note: You can specify the number of decimal places of coordinate values using the CoordinateRounder, but it doesn't mean changing the computational precision (i.e. the number of significant digits). Even if you round coordinate values with the transformer, FME still calculates spatial relations by the full precision of 64 bit floating point number.

Exactly, this is also the case with e.g. ArcGIS and the tolerance/precision settings defined in the feature classes; FME does not use them.

@daniel, have you tried "Segment Snapping" for the Snapping Type parameter of the Snapper/AnchoredSnapper?

Maybe try to buffer both area layers with e.g. -0.001m before sending them trough the AreaOnAreaOverlayer. This makes the areas slightly smaller and therefore eliminating slivers within this 0.001m range at the edges.

My current process is piping the 2 layers (each for a tracking attribute added) into the AreaOnAreaOverlayer then using a tester to keep areas of overlap (where both tracking attributes = 1). For this work space it is producing about 3700 polygons whereas when I do a spatial intersection for the same two layers using GeoMedia software it produces about 1400 polygons. GeoMedia I know uses a tolerance of 0.0001 metres. @Mark2AtSafe

Using the CoordinateRounder after the AreaOnAreaOverlayer did not reduce the number of polygons when used in combination with the Snapper transformer (using "Segment Snapping" and Snapping Tolerance of 1 metre). When I add another Snapper ("Vertex Snapping") it does reduce the polygon count but only by a couple of hundred. @bakkermans

Using a negative buffer on both layers does reduce the polygon count but again not by a substantial amount. Only if I set each bufferer to minus 1 metre and even then it is still producing more polygons than in GeoMedia which has a tolerance of 0.0001 metres.

@erik_jan

Yes, I have done that in the past - using a tester to remove slivers based on their area. However, I don't think this is an ideal solution. What I want to achieve is the same result as other GIS software or database where a tolerance can be defined for example as @egomm

mentioned in oracle using intersect a tolerance can be set.

I don't think it is possible to produce exactly the same result in FME. There are lots of steps you can take to improve the results, as mentioned above, but I don't think you'll ever get an identical result.

In the past I've ended up stringing two workbenches together, one which writes the data into oracle, the second which starts with a sql creator which performs the intersection within oracle and continues from there.