Question

Creating an outline/single polygon of multiple polygons - Dissolve/ aggregate issue

  • 24 April 2019
  • 4 replies
  • 88 views
E

I have a few datasets of polygons and need outlines of the extents of each. Each polygon dataset has on average around 10,000 features and I need an outline of the extent of these to use in further processing stages e.g use as a clipper. Using the raw polygon data as the clipper instead is not an option due to how slow this makes the processing.

I have tried dissolving the polygons however this does not make a single polygon for the dataset as some of the features are not adjacent to each other. I then tried aggregating, which does achieve what I wanted however is useless for further processing as the aggregate is deaggregated by most processes - effectively slower than just using the raw polygons.

Hull building looked promising but does not accurately replicate the intricate boundary of each dataset.

In ArcGIS it is possible to dissolve based on a common attribute rather than requiring a shared boundary. Surely there is a way to replicate this process in FME?

4 replies

fmelizard
Rank
Userlevel 4
Badge +13

Hi @em_fme Maybe you want the BoundingBoxAccumulator to get the extent of a set of features? The Dissolver can also dissolve overlapping polygons - the boundaries do not need to shared. If the Dissolver was slow for you then you were likely using FME 2018 or earlier - please try FME 2019. There's also a HullAccumulator transformer which might do what you want.

E

Hi @em_fme Maybe you want the BoundingBoxAccumulator to get the extent of a set of features? The Dissolver can also dissolve overlapping polygons - the boundaries do not need to shared. If the Dissolver was slow for you then you were likely using FME 2018 or earlier - please try FME 2019. There's also a HullAccumulator transformer which might do what you want.

Thanks @danatsafe for the suggestions, but the bounding box accumulator and Hullaccumulator do not give the detail I am looking for. The outline of extent I'm hoping to produce should match the exact outline of the input data. I'm using FME 2018 and the dissolver can be quite slow. How can I configure the dissolver to dissolve regardless of boundary? Right now if features don't share a boundary they're output as separate features, so my 10,000 features in are output as about 130 features when I ideally want just 1 output.

samisnunu
Rank
Badge +7

@em_fme sorry It's too late to comment here, but I'm curious to know how you solved it, because I just encountered a similar situation to yours.

For me, it worked with just adding an Aggregator after the dissolver, and then output to SHP file.

 

nic_ran
Rank
Badge +11

Super late to the party on this one but just came across this thread in the course of something else I was looking at.

The AreaAmalgamator should do what you're asking for.... and you can supply a Group By attribute if required.

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