"invalid" geometries in shape data

Hi,

I'm interested in exploring the details of kinds of errors and warnings
that are seen from the underlying geometry lib (GEOS) for spatial data in
R.

I would like to also have a collection of  examples with actual data and
reproducible code.

(The underlying theory and definitions and source code are all open and
available, I'm looking for examples).

The kinds of errors I'm talking about come from the GEOS library under the
hood, and this is more or less the same in the sp/rgdal as well as the new
sf family.

Here's one example, this data set is not valid because of at least one
"polygon self intersection", basically the ring winds back on itself:

library(maptools)
data(wrld_simpl)
rgeos::gIsValid(wrld_simpl)
[1] FALSE
Warning message:
In RGEOSUnaryPredFunc(spgeom, byid, "rgeos_isvalid") :
  Ring Self-intersection at or near point -95.902496339999999
66.946641920000005

I'd appreciate if you could send me similar examples, preferably
reproducible with code but links to existing emails and online posts are
welcome too. Feel free to construct examples from scratch that reproduce a
particular warning/error.

If you like, you can use the Github Issues mechanism here, or just email
them in reply.

https://github.com/r-gris/toposhop/issues

Cheers, Mike.

Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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