Sometimes you get lucky, sometimes not

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I have wasted a fair amount of time today with a problem I solved the way I recommend to others: use a library. I needed to do a polygon offsetting in a program and I used what has worked for me in the past, the Java Topology Suite.

I did my thing and it almost worked perfectly:

However, I noticed a minor artifact once in a while. After some time I found that offset would sometimes did not work well as a weird line would appear crossing (line between to small circles) my beloved pumpkin instead or remaining on the outside (horizontal crossing was expected though).
I as not trying to do a full offset but only of the part whose normals is between 0 and 180 degrees, as this project is related to 3d milling. 

After a few hours of testing it all came down to a defect on the library (as far as I can tell) because with the same input data, but a smaller offset value, the operation was succesful as you can see below:

I was unable to find a proper forum to ask other users about this problem, so I will keep on using this library when the offset values needed are low but I will need to find a better choice for the future. If you know of a good choice I could use in Java I will like to know.

At any rate, here you have the data points in case you want to have a look.



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