I spotted the ShewchuksDeterminant class in the development trunk for the JTS.
Congratulations on a truly ambitious bit of work. A Java port of Shewchuk's
original robust predicate code could not have been an easy task (looking at
the comments, I see you even found a bug in the original). Also, I think the
JTS version is cleanly coded and the developer (Tomas Fa?) made some good
design choices.
I have some questions about the code.
First off, the ShewchuksDeterminant class does not appear to be integrated into
the main source branch. Will it be moving into the standard JTS distribution?
If so, when?
Second, I notice that the implementation does not use the "strictfp" keyword.
The strictfp keyword is sometimes used in modules that perform extended
precision floating-point operations (for example, JTS's DD.java class). Before
I discovered the JTS implementation, I was thinking about doing my own Java
port of Shewchuk's "robust predicates" and I wondered whether this would be
necessary. Shewchuk mentions issues with Intel CPUs at
http://www.cs.cmu.edu/~quake/robust.pc.html noting that they "use extended
precision internal floating-point registers [that] defeat Dekker's standard
techniques for computing the roundoff error for a floating-point operation."
Could this issue affect the current implementation? Did the JTS implementers
look in to this issue and decide it wasn't necessary? If so, I would be
interested in hearing more about their findings.
Finally, I was wondering whether there were plans to implement Shewchuk's
"inCircle" predicate. While the JTS TrianglePredicates class does implement
inCircle methods, a full-blown Java implementation of Shewchuk's techniques
would be a valuable addition.
Gary
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