libgeos/libgeos — pull request #40 by mloskot (2014-12-01 15:36:51+00:00)
Title: Port DoubleDouble and CGAlgorithmsDD support

This is a prototype of **DoubleDouble** support for GEOS, as an analog to JTS DoubleDouble.

The PR includes:
* [ttmath](http://www.ttmath.org ) 0.9.3 library
* [doubledouble](http://www.boutell.com/fracster-src/doubledouble/doubledouble.html) 2.2 library (GPL!)
* Minimal port of JTS `CGAlgorithmsDD` class
* DoubleDouble (DD) support can be switched to either ttmath or doubledouble at build-time, see detailed logs of the commits below.
* A bunch of curious test cases:
* Test case of `orientationIndex` method for orientation vs inverse (see comment in
[RobustDeterminant.java/RobustDeterminant.orienationIndex](http://sourceforge.net/p/jts-topo-suite/code/626/tree//trunk/jts/java/src/com/vividsolutions/jts/algorithm/RobustDeterminant.java))
* Test cases of **test on segment** vs **test on vertex of segment** based on geometries in both formats, WKT and WKB. See commit logs for explanation of the **curious** results obtained using both JTS and GEOS (with DD support), for WKT vs WKB (!)

This PR is directly related to the problems discussed in this GEOS ticket http://trac.osgeo.org/geos/ticket/591

Next, I'm going to contact @dr-jts if he would be willing to comment on the JTS results obtained for the **test on segment** case.