Querying a line string for whether it's convex/closed gives inconsistent results

[dsogari]

I may be mistaken about this, but consider the following piece of code:

OGRLineString *line = new OGRLineString();
line->IsConvex();      // gives true
line->get_IsClosed();  // assertion failure (#1)

line->addPoint(0, 0);
line->IsConvex();      // gives true
line->get_IsClosed();  // gives true

// counter-clockwise one-sided square (not closed)
line->addPoint(1, 0);
line->addPoint(1, 1);
line->addPoint(0, 1);

line->IsConvex();      // gives false (#2)
line->get_IsClosed();  // gives false (ok)

line->addPoint(0, 0);  // close ring
line->IsConvex();      // gives false (#2)
line->get_IsClosed();  // gives true (ok)

line->reversePoints(); // make it clockwise
line->IsConvex();      // gives true (ok)
line->get_IsClosed();  // gives true (ok)

• Remark 1: why is it that an empty line string cannot be queried for whether it's closed, while it can be queried for whether it's convex?

• Remark 2: why is it that a line string is convex when its points are laid out clockwisely, whereas it is not convex when they are laid out in counter-clockwise order (either closed or non-closed)?

An example .cpp file is attached for convenience.

[dsogari]

test file

[Even Rouault]

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