Division by zero in iterate_4d

[Algunenano]

There is a typo calculating distances in the z-axis.

It appeared as an error as a division by zero

lwgeom_median.c:111:17: runtime error: division by zero

in the test

do_median_test("MULTIPOINT ZM ((0 -1 0 1), (0 0 0 1), (0 1 0 0.5), (0 1 0 0.5))", "POINT (0 0 0)", LW_TRUE, 1000);

Github PR: ​https://github.com/postgis/postgis/pull/196

[komzpa]

In 16341:

Fix bug in iterate_4d.

Patch by Raúl Marín Rodríguez.

Closes #3997
Closes ​https://github.com/postgis/postgis/pull/196

[strk]

Such fixes should come with a testcase. Can you please add one Raul? Or Komzpa ?

[Algunenano]

Working on it. It's really tricky you need a really specific geometry. Also the division by zero is still possible.

[Algunenano]

PR with the test and removing the possibility of division by zero: ​https://github.com/postgis/postgis/pull/198

[pramsey]

In 16366:

lwgeom_median: Avoid division by zero
(Raúl Marín Rodríguez)
Closes #3997
Closes ​https://github.com/postgis/postgis/pull/198

[Algunenano]

As @komzpa commented in the GH issue (​https://github.com/postgis/postgis/pull/198#issuecomment-362911760) the ticket introduced here is failing.

Here is the PR with the fix (basically change how the check is done, from comparing coordinates to comparing sum of distances): ​https://github.com/postgis/postgis/pull/205

[Algunenano]

Fixed with ​https://trac.osgeo.org/postgis/ticket/4012

[Raul Marin]

In 16579:

Fix bug in lwgeom_median and avoid division by zero

References #3997
Closes ​https://github.com/postgis/postgis/pull/244

[Raul Marin]

In 16580:

Fix bug in lwgeom_median and avoid division by zero

References #3997
Closes ​https://github.com/postgis/postgis/pull/245