Problem

You need to swap Y and Z coordinates (indices 1 and 2) quickly in a point or point list.

Solution

In the grail.mstype module there are two utilities for quickly swapping points.

If you want to quickly swap points in a pointlist you would use the mstype.nPointList_YZSwap as follows,

>>> from grail import mstype
>>> pointList = [[1, 2, 3], [10, 20, 30], [100, 200, 300]]
>>> mstype.nPointList_YZSwap(pointList)
>>> print pointList
[[1, 3, 2], [10, 30, 20], [100, 300, 200]]

and if we re-run the routine we will get back our original point list.

>>> mstype.nPointList_YZSwap(pointList)
>>> print pointList
[[1, 2, 3], [10, 20, 30], [100, 200, 300]]

if you wanted to run it just on a point, you would do the following using mstype.nPoint_YZSwap,

>>> from grail import mstype
>>> point = [1, 2, 3]
>>> mstype.nPoint_YZSwap(point)
>>> print point
[1, 3, 2]

Both routines modify the contents of the point or pointlist in place. If you don't want to modify your data you can use the less efficient mstype.Point_YZSwap and mstype.PointList_YZSwap functions.

Dicussion

The reason you may have to swap these values is due to the fact that you are working closer to the graphical subsystem. In graphics the "z" coordinate corresponds to a direction that points out of the screen. Making this swap gives elevation its natural direction when viewing the data.