Add hints for ordering of -matrix arguments for pcl_transform_point_cloud

[themightyoarfish]

Intuitively I would have assumed row by row ordering, but actually you have to use column by column.

[themightyoarfish]

Although maybe this depends on the Eigen storage order used during pcl or client project build?

[mvieth]

No, seems like that does not matter

• https://github.com/PointCloudLibrary/pcl/blob/master/tools/transform_point_cloud.cpp#L324
• https://eigen.tuxfamily.org/dox/classEigen_1_1DenseCoeffsBase_3_01Derived_00_01WriteAccessors_01_4.html#ae6ba07bad9e3026afe54806fdefe32bb

[larshg]

Intuitively I would have assumed row by row ordering, but actually you have to use column by column.

Yeah, default for Eigen is col-major:
If the storage order is not specified, then Eigen defaults to storing the entry in column-major. This is also the case if one of the convenience typedefs (Matrix3f, ArrayXXd, etc.) is used.

https://eigen.tuxfamily.org/dox/group__TopicStorageOrders.html