Inconsistent definitions for datum

[raffaem]

Here we first define datum as the origin of space or time. datum+measurement unit=reference system (section 2.1).

In section 2.3 the definition of datum changes, and includes not only the origin but also the scale and orientation (so it is now what was the reference system before).

It is confusing.

[edzer]

Would it help if I add "orientation" to the description in 2.1?

[raffaem]

To what?

[edzer]

to the first definition of datum.

[raffaem]

I don't understand how an origin (the first definition of datum) can have an orientation.

In $R^2$ we take as datum the point (0,0) with a left orientation?

In time, we take as datum the 1st of January 1900 with a forward orientation?

What does that mean?

[raffaem]

In any case the second definition also includes a scale (which I understand to be a unit of measurement)

[edzer]

The axes must have an orientation.

[raffaem]

In section 2.1 a datum with axes, scale and orientation is called "reference system".

If we remove "reference system" from section 2.1 and add the orientation and scale to the "datum" of 2.1, the definition of "datum" in 2.1 will be the same as the one provided in 2.3, but inconsistent with the one provided by wikipedia

[raffaem]

Or just remove the first paragraph of 2.3.

i don't think "geodetic datum" is used everywhere else and the reference system is already defined in 2.1 (just add an option "coordinate" before it)