FROM

Database Management Reference Manual

Expressions : Positions, Directions and Orientations in Expressions : FROM

In some cases we require an offset from a fixed point, other than the position of an item. For example, a point or attribute.

The FROM syntax is used for this. We may still use WRT in combination with FROM, but in this case the WRT is only used to determine the axis direction and not the offset, since the offset is specified by the FROM part.

Consider the following:


Item	Comments
A SITE at (0,0,0)	With default (World) orientation
A ZONE at (100,0,0)	With default (World) orientation
An EQUIPMENT at (100,0,0)	With orientation ’N IS E
A BOX at (-100,0,0)	With default (World) orientation

The result of Q (N 100 WRT /* FROM /BOX1), shown as ⊗ in , will depend on the current element.


Location	Result
World, Site, and Zone	(200,200,0) since the offset of N100 is applied in world axis rather than /BOX1 axis.
Equipment	(100,200,0). Note: the default axis for the result is the Zone.
Box	(200,0,0), because the default axis for the result is the Equipment.

The result of ’Q (N 100 WRT /BOX1 FROM /* ) is different:


Location	Result
Site and Zone	(100,0,0)
Equipment	(0,0,0)
Box	(0, -100, 0), because the axis for the result is the Equipment.

The result of ’Q (N 100 FROM /* )’ is different yet again.

For this we cannot mark an absolute point on the diagram since the default WRT will vary with the current element. In fact for the SITE, ZONE, EQUI the point ⊗ is marked in , and for the BOX the point coincides with the ZONE.


Location	Result
Site and Zone	(0,100,0)
Equipment	(-100,100,0), because the default result axis is the Zone.
Box	(0, -100, 0), because the axis for the result is the Equipment.

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