# Coordinate system

Source: https://meptools.com/tools/plant-room-studio/docs/coordinate-system/

Plant Room Studio uses one consistent convention across the 2D plan, the inspector, and the 3D
model. Understanding it makes coordinates and rotations predictable.

## Units

All internal dimensions and coordinates are in **millimetres**. Room sizes, equipment
footprints, and clearances are all mm values.

## Origin and axes

- The origin sits at the **bottom-left** corner of the plan.
- **Positive X** runs to the **right**.
- **Positive Y** runs **up** the plan.

So an equipment position of `(2400, 1500)` is 2400 mm to the right of the origin and 1500 mm up
from it. Because Y points up, pressing **Arrow Up** moves a selected item toward the top of the
plan.

## The vertical (height) axis

The plan is a top-down floor view, so height doesn't appear in 2D. Each equipment item still has
a **height** (used in the 3D model) and a **mount elevation** above finished floor. Floor-standing
items sit at 0 mm; **wall-mounted** items default to **300 mm** above finished floor.

## Rotation

Equipment rotation is measured in degrees, **clockwise when viewed from above**. A rotation of
0° leaves an item in its library orientation; **Shift+R** rotates the selection by 90°. The 3D
model and all clearance geometry follow the same rotation, so what you validate in plan is what
you see in 3D.

Next: build a [room](/tools/plant-room-studio/docs/rooms) to sit your equipment in.