Dimensions
Use a dimension to fix a distance, a radius or an angle to a value you choose. Select the geometry, press the key, type the value.
A dimension is a constraint with a number in it. It removes a freedom like any other relation.
The reference
| Dimension | Key | Select | Measures |
|---|---|---|---|
| Dimension | D | 1 line | The line itself (the field inside the popover is labelled Length) |
| Distance | D | 2 points | Straight-line gap |
| Horizontal distance | — | 2 points | The x gap only |
| Vertical distance | — | 2 points | The y gap only |
| Distance ∥ | D | 2 lines | The gap between two parallel lines, measured perpendicular to them |
| Distance point → line | D | 1 point + 1 line | Perpendicular distance |
| Distance point → curve | — | 1 point + 1 curve | To the nearest point on the curve |
| Distance line → curve | — | 1 line + 1 curve | Between the two |
| Radius | R | 1 circle or arc | Radius |
| Diameter | D | 1 circle | Diameter |
| Angle | A | 2 lines | The angle between them |
D is shared on purpose. Length, distance and diameter are the same intent, so press D and let the selection decide which one you get.
Radius or diameter?
Match the thing you are making. A hole for an M4 screw is specified as a diameter, so dimension the diameter. Then the number in your sketch is the number in the fastener table, and nobody has to halve anything. A fillet is specified as a radius. Getting this right removes a whole category of arithmetic mistake.
A number, a name, or a formula
Here is where a dimension stops being a measurement and becomes a control. Every dimension field takes any of these:
- A value, such as
30. - A parameter that already exists, such as
WIDTH. The dimension now follows whatever that parameter says. Names are case-insensitive and stored upper-case, sowidthandWIDTHare the same parameter. - A new parameter, declared on the spot, such as
WIDTH(30). The parenthesised number is its starting value. The field commits, the parameter is created, and the dimension is bound to it. Declare parameters this way to name something while you are drawing it. - An expression, such as
WIDTH / 2 - CLEARANCE. Arithmetic over other parameters.
On the canvas the label keeps showing the number, not the name, because a sketch dimension carries its expression rather than a visible link. To see what is driving a dimension, reopen it: the field shows the name you typed. To prove the binding, change the parameter and watch the geometry move.
This is the mechanism behind every configurable part in Kapy. A model whose dimensions are all literal numbers can be edited. A model whose dimensions are named and related can be resized. Change one value and the whole part follows, including the features built on top of it.
The dimension on the canvas
The label is turned along its own dimension line and set just off it, on the side away from what it measures, so the line no longer runs through the text and a short dimension no longer prints over the very geometry it is measuring. A vertical one reads bottom-to-top, the way a drawing is read from the right, and none of them come out mirrored.
Like a constraint chip, a dimension is bare at rest — the value on a wash — and grows its border only under the pointer. And it can be dragged. The label slides along the dimension line, and pulling it away carries the dimension line, its extension lines and its arrows with it, so it stays attached to what it measures. The placement is stored along the dimension's own line rather than as a point on the plane, so it survives a zoom, a change of plane and the geometry moving underneath it, and the gesture never touches the sketch: the document is written once, when you let go.
An angle has one more control. Two crossing lines make four angles, and which of them the dimension means is a four-way selector in its popover rather than something decided once, out of reach, when you drew it. The number on the label is the angle the arc actually sweeps, so an obtuse angle reads 145°, not 35°. The exception is an angle bound to a parameter or a formula: that one keeps printing the parameter's own magnitude, because that is the number you named and the number you edit in the parameter panel.
Driving vs measured
Dimensions in a sketch are driving. They set the geometry rather than describe it. To find out how long something is without constraining it, select it and read the status bar, which measures whatever you have picked without touching the sketch.
See also
- Geometric Constraints: the relations without numbers
- How the Solver Works: why a fully constrained sketch is the goal
- Extrude and Cut: where a parameter-driven sketch pays off