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.
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