I was a little confused by how units work in Draftsight, so now I think I’ve figured it out i thought I’d share.
The Model
They key thing to understand is that that the model, ie. the lines you’ve drawn, isn’t in mm or inches or feet, it’s just 1 Draftsight “unit”. When you change the settings related to units, nothing happens to model, it just changes what you see on the screen (in various places, like the cursor position in the status bar, or the length & co-ordinates of lines in the object properties).
The key setting is under Drawing Settings -> Unit System -> Length -> Type. Lets’ go through the options:
- Archtectural
- 1 Draftsight unit is interpreted as 1 inch, but it will display that as feet & inches if it’s more than 1 foot. Distances less than 1 inch are shown as fractions (where the denominator is a power of 2)
- Decimal
- No interpretation. You’re simply shown the number of Draftsight units, with decimals used for distances less than 1 unit.
- Engineering
- 1 Draftsight unit is interpreted as 1 inch, but it will display that as feet & inches if it’s more than 1 foot. Distances less than 1 inch are shown as decimals
- Fractional
- No interpretation. You’re simply shown the number of Draftsight units, but the instead of using decimals, fractions are used for quantites less than 1.
- Scientific
- No interpretation, but the number is presented in Scientific Notation
Blocks
Special handling is required for blocks because two designers could both draw something in different units. Alice draws in cm (ie. 1 draftsight unit = 1 cm) and Bob draws in inches (1 draftsight unit = 1 mm). If these drawings were simply combined without consideration of this, the scale would be different and they couldn’t be used together.
To get round this, Draftsight makes a record of the units when you create a block. The default for this is set in Drawing Settings -> Unit System -> Units Scale -> Block units format. When Alice creates a block, Draftsight records that unit in the block, so whenever it’s used Draftsight knows that 1 draftsight unit = 1 cm.
When Bob is drawing, he has the setting set to “Inches”. If he inserts a block made by Alice, Drafsight will recognise that his setting is different from the value stored in the block and scale it by the correct amount (2.54 in this case).
Dimensions
Dimensions deserve a mention while we’re discussion units. The key settings is Drafting Styles -> Dimension -> Linear Dimension -> Format. This has the same options as the first setting discussed above. This can be overridden on a per-dimension basis in the properties for the dimension.