Unit Abbreviations

Håvard Dagsvik of Symetri implemented code to automatically generate a dictionary mapping the Revit DisplayUnitType to corresponding UnitSymbolType display strings.

If you are not clear about what these two Revit API enumeration mean, the developer guide description of units describes these classes like this:

• UnitType – type of physical quantity to be measured, for example length or force (UT_Length or UT_Force)
• DisplayUnitType – units and display format used to format numbers as strings or convert units (i.e. DUT_METERS)
• UnitSymbolType – unit symbol displayed in the formatted string representation of a number to indicate the units of the value (i.e. UST_M)

The Revit API help file RevitAPI.chm documentation says:

• DisplayUnitType Enumeration – The units and display format used to format numbers as strings. Also used for unit conversions.
• UnitSymbolType Enumeration – The unit symbol displayed in the formatted string representation of a number to indicate the units of the value.

The Building Coder already took a stab at this in two past articles:

• Unit abbreviations
• Localised unit abbreviations

The former implements a manually generated hard coded display of unit type abbreviation list for a selected subset of DisplayUnitType values.

The latter shows how you can use the LabelUtils to generate a list of localised abbreviations.

Håvard takes a new approach to automatically cover many more values without manual intervention.

In Håvard's own words:

I've been looking at extracting a complete list of unit abbreviations for each ParameterType and their DisplayUnitTypes. In total, roughly 210, I think.

I looked at what was around on your blog and elsewhere. Your manually generated list of unit abbreviations could be expanded to include all UnitSymbolTypes, not just the first 22. Anyhow, I decided to try something different.

What I do is this:

• Create a shared parameter file containing every parameter type.
• Attach these parameters to the ProjectInformation element.
• For every double parameter, set a value of 1.
• Then, for each parameter value, read the value string and isolate the unit abbreviation it contains.

In the end, the code produces a C# source file including the required using namespace statements and the actual Dictionary. That file can be imported directly back into Visual Studio to be used as an API. Here are both the complete Visual Studio Revit add-in project RVT_UnitTypes.zip and the C# module UnitAbbrevHandler.cs it generates.

It may be somewhat overkill; I'm not sure yet :-) If the list of abbrevs is not complete – though I think it is – it should be easy to tweak it more to get there.

This is related to an Excel export/import function. I export Revit parameters values to Excel, edit them there, and import the changed values back to the Revit elements.

In Excel, it's nice to have the unit abbreviations visible so you know what you are editing, e.g., meters or millimetres, Joules, gram Celsius or BTU for energy and specific heat, etc. That provides the use case for this dictionary. On export, we get the abbreviation from this predefined but auto-generated dictionary.

Originally, I thought it included all possible abbreviations, but it doesn't. The code could easily do that, but I only need one UnitSymbolType per DisplayUnitType. After all, lb/m3 and lbm/m3 represents the same thing.

The only situation I see in which this would matter is on parameter type Currency. The UnitSymbolType $ is obviously not the same as the UnitSymbolType £. But Revit is not a currency converter. In our case we only care about valid DUT's that can be fed into the UnitUtils.ConvertToInternalUnits function.

Tweaking this code, I guess you could create any other relations you might need, e.g., a complete Dictionary mapping "unit abbreviation to DisplayUnitType.

I hope this is useful to others as well.

Many thanks to Håvard for researching and sharing this!