2.1. FILE UNITS


DIVA daylight models are scale dependent. The reasons for this are twofold. First, DIVA's outputs — such as sDA and lighting energy — often require an accurate accounting of distances and areas. And second, DIVA's inputs — like sensor spacing — often use real-world distances as defaults, and therefore need to know what units to assume. The source of this information is Rhino's units setting, which can be accessed from the File menu under Properties:

Set model units using Rhino's document properties form

Grasshopper definitions do not have unit systems of their own, so unit information is always gathered from the active Rhino document. To see this in action, you can test the effect of extant Rhino units when adding a Grid component to the Grasshopper canvas:

DIVA sets inputs to real-world distances based Rhino's unit system

Note that these parameter values will not change if you switch Rhino units after a component has been added to the canvas. Because of this data persistence, it is important that you choose a unit system in Rhino before setting up your Grasshopper definition. You should also avoid switching units midstream, as performing scaling operations on Grasshopper definitions is impossible.

Finally, while all unit systems are permissible for DIVA daylighting models, the same is not true for Archsim energy models. If you intend to use a document for Archsim analysis, you should work in Meters, which is the native unit system of EnergyPlus.