1.How can I input Direct and Diffuse radiation in DIVA?
I've been away from the forum for much too long, and I apologize that no one answered your question. Being that so much time has passed, this is likely no longer useful to you; however, I would still like to respond.
1. DIVA is automatically splitting the radiation into direct and diffuse, if you already have the separated data, the Rhino toolbar GUI won't be useful. You can do this in Grasshopper by choosing the Perez Direct + Diffuse input for the sky type and zooming in to display the Dir and Dif inputs.
2. The Reindl method is being used to split the direct and diffuse.