Wednesday, June 15, 2005

Revit - Shadow Diagrams

Part of the work I do, in making submissions for approval for construction for a building, is to prepare shadow diagrams. The diagrams are to show the impact the building will have over adjacent properties.

For new buildings, the ability to be in a roof plan view in Revit and cast shadows from the building onto the ground plane is really wonderful. This is achieved using the >Advanced Model Graphics<>View Properties< menu.

Here, it is possible to setup and save various locations, time of day and day of year options to apply to the model. To prepare a shadow, I duplicate the "SitePlan" view, which shows the roof, and topography, and save it as say "Shadow 9-00am 22nd June" (for the Winter Solstice - I am down under in Australia!). Then I go to the >View<>Advanced Model Graphics< I set the time of day, location and date for the shadows to be cast. The software then calculates and casts the shadow.

One thing to be aware of, is to ensure you have set the correct direction for North. I usually rotate my view to "True North" and lay out my shadow diagrams on sheets this way.

Graphically, the only problem I have had with this method, is that shadows are also cast over parts of the building model. So, instead of a simple shadow diagram, which shows the proposed building in outline, and just the extent of shadow cast OUTSIDE the building envelope, I get shadows over the ground AND over my building. Which makes the shadows look much worse!

The solution I have found to this is to create a white "Filled Region" over the my building. This essentially blanks out the building and the shadows underneath, and shows what I want: the extent of the shadow cast by the building's envelope. It makes a nice and simple diagram to read.

I then duplicate this view with detailing, and apply a different shadow criteria for time of day and date etc. This way I build up my set of shadow diagrams very quickly.

For existing buildings on adjacent sites, we would generally "blank" out the extent of shadow cast over that building's footprint cast by our new building. So using the same "Filled Region" method described above, I would draw a filled region over the adjacent buildings shown on the survey plan. This then simplifies the shadows even more to show the extent cast by the new building's envelope, and the existing adjacent buildings shown "blanked" out so the shadow wraps around these buildings.

The problem for me came when I had to cast shadows for additions to an existing building. Under these circumstances, we are required to show, on the same diagram, the extent of shadow cast by the existing building, the extent of shadow cast over and above this shadow by the new building. In other words, two shadows on top of each other with one shadow "subtracted" from the other shadow.

When first using Revit I had no idea how to do this. But I have since discover a very elegant way that works well.

When doing additions to a building, it is important to use Revit's Phases and Phase filters. Draw the existing building using the "Existing" phase, and then make the changes to the building using the "New Construction" phase. These are accessible under the "view" menu right at the bottom. Phases are very powerful, and a subject all on their own.

Once you have documented the building using the "existing" phase and the "new construction" phase, it is possible to "switch" between seeing the existing building and seeing the completed building just by adjusting the phase filter.

To cast shadows as required for the existing compared with the new, follow the methods outlined above. Except you will have a shadow plan for say 9:00am 22nd June which is a "new construction" phase, showing the total shadow for new and old, and a separate plan for 9:00am 22nd June Existing, with the phase filter set to "existing". In other words, you have created two shadow views, one phased for "existing" and one phased for "new construction". I also make sure I have placed the filled regions over the plans as described above to "blank out" the building outlines.

Under the >Advanced Model Graphics< menu, it is possible to adjust the intensity of the shadows cast. For the method I am describing, I cast the existing shadows quite dark at say 60% intensity. The new construction shadows I cast much lighter at say 30% intensity. This is so that on plan, the shadows will read differently to each other. It also means that the existing shadows will sit "on top" of the new shadows, because they are cast much darker.

You now have two shadows for the same time of day; existing and new work. You can place these on a sheet one view exactly on top of another view.

In sheet view, bring in the existing shadow plan, and lay it out on the sheet where you want it to be. Next, bring in the new construction shadow plan, and lay it out exactly on top of the existing plan. Revit helps you with this by giving you a green dotted crosshair when the two plans are exactly aligned.

What you will see now is your new building shadow in light grey, and your existing shadow in a darker grey together. You will also have you buildings on the site "blanked out" with the filled region, giving a simple shadow comparision of existing and new construction.

I hope this helps anyone who is facing the same challenge!

Write me if you want to know more, of if you have any queries.

Best wishes



Blogger Subir said...

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9:19 PM  

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