Web-based drawing overlays with annotations

I'm remodelling a house. The drawings of the architect and the acoustician don't match and they have trouble incorporating each other's adjustments. We'll have similar issues when FiFi LaChintz does the interior decorating and Groundskeeper Willy does the landscape design. So I want a Web-based drawing presenter that lets you place and overlay multiple images in different formats, adjust their translucency (like onion-skinning in Macromedia Director), and make annotations.

So in the stack of images

• June plan.dwg
• speaker_placement.jpg
• Sept plan.dwg
  

you'd have annotations between layers like

• "The equipment racks have moved East."
• "You have the speakers centered on the window bays, not the room"
• "The cable run in your sketch have to go through the rafters in mine"
  

The program doesn't have to do any interactive drawing of its own, just present a layered set of drawings.

It's similar to Google maps with an arbitrary set of graphics from the Web.

A server would do image conversion (few browsers can render .dwg files).
I'm not sure if you can do the overlays on the client (png files with different alphas in overlapping divs)?

Maybe Autocad has this, but their Windows-only viewer seems no longer free.
Maybe Madocromebedia Acrobat has this, but it's hardly Web-based.

Categories: web, Web2.0, house, software