Alidade

 This is final Alidade for the Exploratorium is based off of the Osborne Fire Finder and my initial cardboard model.  It is 19.5'' in diameter and composed of machined aluminum, machined phenolic as well as glass and acrylic.   It's seen sitting in the Pier 17 window (in SF) on our mock up rail, so the map in this case does not correspond to the viewable landscape as it will when placed in the Exploratorium's new Observatory Gallery at the end of the pier and one story up. Below are a few additional preliminary photos of the Alidade.

 As these were the first photos taken of the finished alidade, the map disk and point ring are made of paper and not the etched and printed aluminum that will be in the finalized exhibit. On the upper part of the map disk you can see a map of the San Francisco waterfront. On the lower part there is the color coded zone diagram which separates the view into various districts. The acrylic ruler that spans the two sights indicates the line of sight as seen in plan (normal map) and in section (zone diagram). The ruler is also graduated to indicate the approximate distance between the observer (at the center of the map) and the landmarks being viewed on the water front map. The small pocket in the lower sight indicates the initials of the landmarks being viewed so they can be looked up in an accompanying book which will provide information on the landmark's historical context and how it relates to the district in which it resides.   Currently, the design of the book is in progress, so is not pictured here.      

Heres another detail of the map and the line of sight rule.

Here is a view of the near sight and the point indicator gauge, the bearing angles are also indicated below the zone diagram.

A view of the far cross hair sight.