G-1 Aerial Surveys has produced a demonstration project based on the Stonehenge Site. The stereogram and topo-maps below are so you can view the site as we do in our measuring equipment. For those not familiar with viewing stereogram images please try the following. 

Just relax your eyes and let them drift slightly cross-eyed and the two images will drift into one in full stereo.  To make this easier notice the two flat stones at the top of each Stonehenge ring.  As your eyes relax you will see these two stones drift first apart then back together as your eyes cross more and more.  Use them to help bring the two images into one. 

It is stunning just how much more information becomes apparent in the image once you can see them in stereo.  This is why photogrammetric stereo instruments are superior for image analysis. These two images were clipped from two aerial photographs from two different positions in the sky.  When two such images are viewed in stereo in a photogrammetric instrument very accurate measurements can be made. This is the basic premise from which all photogrammetric processes result.

These images are from 18 micron scans of 11,800 : 1 photo scale 9" sq. photography.  The images were taken with a Kern Swiss 153mm focal length aerial film camera.  The image below is magnified 4 times from the original photos.  Stereo instrument measurements are routinely taken at a enlargement over 12 times. 

Below this stereogram is a section from the Topographic Survey conducted by G-1 Aerial Surveys.  Links to download both AutoCAD drawing(DWG) and Web Format(DWF) versions of the topographic study. 

People who own AutoCAD of course would want to look at the DWG file.  People without AutoCAD can still enjoy viewing the topographic study of Stonehenge by downloading the DWF version of the topo map.  A viewer for DWF files can be download from AutoDesk, a link to their download webpage is also provided below.

So pause on slide one and try it.  Then proceed through the rest.  Enjoy.