Surface error: photogrammetry

Measuring the panels with photogrammetry:

• Reflective targets are placed on each panel (38000+)
  
• Pictures of the dish are taken from the top of each tower (9" film).
• Films are measured on an optical measuring machine (takes about 3 months).
• Back fit for camera position and determine position of each target (no distance scale, only angles).
• Survey (using a theodolite) some reflectors to put a distance scale on the measurement.

• North/south support cables have tieback cables that can be adjusted to pull the cable catenary close to the spherical shape.
• Each corner of 4 panels can be adjusted vertically.
• Iterate the measurement and adjustment.

• Rms of primary less than 1.6  mm over the beam area.
• Image of radial errors after 1st round of adjustments (.gif)
• Errors along each north/south set of targets (.pdf)
• median and rms Errors for each north/south set of targets (.pdf)
• top is median, bottom is rms
• Red are targets above north/south support cables, red are in between