Aircraft navigation aids

[holograph]

In another thread, there was some discussion about aircraft navigation beacons. Although this is not a beacon, I thought some of you might be interested to see one of the early (1939) aircraft navigational aids. The image below is a "cross-eyed" stereogram of the center of Scranton, Pennsylvania, on June 4, 1939. The images were aerial photos taken for the Agricultural Adjustment Administration and which were digitized and put online at the PennPilot web site.

 

The top of the large tank has been painted with an arrow pointing to the nearest airfield. A pilot, flying visually, would see these signs and be able to find the airfield. I've seen such signs painted on top of barns, too.

 

If you are not familiar with "cross-eyed stereograms", you need to cross your eyes slightly when viewing the image to see the stereo effect. No special glasses required, but it may take a little practice to see it. If you have trouble, try holding a finger near your face, focus on your finger, and move it toward the image until you see the stereo image converge.

 

[Wintertime]

dadgum, I haven't done one of these in a long time, and my brain is insisting on reversing the levels so that the water tower appears to be a well, and the houses are all sunken alongside the elevated streets! Anyone got a tip for popping into 3D the right way?

 

Patty

[68-eldo]

dadgum, I haven't done one of these in a long time, and my brain is insisting on reversing the levels so that the water tower appears to be a well, and the houses are all sunken alongside the elevated streets! Anyone got a tip for popping into 3D the right way?

 

Patty

 

Try putting blinders on. Looking at the photo put a hand or something else to use as a blinder so that the left eye can not see the left image but can see the right one. Then put a blinder over the right eye so it can not see the right photo but can see the left one.

 

Then view the image with slightly crossed eyes. It should soon pop out at you. It is pretty amazing.

 

Glen

Edited September 21, 2011 by 68-eldo

[holograph]

dadgum, I haven't done one of these in a long time, and my brain is insisting on reversing the levels so that the water tower appears to be a well, and the houses are all sunken alongside the elevated streets! Anyone got a tip for popping into 3D the right way?

 

Patty

You may have wide set eyes, or a relatively small screen, because if you see inverted relief, it means that you are focusing behind the image so that your left eye is seeing the left image and the right eye is seeing the right image. It only works if you can focus in front of the image so that the left eye sees the right image, and the right eye sees the left image. The finger trick is supposed to help you focus in front of the image. Sitting further from the screen may help, if you normally sit close to the screen.

[mloser]

I swear I saw a similar arrow on top of the Hamilton Watch Company building in Lancaster, PA but I can't locate it now, or even WHY I was looking at an aerial photo of the building (I know it had something to do with a survey mark, and was probably something I picked up reading an old NGS report from Google Books). The arrow was clearly painted on the roof of the building and pointed, if memory serves, to the Lancaster airport, a few miles to the north (NNE to be more specific). I thought it was on PennPilot but a search of pics on that site didn't show it.

[AZcachemeister]

Got a couple of similar items around here, sorry...no stereograms.

 

N33° 29.519 W111° 37.755

 

N34° 25.092 W111° 24.518