After I returned from Puerto Rico in 1974...

I was looking for something like my friends Roger or Chris had, a humble job in a technical area where I could combine my academic training with real industrial experience, I was willing to work up from the shop floor. I already knew I wasn't Nobel prize material, but I wanted to learn how to do something. Now was the time to learn a trade.

It did not go as quickly as I expected, it wasn't until about three or four months after I had returned to Florida that I found the job I was looking for, a trainee cartographer for an air photo mapping firm in Lakeland, about 30 miles east of Tampa; right off the Interstate, I could get there in half an hour from my apartment in town. I knew back then that the world was running out of resources, and that managing our diminishing supply efficiently would be important, hence profitable, work. I wanted a good job, I wanted prestige and money and interesting work, but I also wanted to do something useful to others. This was the seventies, remember? The work I was learning was highly skilled labor, and it required about a six months apprenticeship before I could be productive, and it would be two years before I could work without supervision, I jumped for it, even though I started off at minimum wage. My title was 'compiler' or 'stereo plotter operator', that referred to the mapping machine I was going to be working with. The technology was called photogrammetry, and although it was new to me, it had been more or less perfected by the end of the war, bear with me while I explain.

An aircraft flies over a piece of ground steadily photographing the earth with a very precise and enormous camera (the individual frames are 9x9 inches) in such a way that the images on the negatives overlap about 60%. This means that every point on the ground is imaged on at least two, and sometimes three, of the exposures. After the plane flies down a long flight line, it turns around and flies back in such a way that the exposures on this new flight line 'sidelap' the previous line. This process is repeated until the entire plot of ground to be mapped is completely photographed, and every spot on the ground appears on at least two subsequent pictures. This is where the stereo part comes in, if you look at the overlap section of two photos, and if each eye focuses on one of them, you can see the ground in stereo, in three dimensions! You can actually see trees and buildings poking up towards you, and every dip and hump on the ground is clearly defined, in depth. It's the same principle as those silly three dimensional movies, where you have to wear special glasses to get the effect. Think about an everyday activity that demands depth perception, say, threading a needle. In this case, your eyes actually cross to focus on the same spot, the eye of the needle, and your brain determines, from the amount of crossing, exactly how far away the needle and thread are so you can bring them together. You use the same method to fool the eye in stereo photogrammetry, except that you are looking at two separate photographs and your eyes have to cross to fuse the images together. It's as if the distance between the two points where the images were exposed was the actual separation between your two eyeballs, hundreds of feet, and if everything is aligned up properly the effect is striking, and as it turns out, extremely precise; accurate elevation measurements can be made from thousands of feet up in the air.

In practice, the process is a bit more involved. First, the film rolls are processed, and the individual negatives are printed onto glass plates painted with film emulsion. After they are developed and dried, the plates are clamped down onto holders mounted on a metal frame, each one being capable of being tipped, tilted, and swung independently. The two plate holders, or 'buckets', also slide back and forth so the distance between the two can be adjusted. With this arrangement you can exactly duplicate the geometrical relationship of the film planes in the original photography back at the lab, at a reduced scale. Two colored lamps, usually red and blue, shine through each plate and focus on a small stage free to roll around on a table positioned under the frame. Each lamp casts an image of its own plate on a small white surface mounted on the stage, so that you are looking at two images simultaneously, a red view of one plate and a blue view of the other. To see the effect, the operator must wear a pair of glasses with a blue lens over one eye and a red lens over the other. Each eye sees a different photo, the eyes cross to fuse the two together, and the operator gets the illusion of looking through a magic hole floating in the dark in front of him, with a perfect black and white picture of the ground, as seen from a great height in 3-D, visible through it. A tiny hole is drilled in the center of the stage and a speck of light is visible through it, by raising and lowering the stage (with a knob) the optical illusion is created that a little dot of light is being raised and lowered by the operator, and he can drop it precisely on the ground surface and read the elevation off a counter.

The long training period was necessary because not everyone can see in stereo, and even those who can have to train their eyes to do it with sufficient precision. The other problem is that the photographs are taken from a light plane bouncing around in strong crosswinds, and it takes a long and involved procedure of alternatively tipping, tilting and swinging the plate holders until the aircraft attitude error is removed from the photos and the two images fuse into a 'model'. A model is that imaginary space formed by the overlap of the two plates after the individual photos are manipulated to remove the aircraft's yaw, pitch, and roll. And it's not over yet, once the model is established, the entire model itself has to be rocked back and forth and left and right (using big threaded screws that tip and tilt the entire frame the buckets ride on) until the model matches the elevation of the ground. The buckets can be slid towards or away from each other to alter the scale. Scale and elevation are determined by locating known points visible in the model of established position and height above sea level (from a ground survey conducted earlier). You've no doubt seen these 'aerial targets' while riding around, usually big "X's" painted at road intersections. Surveyors set up their instruments on these landmarks and establish their elevation and position, and this information allows the photogrammetrist to calibrate his model. When the job is done, every point on the model can be located to a high positional accuracy and its elevation determined precisely. The stage also has a pen mounted directly under it as well, so the operator can trace buildings, roads, and contour lines. It takes a good operator about twenty minutes to go through this set-up procedure, and it takes him about a year to learn how. Depending on the nature of the terrain and the amount of detail to be mapped, an individual model can take from about half an hour to several days to complete. Most jobs consist of many models, and sometimes many flight lines, and all the edges have to match up. Invariably problems arise, targets are covered up or lost in shadow, or surveyors make mistakes, or the pilot can't quite control his aircraft to specs, so there's a lot of fudge work to be done as well. When you finally master the technique, then comes the art, seeing the ground level through the trees, learning to ignore false elevation cues caused by wind blowing vegetation around between photos (remember, the theory expects everything on the ground to not move between pictures) and reading featureless ground like snow or tall grass.

I have described only the simplest plotter I worked on, because it is the easiest to explain, but the more sophisticated models I used could be much more complex and accurate. The principle remains the same, and even the simplest plotters are capable of phenomenal accuracy (less than a foot of error in elevation from several thousand feet up). Photogrammetry is accurate enough to be used for engineering maps, stockpile inventories, and support of strip mining operations. One of our biggest clients were the phosphate mines, who were constantly trying to figure out how to move big piles of dirt around as cheaply as possible. I found the work fascinating in principle, even if a bit tedious in practice. I also got a chance to work with real craftsmen, from the old timer who taught me my craft to the wizards that worked in the photo lab, and the master photographer behind the camera. I gained a real measure of respect for the pilots as well, who have to fly over featureless terrain they can't see, bucking crosswinds and turbulence while transferring the rigid geometry of the flight lines to the ground below. I got a chance to do all of these things, but map compilation was the only thing I was given the opportunity to get good at. Compilers are harder to get than pilots. I also was overwhelmed by the character of the men I worked with, not just their skill, but their integrity. These men would not tolerate sloppy work, and they would not do a half-assed job; they gave their all for the client. The management, on the other hand, was...well, typical management. Some things never change.