Orthophotography?

<p>I'm a commercial photographer looking to find out what goes into Orthophotography. That is creating accurate aerial map images.<br>

I just found a company looking for bids on an upcoming project, and I'm wondering if this is something I should be interested in, or if it's so specialized that I should let it pass. The project requires images of a 4 square mile area. The deliverables include: flight plan map containing: flight lines, flight breaks and proposed ground control, a camera calibration report, aero-triangulation data in any standard format, and a set of color orthophotos in GeoTIFF & Mr. SID formats.<br>

I've taken photos from a helicopter before using a gyro, but never for mapping purposes. Are these images usually done with a camera mounted to t he plane? Who takes these photos, normal photographers or people who specialize in this type of work?<br>

Thank you.</p>

<p>It sounds to me that the request for tender calls for specialized work for GIS-type accuracy. I think they'll be looking for professional certification.</p>

<p>Geospatial services is indeed highly specialized by companies such as:<br>

<a href="http://www.aerometric-mn.com/index.html">http://www.aerometric-mn.com/index.html </a></p>

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<p>I used to work as an instrument operator. My gut instinct is to tell you that you are about to get in over your head. Watch your step. </p>

<p>An old land survey text recommends the book, "Airphoto Interpretation of the Physical Environment" by G. Bird and I. Hale. This would be for applying the information from an aerial photo.</p>

<p>First off, if you don't know anything about how a survey crew or an engineer uses aerial photos, you need to sit down and talk to someone at a firm. </p>

<p>The basic answer is,<strong> equipment considerations alone</strong> make photomapping (photogrammetric mapping) a specialized job. We're talking about lens assemblies that look like they are about the size of a basketball, in housings that look like they ought to be bombardier sights on a WWII era plane. </p>

<p>The math is very important. Scaling problems are the mainstay. People who are into mapping have to switch, in their imaginations, between several different mathematical models of how the earth is represented. The guy who's doing the aerial photo maps needs to understand those models, and still fly the plane in a snaking path. This path will be flown so that the photos overlap at a constant, established rate, not only between the first and next in a line, but also among adjacent lines. </p>

<p>Scaling. Let's cover that again. Scaling. </p>

<p>Ground control. Usually what we would use would be GPS'd points; done in rapid static survey; you're looking for controls that are done to a millimeter or below. Good news if the flyover area includes an airport (it rarely does). Airports are common sites for well documented A and AA class surveys; this means that the recorded data on those will be within very fine tolerances. Airports are a great place to start a survey traverse. And also a big headache for being on some of those runways. If you're into planes, I take it you are familiar with those ideas. </p>

<p>Normal photographers could do it if they wanted; you don't have to be superman, but you'd have to do the math. Truth is, nobody wants to do the math. They might be willing to hang a DSLR out of an open door of a small aircraft, but that's not the same as this stuff. </p>

<p>You need to conference with a PLS or PE. You need a guy who has his "stamp." </p>

<p>As soon as I see that line about proposed ground control, what that means, of course, is a large white arrow pointing to a GPS survey monument. These arrows are often in the shape of a V with the monument in the inside crotch of the V. Sometimes you see these nailed down (white fabric V) on the side of the highway; highways also often have well recorded bench monuments. </p>

<p>I never heard of the GeoTiff or Mr. SID; that must be new; I have only used Leica mathematical modeling equipment. The engineers will be the one who primarily do the computer mapping; the survey crews will do the information gathering and the measuring; there is a legal separation between surveyors, engineers and architects that forms three layers of safety for the public. Surveyors do the measuring. </p>

<p>What you are proposing is to measure a very large area, in a very disciplined way, from a moving vehicle with three dimensions of variation in its course. You can't fly by the seat of your pants for this one. </p>

<p>If these terms are far off for you, I would recommend some serious reading and a good gut check to make sure you are not about to get yourself in too far. I ran across one or two surveys every few months which had been taken up by other crews and abandoned when they realized what was up. A couple of those must have been profit margin tragedies for somebody.</p>

<p>If you really thought an ordinary photographer did this, like with a DSLR, you are about to mess up. Talk to a PE and a PLS and see what's up. It's not impossible for you to do this, but I suspect you need some field time and some book learnin'. </p>

<p>FWIW, every photogrammetric survey I ever saw was very good. Unfortunately, for all that work, they have a limit to their usefulness. It's obvious to anyone who reviews the photos, they were made with a strict adherence to an established plan for that flight. If you make an error, everyone will notice; maybe before they look through the loupe. </p>

<p>You can't cover up a flub with photoshop on this one. An <strong>exceptional, thorough, understanding</strong> of Trigonometry is an <strong>important part</strong> of any survey crewman's knowledge base. This includes the plane fliers. </p>

<p>Really, even not knowing you, and nothing about you, but asking the question alone would inspire me to tell you to try to get out of this. If you didn't understand those terms and what was proposed from working a survey somewhere before, there's a big headache and maybe some trouble for you ahead. </p>

<p>Vertical surveys of any kind (mine, skyscraper, aerial, underwater) are all a real bear. Making a ray into a line segment sounds easy, and then you have to do it with one of these, and then scale. Super easy in elementary school; enough to unleash rage and tears and frustration in the middle of one of these math problems. Hang on for that. </p>

<p>Really, learn up. If you haven't done surveys before, I caution you. Surveys have to be done right. </p>

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<p>I'll tell you this, though, those cautions aside: surveying is a great profession for people interested in physical and intellectual adventure. Combine it with photography and flying, and be good at it, you'd be set. </p>

<p>I wish I had learned about what surveying was really like before I started college. I would have definitely committed to a serious engineering program and studied civil or just gone for Land Survey. It's a good profession which involves some strong thinking. </p>

<p>Surveying can be a great physical and intellectual adventure. There will be many challenges in the store for you if you choose to pursue this. Good luck. </p>