By extension, we could have a large block of aerial photographs, overlapping in the direction of flight as well as between adjacent flight lines, all oriented relatively to each other. Voila! When adjacent photos are viewed through a stereoscope, the difference in perspective allows the viewer to see the image in three dimensions, or stereo. You'll now have to try to picture this demonstration as I describe it in words. The resulting imagery had a ground resolution of 60 cm (2 ft). Picture the bundle of countless rays of light that make up a single aerial photograph or digital frame image at the instant of exposure. These are the years of aerial coverage that we currently have for the area indicated by center point of the map. We now have two bundles of light rays, some of them intersecting in the middle of my desktop. If the target surface is perfectly flat, then the elevations of the three known points determine a mathematical plane representing the entire surface. The distance in the air between the two flight lines (W) is called lines spacing. I can't move the photograph around as much as I could with only one piece of string attached, but the photograph can still be rolled and twisted with respect to the desktop. Now we can precisely locate any point on the desktop surface, regardless of its shape, in 3-dimensional space. = 1,000 ft (or 1”=1,000’). In fact, with 60% forward overlap, every point in a single flight line is seen 3 times. Aerial photography coverage is only for selected areas in Washington State, with an emphasis on the Puget Sound region, in a variety of scales, from 1944 to the present.Digital orthophotography available on the Geospatial Data Resources Guide (formerly WAGDA) website (1990's- present) supplements our paper collection.. Let's return to the example I described above. Oblique aerial photos show buildings, infrastructure, and land from all sides.As a result, you see more natural three-dimensional perspective v… This line connects the image centres of the vertical photographs. For any given point common to both photographs, we now know the exact length of each of the two pieces of string (one from each photograph) that connect to the imaged point on the ground. Today, we can actually measure position and angular orientation of the camera with respect to the ground with GPS/IMU direct georeferencing technology. Selected print satellite images show entire countries, … 8.3 Small scale: Smaller-scale photos (e.g. With that single piece of string, I cannot precisely locate or fix the position of the camera focal point or the orientation of the camera focal plane as it was when the photograph was taken. A small scale photo simply means that ground features are at a smaller, less detailed size. 6.3 PHOTO OVERLAP Aerial photo projects for all mapping and most image analyses require that a series of exposures be made along each of the multiple flight lines. The Pennsylvania State University © 2020, Source: Elements of Photogrammetry with application in GIS, 4th edition, 2014 McGraw Hill, Source: Elements of Photogrammetry with application in GIS, 4th edition, 2014 McGraw HillÂ, Geospatial Applications of Unmanned Aerial Systems (UAS), Lesson 1: Introduction to the Unmanned Aerial System, Lesson 4: UAS Mission Planning and Control, Lesson 6: Aviation Regulatory and Certificate of Authorization (COA) Process, Lesson 10: UAS Safety and Privacy Concerns, Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, Department of Energy and Mineral Engineering, Department of Materials Science and Engineering, Department of Meteorology and Atmospheric Science, Earth and Environmental Systems Institute, iMPS in Renewable Energy and Sustainability Policy Program Office, BA in Energy and Sustainability Policy Program Office, 2217 Earth and Engineering Sciences Building, University Park, Pennsylvania 16802, true vertical photography: ±0º from nadir, tilted or near-vertical photography > 0º but less than ±3º – Most used –, oblique photography: between ±35º degree and ±55º off nadir, Chapter 18 of Elements of Photogrammetry with Applications in GIS, 4th edition. The photograph captured is observed by setting these control points as boundaries. Your readings will take you into greater depth and detail, but I hope my explanation helps you create a 3-dimensional picture in your mind, making the readings easier to understand. In photogrammetry, we call this a space intersection. The site editor may also be contacted with questions or comments about this Open Educational Resource. Here is what I have for when the camera is pointed straight down (Note: this gives me the length of each side of ground coverage. However, because of the light weight of the UAS, we expect substantial air dynamic and therefore substantial rotations of the camera (i.e. Distance B is also called air base. It takes a more rigorous education to make quantitative statements about the spatial accuracy of those products. The length of each ray, from the focal point of the camera to the imaged point on the ground, is determined by the height of the camera lens above the ground and the elevation of that point on the ground. In Figure 4.4, the distance on the ground AB will be projected on the image on line ab, therefore, the image scale can be computed using the following formula: Equation 1: scale =  distance ab distance AB. Understanding errors and the potential consequences of error is a very important part of the decision-making process. Sentinel-2 is the start of a new and exciting era… In order to understand mission flight planning, you need to understand the geometry of the image as it is formed within the camera. Side lap is a term used in photogrammetry to describe the amount of overlap between images from adjacent flight lines (see Figure 4.6). One image is taken from over the left side of my desk, and the other is taken from over the right side of my desk. This time, imagine I have two photographs of my desktop taken from two separate vantage points, and that the individual images actually overlap. The length of each ray, from the focal point of the camera to the imaged point on the ground, is determined by the height of the camera lens above the ground and the elevation of that point on the ground. Images from each camera have the same ground resolution, but the images from the Lt1245R are four times as large. This overlapping area, although of the same portion of ground, has been photographed from two different angles, providing two different perspectives of that portion of ground. This geometric relationship between the image and the ground is called exterior orientation. Aerial photographs are acquired by aircraft equipped with mapping cameras. As I mentioned earlier, the mathematical equations of photogrammetry allow us to quantify this uncertainty in statistical terms. 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