Loading...
Please wait, while we are loading the content...
Similar Documents
Image Geometry of Vertical & Oblique Panoramic Photography
| Content Provider | Semantic Scholar |
|---|---|
| Copyright Year | 2008 |
| Abstract | This is the last of three articles on image motion in aerial photography. Thejint one, in the January 1965 issue, was a mathematical analysis of the image motion compensation and the image motion from the aircraft's forward movemen t for the oblique frame camera. The second article, in the Septemberissue, analyzed the image motionfrom random rotational motions of the aircraft for the frame and panoramic cameras. To complete the series of studies, the image movement from the aircraft's velocity for vertical and oblique panoramic cameras is investigated here. A brief description of the panoramic camera includes the distortions associated with it. Several equations of interest pertain to the panoramic cameras, such as the coordinate transformation and image velocity equations, from which the proper image motion compensation velocity, residual image motion, and the image displacements are derived. A n easy method of rapid location of ground points from the panoramic photograph can be applied. lence. The random motions of the aircraft generally are not a problem except at high altitudes where high resolution is necessary. A stabilized mount may be included to damp out the motions. At very low altitudes fast shutter speeds minimize the effect of the larger pitch and roll motions. The effect of random or rotational motions was examined in Reference 6, but the equations for the image motion on the vertical panoramic photograph are repeated later in this article. For vertical panoramic photography the effect of the forward velocity is greatly reduced by imparting a movement to the lens or film (image motion compensation). The proper velocity of this movement is determined by a measuremen t of the angular velocity of the object space, obtained from a velocity-to-height sensor. The required velocity varies \\·ith the cosine of the lateral viewing angle. If the sensor and the image causes distortion in the photograph because of the focal plane shutter. The primary distortion in panoramic photography from the true pictlu'e of the ground is, of course, the panoramic distortion caused by the curvature of the film. The shutter introduces two additional image displacements, These displacements arise from the movement of the aircraft as the shu tter sweeps across the ftlm and the changing position of the lens relative to the film for image motion compensation. The first is known as the sweep posi tional displacement and the second, the IMC displacement. Both are depicted in Figure 4. A detailed description of the sweep positional and IMC displacements was included in Reference 5 as the displacements apply to oblique frame photography. It is sufficient to state here that the two displacements do not cancel each other, and there is a residual displacemen t. However, these displacemen ts are IMAGE GEOMETRY OF VERTICAL & OBLIQUE PANORAMIC PHOTOGRAPHY 301 FIG. 4. Displacement of center line due to the sweep positional 'l.nd 1Me distortions. known and are, therefore, recoverable. For the oblique orientations the tilt of the camera produces another distortion. These distortions prevent rapid photointerpretation without special equipment. However, there are methods of overcoming this obstacle. One such technique involves a transparent grid overlay which allows the rapid location of image points appearing on the panoramic photograph. This techniq ue is described in more detail later. DESCRIPTION OF THE EQUATIONS AND METHOD OF DERIVATION Equa tions for several parameters of interest are given in this article, as they apply to vertical and forward oblique panoramic photography. These are: Transformation equations from photo to ground coordinates. The velocity of the image from the forward movement of the aircraft. The velocity of image motion compensation. The residual image velocity. The image velocity from rotational motions of the aircraft. The sweep positional displacement. The image motion compensation displacement. The equations for the IMC velocity, the residual velocity, and the sweep positional and IMC displacements are derived from the equation for the image velocity from aircraft movement. The derivation of the latter equation is straightforward for the vertical panoramic, but for the forward oblique orientation the derivation becomes complicated. The actual derivation is given in another article by the author. 3 It consists of resolving the velocity of the ground point into three mutually perpendicular componen ts, one along the line-of-sight which does not contribute to the image velocity and the others in directions parallel to the x and y-directions of the photograph, and mul tiplying these components by the appropriate scale factors. This procedure is valid because one component contributes only to the velocity in the xdirection and the other to the y-direction. The formulas for the sweep positional and IMC displacement are derived by integrating the image velocity with respect to time, where time is measured from the moment at which the nadir point is exposed. The difference in the integrations for the two displacements arises in the treatment of the sweep angle; for the sweep positional displacement this angle is treated as a constant and for the IMC displacement it is made a function of time. The reason is that the velocity of an image point depends only upon the sweep angle of the image point, which is a constant, but the veloci ty of the lens varies wi th the sweep angle of the lens. The transformation equations for the oblique camera are derived by treating the panoramic photograph as a series of infinitesimally narrow frame photographs, each at a slightly different roll angle. Then the appropriate substitutions are made in the transformation equations for a tilted frame camera,4 with the definitions of the pitch and roll found in paragraph (a) of Ref. 5. The residual velocity is simply the difference between the velocity of the image and the velocity of the film or lens for image motion compensation. It does not take into accou nt the inaccuracies of the 1M C dri ve and the velocity-to-height sensor. However, 302 PHOTOGRAMMETRIC ENGINEERING Lly'lwp = LlYimc = 0 VJ . .6.:rimc = -----:-Sin fJ lin 4. Sweep positional and IJ1!{C displacements. |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.asprs.org/wp-content/uploads/pers/1966journal/mar/1966_mar_298-306.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
