👉🏼👉🏼 So You Want to Create Maps Using Drones? https://amzn.to/3aW197j
👉🏼👉🏼 Drones for Conservation https://amzn.to/3dW4DJf

After reading extensively on this subject, I decided to contact Chris McGlone, editor-in-chief of two editions of the Manual of Photogrammetry, published by ASPRS. He holds a Ph.D. in photogrammetry from Purdue University. He has worked on the development of photogrammetric instruments and computer vision for cartographic feature extraction, and visual simulation. Since he is also the co-author of the textbook “Introduction to Modern Photogrammetry,” I thought he could help us navigate through these stages. Each stage represents different technological approaches to the fundamental problem of determining positions from imagery.

Plane table photogrammetry : A plane table is a flat board on a tripod that holds a map. The operator sighted through a telescope on a protractor and recorded the distance and angles to various objects. A camera set to take the place of the telescope, recording the angles to all of the objects in the scene. Photogrammetry at this point was done graphically, either using plane table photographs or photographs taken from known positions and orientations.

Analog Photogrammetry: Analog instruments were developed to perform the intersection calculations by mechanically reproducing the geometry of the image. A number of variations were developed. In one case, the lens was modeled by a ball joint and the light rays through the lens by metal rods. The operator viewed the scene in stereo through the optics and a small dot was superimposed on each image. The operator could place the floating mark on the ground by changing its position relative to the images and thereby trace contours or measure elevations.

Analytical photogrammetry refers to solving the image ray projection numerically, instead of by analog computation. Coordinates of points of interest were measured on the images using comparators. The position/orientation of the images and the positions of the points were calculated using the collinearity equations, which state that the perspective center, the image point, and the object point all lie on a straight line.

Digital photogrammetry , as the name suggests, deals with digital imagery. As with analytical photogrammetry, position calculations are done mathematically. Special-purpose stereoplotting equipment is no longer needed. A computer workstation with good image display capacity is sufficient, if equipped with a stereo viewing capability . The use of digital imagery enables the automation of tasks such as elevation extraction and operator assistance in other tasks, such as control point measurement. Products are increasingly image based, with the most common product now the orthoimage, which is an image with elevation effects removed such that it can be used like a map. Orthomosaics, formed by combining orthoimages, are commonly used as base maps for GIS systems and as the basis for topographic maps. Other common products now include 3D models of terrain and buildings.