Photogrammetry – Aerial Photography and Procedure in Surveying

Photogrammetry, often known as aerial photography, is a type of surveying that involves combining a number of images taken in a given area to create maps such as planimetric or topographic maps. There are two types of photogrammetry: Photogrammetry on the ground Photogrammetry from the air Images are taken from a fixed place on the ground in terrestrial photogrammetry, while aerial photogrammetry uses a camera equipment to capture photographs from the air while flying over the ground. We’ll talk about aerial photography in this article. The following are some of the words or meanings used in aerial photography: Station of Exposure An exposure station is a point in space where an aircraft is positioned with a camera for a single exposure by the camera lens. Flying Altitude The exposure station’s height above the datum is.

Points that are homologous

Homologous points are a collection of points that demonstrate both ground and photo points. This happened when the original plane and the projected plane collided. Aerial Photography Techniques Putting in place control points Planned flights and photographs Stereoscopy and photo interpretation Parallax and parallax measurement Cartography and map construction Control Points Establishment Control points are fixed places on the ground that have known relative positions. Setting these control points as boundaries allows the shot to be observed. As a result, the points should be set up in such a way that they are clearly identifiable in photographs. In one shot, a minimum of 3 to 4 control points are required. The location of control points is determined by the map’s scale, flying control, and cartographic information.

Photography and flight Planning entails determining the flight’s height while taking images, the area to be covered in each photograph, the number of photographs, the number of strips, and the time interval between b/n exposures. The following considerations play a major role in this planning.To be surveyed area Overlap in camera focal length Photographic Scale Ground Aircraft speed in still air There are several equations available for various parameters, as shown below. Aircraft Elevation It can be calculated using H = contour interval x C = flying height Where C is a number between 500 and 1500. One photograph covers a large area.(length x scale) x (area covered by one photograph) (width x scale).

Stereoscopy and photo interpretation

The stereoscope, which is equipped with magnifiers, is used to interpret photographs. As a result, one can see a three-dimensional model of the area via it, and it also makes producing maps of the photographed area easier. Control stations, altitudes, and line lengths should all be provided in sufficient quantities for accuracy. As a result, we may argue that picture interpretation will allow us to understand the importance of items in a photograph. When it comes to stereo scopes, there are four different types that can be utilised for photo interpretation. They are, in particular Stereoscope lens Stereoscope with mirrors Stereoscope with a scanning mirror Stereoscope with zoom Stereoscopy and photo interpretation Photo interpretation is primarily done with lens and mirror stereo scopes. Aside from this, there are a few features that should be maintained for proper photo interpretation. The following characteristics should be present.

The shape of an object in a photograph is quite essential. The shape of an object is determined by its outline or configuration. As a result, an abject in a map or photograph can be clearly identified by its shape.SizeIn picture interpretation, the size of the image is equally essential. The size should be set to a scale and interpreted correctly on the photograph. The only person who can tell the difference between large and little objects is the observer. The size of a big river or drain, for example, should be understood in different sizes. Pattern The objects in the shot should be arranged in a logical pattern that allows them to be clearly identified without any overlapping confusion. Shadow When looking at things from the top, it’s easy to get confused.

Parallax and Parallax Measurement

The term “site” refers to the physical position of an object. Based on its surroundings, an object’s location can be easily determined. An aerial image can be used to determine the position of an object based on its co-ordinates. Similarly, to determine the third dimension of the same item, at least two points of observation from different angles are required. When the point of observation is adjusted to a different angle, parallax causes an object in the shot to move. The following are two methods for measuring parallax in general: Parallax bar with floating marks Parallax and Parallax Measurement Map and cartography construction After you’ve gathered all of your photos, it’s time to make or edit them.

Method of the Radial Line The graphical approach of plotting the map using vertical images is known as the radial line method. We may create a planimetric map using this way. This approach makes use of some form of perspective attributes. That is, in the snapshot, a central point is fixed, and the items near this point are free of tilt errors. The shift in an object’s location caused by tilt and ground relief is measured from the principal point outwards. The intersection of three rays from known points can be used to correct the location of a point in two overlapping photos. Method of the Radial Line Method Using a Slotted Template Plotting with a slotted template is a mechanical process. Templates, which are nothing more than larger photographs of the target, are created using this procedure.

Method of stereoscopic observation

For the preparation of maps in the stereoscopic plotting method, a device known as a stereo plotter or multiplex is employed. The maps created using this technology are extremely precise. The gadget will assist in viewing the overlapping region in three dimensions, which will aid in viewing the spatial model. The model is then measured and projected orthographically as a map. Large mapping firms utilise this method because it is more accurate.

Photogrammetric surveying, often known as photogrammetry, is a discipline of surveying that involves creating maps from photographs obtained from ground or air stations. With the advent of photogrammetric techniques, pictures are now being utilised for geological interpretation, soil and crop classification, and other purposes. Is the science of taking measurements from photos, particularly to retrieve the precise positions of surface points. Especially for reconstructing the exact placements of surface points, Er.Pramesh Hada, Asst. Professor,nec Used to reconstruct the motion paths of given reference points on any moving object, its components, and the immediate surroundings. To detect, measure, and record complicated 2-D and 3-D motion fields, photogrammetry can use high-speed imagery and remote sensing. Er.Pramesh Hada,Asst. Professor,nec.

Broadly Photogrammetry Requires

Satellite tracking of relative location variations in all Earth conditions is one of its applications (e.g. tectonic motions etc.), The quantitative results of photogrammetry are used to guide and match the results of computational models of natural systems, assisting in the invalidation or confirmation of new theories, the design of novel vehicles or new methods for predicting or/and controlling the consequences of earthquakes, tsunamis, or any other weather types. Triangulation, trilateration, and multidimensional scaling can all be solved with photogrammetry. In the most basic case, the distance between two points on a plane parallel to the photographic image plane can be calculated by measuring their distance on the picture, assuming the scale (s) of the image is correct.

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