counter hit xanga

Unlike Aerial Photography, Landsat Imagery Is Interpreted Through Techniques Collectively Called?

by -44 views

🕑 Reading time:

i infinitesimal

Photogrammetry or aerial photography is the co-operative of surveying that deals with production of maps such as planimetric or topographic maps by compiling number of photographs taken in that surface area. Photogrammetry consists two branches:

  1. Terrestrial photogrammetry
  2. Aeriform photogrammetry

In terrestrial photogrammetry photographs are taken from a fixed position on ground while in the aerial photogrammetry, an shipping with camera setup is used to take photographs from the air flying over the ground. In this article nosotros volition hash out about the aeriform photography.
Photogrammetry - Aerial Photography

Contents:

  • Terms Used in Aerial Photography
    • Exposure Station
    • Flying Height
    • Altitude
    • Tilt
    • Swing
    • Principal Indicate
    • Isocenter
    • Nadir point
    • Homologous Points
  • Process of Aerial Photography
    • Establishing Command Points
    • Flying Planning and Photography
    • Photograph Estimation and Stereoscopy
    • Parallax and Measurement of Parallax
    • Construction of Map and Cartography


Terms Used in Aerial Photography

The terms or definitions used in aerial photography are:


Exposure Station

An exposure station is the betoken at which aircraft is positioned in infinite with camera for instant of exposure by camera lens.


Flying Height

The elevation of exposure station higher up datum is called as flying height.


Altitude

Altitude is the vertical distance between the shipping and earth’s surface or ground.


Tilt

Tilt is an angle produced by the rotation of aeriform camera most line of flight (vertical axis).


Swing

Swing is bending produced past the rotation of aerial camera about horizontal axis which is perpendicular to the line of flying. Swing is also chosen as tip.


Primary Indicate

When aerial photographic camera captures a photograph of ground, the optical axis of camera will intersect at some betoken (centre) in the aerial photograph. This point of intersection is called equally primary aeroplane.


Isocenter

Bisector of bending of tilt will intersect somewhere on the photograph (at a altitude of f tan (t/2)). This point is known as isocenter.


Nadir point

Nadir betoken is a bespeak on an aeriform photograph pierced by the plumb line when dropped from front nodal point.


Homologous Points

The combination of points demonstrating basis points and photograph points are known as homologous points. This combination happened between original plane and projecting plane.


Procedure of Aerial Photography

  • Establishing control points
  • Flight planning and photography
  • Photograph estimation and stereoscopy
  • Parallax and measurement of parallax
  • Construction of map and cartography


Establishing Command Points


Control points are points established on footing with known relative positions. The photograph captured is observed by setting these command points as boundaries. And so, the points should exist established in such a style that they should be hands identifiable on photograph. There should be minimum of 3 to 4 control points are need in one photograph. The establishment of command points depends upon the scale of map, flight control, and cartographical method of mapping.
Establishing Control Points in Photography


Flight Planning and Photography

Flight planning is nothing but knowing the elevation to be maintained by flight while taking photos, expanse to exist covered in each photograph, number of photographs, no of strips, and time interval b/n exposures. This planning mainly depends upon the following factors

  • Area to be surveyed
  • Focal length of photographic camera
  • Overlap
  • Calibration of photo
  • Ground Speed of aircraft in still air

There are some formulae are available for different parameters as follows.
Altitude of Aircraft


It tin be computed from Flying acme H = contour interval x C Where C varies from 500 – 1500
Area covered by one photograph

Expanse covered past one photograph = (length x scale) ten (width x scale)
Number of photographs required

No. of photographs required to cover all the given area are = N1 10 N2 Where N1 =Li/((1-P50)Sl
) + 1 & N2 = B1/((1-Pw)Due southw) + 1 Where N1 = number of photographs in each strip N2 = number of strips L1 = length of photograph (in direction of flight) L2 = width of photograph (perpendicular to the direction of flight) Pl
= longitudinal overlap Pdue west
= Side overlap Southwardl
= scale in length wise Sw
= calibration in width wise
Flight Planning and Photography


Photograph Interpretation and Stereoscopy

Photo estimation is done past the instrument called stereoscope which contains magnifiers. So, one can observe the three-dimensional model of area through it and it also ease the cartoon of maps of photographed area. For accuracy, control stations, elevations, length of lines should be sufficiently available. So, nosotros tin can say photo interpretation will enable the significance of objects in photo. Coming to stereoscopes, at that place are iv types of stereoscopes are available which are used for the photo interpretation. They are namely

  • Lens stereoscope
  • Mirror stereoscope
  • Scanning mirror stereoscope
  • Zoom stereoscope

Photo Interpretation and Stereoscopy
Lens and mirror stereoscopes are majorly used for photointerpretation. Apart from these, some characteristics should exist maintained for skilful photo interpretation. The characteristics should exist as follows.

  • Shape
  • Size
  • Blueprint
  • Shadow
  • Texture
  • Site

Shape

Shape is an important property for an object in photograph. The outline or configuration will deliver the shape of an object. Then, one tin can easily recognize from the shape of an abject in the map or photo.

Size

Size is also an important factor in photo estimation. The size should fixed to some scale and properly interpreted on the photograph. And then only the observer tin feel the difference between large objects and small objects. For instance size of major river and drain should be interpreted in unlike sizes.

Design

The system of objects in the photo should be done in a skillful pattern in such a manner that they should be easily recognizable without any overlapping confusion.

Shadow

Sometimes height view may create defoliation about object type, shadows of that type of objects will help to detect the profile of an object.

Texture

Texture of an object in the photo is produced by the whole combination of its shape, size, shadow, tone etc. so, it is dependent of scale of photograph and considered mainly in large scale photographs.

Site

Site is nothing but location of an object. The location of an object can be easily identified based on its surroundings.


Parallax and Measurement of Parallax

An aerial photograph tin be studied to become the location of an object past its co-ordinates in the photo. Similarly, to know the third dimension of aforementioned object, in that location should be minimum of two points of observation is needed from different angles. Parallax is naught only a displacement of an object in the photo when point of ascertainment is shifted to another angle. In full general Measurement of parallax can be washed by ii ways as follows:

  • Floating marks
  • Parallax bar

Parallax and Measurement of Parallax


Construction of Map and Cartography

After collecting all photographs, it’south time to create or plot the map. In that location are several methods bachelor to plot the details of map and they are

  • Radial line method
  • Slotted template method
  • Stereoscopic method

Radial Line Method

Radial line method is a graphical method of plotting the map from vertical photographs. By this method we tin can set a planimetric map. Some kind of perspective properties are used in this method. Those are, a principal point is stock-still in the photograph and the objects near this point are gratis from error of tilt. The alter is position of an object due to tilt and ground relief are measured outwards from the main point. The location of point in two overlapping photographs can be corrected by the intersection of three rays from known points.
Radial Line Method

Slotted Template Method

Slotted template method is mechanical method of plotting. In this method templates are prepared which are null only enlarged images of standard scale photographs. These templates are made of transparent celluloid sheets or cardboards etc. The steps involved in plotting the map past slotted template method are every bit follows.

  1. Grooming of templates
  2. Transfer of principal points
  3. Choice and transfer of small-scale control points
  4. Selection and transfer of lateral control points
  5. Centre punching
  6. Slotting
  7. Assembly of templates
  8. Completion of plotting

The equipment used in slotted template method is uneconomical than graphical method only however it is rapid and more accurate.
Slotted Template Method

Stereoscopic Method

In Stereoscopic plotting method an instrument called stereo plotter or multiplex is used for preparing maps. The maps prepared past this method is of high precision. In this method, the instrument will help to view the overlapped surface area in three dimensional which help to view the spatial model. Then the model is measured and orthographically projected equally map. Information technology is more authentic and this method is used by big mapping organizations.
Stereoscopic Method
Read More than:
What is Contouring? Methods, Maps and Uses of Contours in Surveying
Plane Table Surveying with Methods and Examples
Sounding in Hydrographic Surveying – Methods of Locating Sounding
What is Triangulation Surveying? Operations, Applications and Advantages

Source: https://theconstructor.org/surveying/photogrammetry-aerial-photography-procedure-surveying/20357/

Posted by: Fusiontr.com