Digital Cameras, Linear Cameras, Displacements of Non-Nadiral Points, a Linear Digital Photogrammetric Camera (Especially for GATE-Geospatial 2022)

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In a digital camera, the focal plane is substituted by a sensor with tiny photocells that register the image (CCD10) . The form of disposal of the CCD gives rise to two types of digital photogrammetric cameras.

Linear Cameras

  • The camera has three parallel lines of 12K11 sensors, transversal to the flight direction. These lines have different inclinations: fore, nadir and aft position, as shown in the figure.
  • As these cameras are digital, they can collect information from different parts of the electromagnetic spectrum, not just in the visible part.
A Linear Digital Photogrammetric Camera

A linear digital photogrammetric camera

Thus, once a strip has been done, three continuous bands of images are obtained, which are composed by each of the lines captured by the sensors.

Photogrammetric Shot of a Strip with a Linear

Photogrammetric shot of a strip with a linear image

  • Therefore, an advantage of this type of cameras is that the whole ground appears in three images. This register involves the capture of all the points under the guidance of the nadir direction of the plane. When capturing the whole ground vertically, the generation of truthful orthophotographs is favoured.
  • These photos will be dealt with in chapter 5, as raised elements will not appear out of place in the photograph.
Displacements of Non-Nadiral Points

Displacements of non-nadiral points

  • Nevertheless, each line has its own projection centre, and it cannot be considered as a photogrammetric shot with typical geometry. This aspect considerably complicates the calculations of the photogrammetric process. Hence, this type of cameras needs to be complemented by a GPS and by INS/IMU12 that registers the data and coordinates of each line.
  • In addition, the photogrammetric instruments must be prepared to work with this atypical type of geometry, premise that almost all instruments fulfil nowadays.
GPS During the Flight and Leica ADS40 Camera

GPS during the flight and Leica ADS40 camera. (Source: Leica Geosystems) Matrix cameras

The Geometry of a Photograph Taken with a Digital Matrix Cam …

The geometry of a photograph taken with a digital matrix camera

  • The figure shows that these types of sensors are similar to aerial analogical cameras regarding their composition. Matrix cameras have 1Kx1K sensorial elements (1024x1024 pixels) , 2Kx2K, 3Kx2K, 4Kx4K, 4Kx7K, 7Kx9K, 5Kx10K, 9Kx9K. Among them, the most common ones are 3Kx2K and 4Kx4K, which, similar to the linear ones, can also record in other ranks of the electromagnetic spectrum.
  • These sensors have GPS and INS systems during the flight, yet it is not indispensable for them to have these systems, as it happened in the previous case, due to the fact that the geometry, as shown in the figure, is similar to an analogical camera. In this figure, it is possible to observe that, despite the fact that they are multi-objective cameras, the geometry is still the usual one.
  • One of the most updated matrix cameras is the one shown in the figure. It combines various objectives in its focal plane, producing partial matrix images that unite in a complete image of 17310 x 1131 pixels.
Vexcel՚s Ultra Cam XP Camera and Photogrammetric

Vexcel՚s Ultra cam XP camera and Photogrammetric shot with a multi-objective matrix

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