Introduction
Photogrammetry is quite a simple technology. Just as our two eyes allow us to see in three dimensions, taking two photographs from slightly different positions will allow us to achieve the same result - stereoscopic vision. The real trick is how to take this 3D representation of the world and measure it. Photogrammetry then is the science of optimising photography for and the extraction of measurements, in 2 or 3 dimensions, from photographs.
In general, photogrammetry can be divided into two broad classes: those that mimic the human vision system and those that don't. The former goes by the name "stereo photogrammetry" and the latter "convergent photogrammetry". I'm sure you'll find many other classes too, but these are the two I will use and discuss here.
What is interesting is that the same basic principles can be applied to both types, and if I was pedantic enough I would say that stereo photogrammetry is just a special case of convergent photogrammetry. But whole textbooks have been written about each type (more on stereo than convergent) so I'll accept they can, and should, be treated differently. Once we look in detail at both types, it will become obvious why this evolution has happened.
Photogrammetry is a part of a broad science called remote sensing. Remote sensing encompasses all those techniques that can be used to obtain information about an object without touching it. There are many definitions to this field of study. In the world of Geomatics, some other examples are hydrographic surveying, satellite imaging and intersection survey.
Photogrammetry uses photographs either in hard copy or digital form to obtain the desired information. Some people think of a photograph only as a hard copy image. To save confusion, I will use the term image to represent any the item upon which we measure when doing photogrammetry.
Photogrammetry is quite a simple technology. Just as our two eyes allow us to see in three dimensions, taking two photographs from slightly different positions will allow us to achieve the same result - stereoscopic vision. The real trick is how to take this 3D representation of the world and measure it. Photogrammetry then is the science of optimising photography for and the extraction of measurements, in 2 or 3 dimensions, from photographs.
In general, photogrammetry can be divided into two broad classes: those that mimic the human vision system and those that don't. The former goes by the name "stereo photogrammetry" and the latter "convergent photogrammetry". I'm sure you'll find many other classes too, but these are the two I will use and discuss here.
What is interesting is that the same basic principles can be applied to both types, and if I was pedantic enough I would say that stereo photogrammetry is just a special case of convergent photogrammetry. But whole textbooks have been written about each type (more on stereo than convergent) so I'll accept they can, and should, be treated differently. Once we look in detail at both types, it will become obvious why this evolution has happened.
Photogrammetry is a part of a broad science called remote sensing. Remote sensing encompasses all those techniques that can be used to obtain information about an object without touching it. There are many definitions to this field of study. In the world of Geomatics, some other examples are hydrographic surveying, satellite imaging and intersection survey.
Photogrammetry uses photographs either in hard copy or digital form to obtain the desired information. Some people think of a photograph only as a hard copy image. To save confusion, I will use the term image to represent any the item upon which we measure when doing photogrammetry.
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