![Vertical_perspective_SW](https://upload.wikimedia.org/wikipedia/commons/e/ec/Vertical_perspective_SW.jpg)
The General Perspective projection is a
map projection
In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and longit ...
. When the Earth is photographed from space, the camera records the view as a perspective projection. When the camera is aimed toward the center of the Earth, the resulting projection is called Vertical Perspective. When aimed in other directions, the resulting projection is called a Tilted Perspective.
Perspective and usage
The Vertical Perspective is related to the
stereographic projection,
gnomonic projection, and
orthographic projection. These are all true
perspective projections, meaning that they result from viewing the globe from some vantage point. They are also
azimuthal
An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north.
Mathematically, ...
projections, meaning that the projection surface is a plane tangent to the sphere. This results in correct directions from the center to all other points. The ''point of perspective'', or vantage point, for the General Perspective Projection is at a finite distance. It depicts the earth as it appears from some relatively short distance above the surface, typically a few hundred to a few tens of thousands of kilometers.
When tilted, the General Perspective projection, also called the tilted perspective projection, is not azimuthal (see second figure below); directions are not true from the central point, and the projection plane is not tangent to the sphere.
[
PROJ contributors (2020). PROJ coordinate transformation software library. Open Source Geospatial Foundation]
"Tilted perspective"
Tilted perspectives are common from aerial and low orbit photography, generally taken from at a height measured in kilometers to hundreds of kilometers, rather than the hundreds or thousands of kilometers typical of a vertical perspective. However,
Richard Edes Harrison
Richard Edes Harrison (March 11, 1901 – January 5, 1994) was an American Technical illustration, scientific illustrator and cartographer. He was the house cartographer of ''Fortune (magazine), Fortune'' and a consultant at Life (magazine), ''Lif ...
pioneered the use of this projection on strategic maps showing military theaters during WWII.
Some prominent Internet mapping tools also use the tilted perspective projection. For example,
Google Earth and
NASA World Wind
NASA WorldWind is an open-source (released under the NOSA license and the Apache 2.0 license) virtual globe. According to the website (https://worldwind.arc.nasa.gov/), "WorldWind is an open source virtual globe API. WorldWind allow ...
show the globe as it appears from space. These applications permit a wide variety of interactive pan and zoom operations, including fly-through simulations, mimicking pictures or movies taken with a hand-held camera from an airplane or spacecraft.
History
Some forms of the projection were known to the Greeks and Egyptians 2,000 years ago. It was studied by several French and British scientists in the 18th and 19th centuries. However, the projection had little practical value at that time; computationally simpler nonperspective azimuthal projections could be used instead.
Space exploration led to a renewed interest in the perspective projection. Now the concern was for a pictorial view from space, not for minimal distortion. A picture taken with a hand-held camera from the window of a spacecraft has a tilted vertical perspective, so the manned Gemini and Apollo space missions sparked interest in this projection.
See also
*
List of map projections
*
Map projection
In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and longit ...
References
{{DEFAULTSORT:General Perspective Projection
Map projections