|
 A Projected
coordinate system (PCS) is a two-dimensional planar
surface. However, the Earth's surface is three-dimensional. Transforming
three-dimensional space onto a two-dimensional surface is called projection.
Projection formulas are mathematical expressions that convert data from
a geographical location (latitude and longitude) on a sphere or spheroid
to a corresponding location (x and y) on a flat, two dimensional surface.
The PCS uses two axes: the x-axis, representing
east-west, and the y-axis, representing north-south. They intersect at
the origin, (0,0). Locations are defined relative to the origin, using
the notation (x,y), where x refers to the distance along the horizontal
axis, and y refers to the distance along the vertical axis.
The projected or planar coordinate system locates points relative to the
point of origin (0,0) and the x- and y-axes. Points below the x-axis or
to the left of the y-axis have negative values.
A PCS inherits the components of a geographic coordinate
system and also has:
- Projection: The mathematical transformation used to convert from geographic
coordinates to planar (projected) coordinates.
- Parameters: Parameters used in the transformation. These parameters are
specific to the projection.
- Units: Linear measurement for coordinates on the plane.
The following example is the string representation of the California State Plane
Zone #1, which is a projected coordinate system.
| PROJCS["NAD_1983_California_I",GEOGCS["GCS_North_American_1983",
DATUM["D_North_American_1983",SPHEROID["GRS_1980",6378137,298.257222101]], PRIMEM["Greenwich",0],UNIT["Degree",0.0174532925199433]],
PROJECTION["Lambert_Conformal_Conic"],PARAMETER["False_Easting",2000000],
PARAMETER["False_Northing",500000],PARAMETER["Central_Meridian",122],
PARAMETER["Standard_Parallel_1",40],PARAMETER["Standard_Parallel_2",
41.66666666666666],PARAMETER["Latitude_Of_Origin",39.33333333333334],
UNIT["Meter",1]] |
See also
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