Projection Parameters

Method used to describe the line along which an oblique mercator map projection is centered using the map projection origin and an azimuth. Used for Oblique Mercator Type B map projection.

Datum

There are two principal types of datums: vertical and horizontal. A vertical datum is a level surface to which heights are referred. In the United States, the generally adopted vertical datum for leveling operations is the national geodetic vertical datums of 1929 (differing slightly from mean sea level). The horizontal datum, used as a reference for position, is defined by: the latitude and longitude of an initial point, the direction of a line between this point and a specified second point, and the two dimensions which define the spheroid. In the United States, the initial point for the horizontal datum is located at Meades Ranch in Kansas

False Easting - Options are -1.0 X 10(8) to +1.0 X 10(8)

False Easting (FE) is the offset of the central meridan, entered in meters. The default results in no offset. False Easting is in the same units as the semi-major axis (radium of the equatorial axis of the ellipsoid). The value added to all "x" values in the rectangular coordinates for a map projection. This value frequently is assigned to eliminate negative numbers.

False Northing - Options are -1.0 X 10(8) to +1.0 X 10(8)

False Northing (FN) in the same units as the semi-major axis (radius of the equatorial axis of the ellipsoid). The value added to all "y" values in the rectangular coordinates for a map projection. This value frequently is assigned to eliminate negative numbers.

Scan Gap Interpolation - Options are 0 - 15 pixels

Interpolation values range from 0 to 15 pixels, with each pixel representing 30 meters. The default value for interpolation is 2 pixels, which is the heritage value for Level 1G processing of previous Landsat 7 SLC-off data.

Grid Cell Size for the Pan Band (8) - Options are 14.25, 15.00, 25.00, 28.50, 30.00, 50.00, 57.00, or 60.00

A grid cell size of 14.25, 15.00, 25.00, 28.50, 30.00, 50.00, 57.00, or 60.00 meters used by the Level 1 Product Generation System (LPGS) in creating image for pan band.
Pan grid cell size is automatically defaulted to when Reflective band grid size is selected.

Grid Cell Size for the Reflective Bands (1-5,7) - Options are 25.00, 28.50 or 30.00

A grid cell size of 25.00, 28.50 or 30.00 meters used by the LPGS in creating image for pan band.

Grid Cell Size for the Thermal Bands (6L, 6H) - Options are 25.00, 28.50, 30.00, 50.00, 57.00, or 60.00

A grid cell size of 25.00, 28.50, 30.00, 50.00, 57.00, or 60.00 meters used by the LPGS in creating image for pan band.
Thermal grid cell size is automatically defaulted to when Reflective band grid size is selected

Image Orientation - Options are NUP or NOM

NUP = The image data is geographically rotated to a North Up orientation (map).
NOM = Nominal system (path) orientation applied to the image data.

Lambert Conformal Conic - Example

Primarily used for equal-angle maps of regions with a predominant east/west extent. The following characteristics are applicable to the Lambert Conformal Conic projection.

Conic.
Conformal.
Parallels are unequally spaced arcs of concentric circles, more closely spaced near the center of the map.
Meridians are equally spaced radii of the same circles, cutting the parallels at right angles.
Scale is true along two standard parallels.
Pole in same hemisphere as standard parallels is a point; other pole is at infinity.

Latitude of First Standard Parallel - Options are -90.0 to 90.0

Line of constant latitude at which the surface of the Earth and the plane or developed surface intersect.

Latitude of Second Standard Parallel - Options are -90.0 to 90.0

Line of constant latitude at which the surface of the Earth and the plane or developed surface intersect.

Latitude of Center Line's First Point - Options are -90.0 to 90.0

Latitude of first point defining central geodetic line of projection.

Latitude of Center Line's Second Point - Options are -90.0 to 90.0

Latitude of second point defining central geodetic line of projection.

Latitude of Projection Origin - Options are -90.0 to 90.0

Latitude chosen as the origin of rectangular coordinates for a map projection.

Longitude of Center Line's First Point - Options are -180.0 to +180.0

Longitude of first point defining central geodetic line of projection.

Longitude of Center Line's Second Point - Options are -180.0 to +180.0

Longitude of second point defining central geodetic line of projection.

Longitude of Projection Origin (Central Meridian) - Options are -180.0 to +180.0

The line of longitude at the center of a map projection generally used as the basis for constructing the projection.

Oblique Mercator Type A - Example

Oblique Mercator (Hotine) A. Used primarily for mapping regions with an extent in the oblique direction and was used (before SOM) for mapping Landsat data. This projection uses two points that are on the central line and are near the edges of the region. The following characteristics are applicable to the Oblique Mercator (Hotine) A projection.

Cylindrical (oblique).
Conformal.
Parallels are complex curves.
Meridians are complex curves except for two meridians which are 180 degrees apart and are straight lines.
Scale becomes infinite 90 degrees from the central line.

Oblique Mercator Type B

Oblique Mercator (Hotine) B. Used primarily for mapping regions with an extent in the oblique direction and was used (before SOM) for mapping Landsat data. This projection uses a central point and an azimuth that passes through the point as the central line. The following characteristics are applicable to the Oblique Mercator (Hotine) B projection.

Cylindrical(oblique)
Conformal
Parallels are complex curves.
Meridians are complex curves except for two meridians which are 180 degrees apart and are straight lines.
Scale becomes infinite 90 degrees from the central line.

Polar Stereographic - Example

Primarily used for the mapping of the polar areas of the Earth, Moon, and other planets. The following characteristics are applicable to the Polar Stereographic projection.

Azimuthal.
Conformal.
Parallels are shown as arcs of circles.
All meridians are straight lines.
Scale increases away from the center of the projection.
Directions from the center of projection are true.

Polyconic - Example

Used to provide a low-distortion mapping of local areas. This projection is rarely used today. The following characteristics are applicable to the Polyconic projection.

Conic.
Neither conformal nor equal-area.
Parallels (except equator) are arcs of circles.
Meridians are complex curves (Central meridian and equator are straight lines).
Scale is true along each parallel and central meridian.
Free of distortion only along central meridian.

Resampling Method - Options are CC, NN and MTF

CC - Cubic Convolution = Uses a weighted average of values within a neighborhood of adjacent pixels. Images generally are much more attractive than other resampling methods, but the data are altered much more drastically.
NN - Nearest Neighbor = Assigns each "corrected" pixel the value from the nearest "uncorrected" pixel. Original data values are preserved unaltered in the image, yet noticeable positional errors, which can be especially severe in easily recognizable linear features where the realignment of pixels is obvious.
MTF = Modulation Transfer Function pixel resampling method.

Scale Factor at Projection Center - Options are 0.0 to 2.0

Scale factor at the center of the map projection. A multiplier for reducing a distance obtained from a map by computation or scaling to the actual distance at the projection origin. Scale Factor at Projection Origin > 0.0

Scale Factor of the Central Meridian - Options are 0.0 to 2.0

A multiplier for reducing a distance obtained from a map by computation or scaling to the actual distance along the central meridian. Scale Factor at Central Meridian > 0.0

Space Oblique Mercator - Example

Used for mapping imagery from Landsat and other satellites with nearly circular orbits. The following characteristics are applicable to the Space Oblique Mercator projection.

Modified cylindrical.
Basically conformal.
Parallels are curved lines.
Meridians are curved lines except at each polar approach.
Scale is true along ground track of satellite.

Transverse Mercator

Primarily used for regions which are predominantly extending north and south. The following characteristics are applicable to the Transverse Mercator projection.

Cylindrical (transverse).
Conformal.
Parallels are complex curves. The equator is a straight line.
Each meridian that is 90 degrees from the central meridian is a straight line. All other meridians are complex curves.
Scale is true along the central meridian or along two straight lines equidistant from and parallel to central meridian. Scale becomes infinite 90 degrees from central meridian.

Units for False Easting and Northing - Default Option is Meters

Typically meters or feet are used as units for False Easting and Northing. Meters only are used for Level1 products.

Universal Transverse Mercator - Example

An ellipsoidal Transverse Mercator projection to which specific parameters have been applied. The earth is divided into 60 zones which are 6 degrees wide.

Ground Control Point software automatically adds a false northing of 10,000,000 meters if the first coordinate is south of the equator. Problems may occur when working around the equator.

When working in the Southern Hemisphere, enter a negative zone code.

Zone Number - Options are -60 to 60

A grid system based on the transverse mercator projection, applied between latitudes 84 degrees north and 84 degrees south on the Earth's surface.

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U.S. Department of the Interior \| U.S. Geological Survey URL: http://edcsns17.usgs.gov/helpdocs/parameters/parameters.html Page Contact Information: custserv@usgs.gov Page Last Modified: Wednesday February 25, 2004