master, master2, master4 - Generates a base map and projection for a user specified area.

SYNOPSIS

master  [ parameter=value ... ]  [ outputfile ]
master2  [ parameter=value ... ]  [ outputfile ]
master4  [ parameter=value ... ]  [ outputfile ]

Parameters for master are: projectioncenter_latcenter_lonnum_linesnum_samples, pixel_width, pixel_height, standard_lat, rotate_angle, earth_radius, flattening, move_center, new_center_lat, new_center_lon.

Parameters for master2 are: projection, min_lat, max_lat, min_lon, max_lon, square_aspect, num_lines, num_samples, estim_center, center_lat, center_lon, earth_radius, flattening, corner_edges, standard_lat, view_radians, rotate_angle.

Parameters for master4 are: projection, estim_center, center_lat, center_lon, rotate_angle, standard_lat, earth_radius, flattening, corner_edges, view_radians, num_lines, num_samples, up_left_lat, up_left_lon, low_left_lat, low_left_lon, up_right_lat, up_right_lon, low_right_lat, low_right_lon.

DESCRIPTION

These functions generate a master dataset containing attributes that parameterize an earth transform. This transform relates line and sample coordinates to latitude and longitude coordinates for a user-defined geographical region using a user-specified map projection. master defines the region by the center latitude and longitude, and the pixel size at the center. master2 defines the region using a bounding latitude/longitude box. master4 defines the region using corner (lat/lon) coordinates.

Master datasets are used by a variety of ingest functions such as hrptin and rtdin to limit data extraction to only the rectangular subset of sensor data that intersects the geographical area specified by a master dataset.

Master datasets are most often used to interpolate data in sensor coordinates onto the region defined by the master dataset. This is done by using registration functions such as fastreg. fastreg takes all of the data within an input dataset and interpolates that data onto the grid defined by the master dataset. Data falling outside the master dataset are discarded by fastreg.

Master datasets can also be used by passcover and catcover to determine whether a satellite pass intersects a master dataset.

Master datasets contain two dimensions line and sample, plus attributes that describe the map projection. Master datasets also contain a null (empty) variable called master with line and sample dimensions. This variable can be displayed to create and blank background over which various overlays (geopolitical boundaries, lat/lon grids) can be drawn.

PARAMETERS

projection
Name of the map projection. Valid responses are (stereographic, rectangular, orthographic, polarstereo, equidist_azim, mercator, utm, polyconic, lambert_azim, lambert_conic, albers_conic, mollweide, cylindrical, perspective). There is no default.
polarstereo is not supported by master2.
polarstereo, lambert_conic, and albers_conic projections are based on a geodetic (elliptic) earth. All other projections are based on a spherical earth.
These map projections are defined in the publication entitled Map Projections used by the U.S. Geological Survey, Bulletin 1532 by John P. Snyder.
For minimal distortion, rectangular, cylindrical and mercator projections should not be used for maps centered near the poles.
estim_center
Option to estimate the mathematical projection center in master2 and master4. Valid responses are (yes, no). The default is yes.
center_lat, center_lon
Center (lat, lon) coordinates used for the mathematical definition of the map projection. They may not appear at the center of the master dataset, however, depending on other parameters. See formats for valid ways to specify latitude and longitude. There is no default value.
[ Exception. When projection=polarstereo, the mathematical center latitude is taken to be the nearest pole to the user specified center_lat. The master data center is moved to the user specified center_lat and center_lon by adjusting the master dataset's affine transform attribute. ]
center_lat and center_lon are not used by master2 or master4 unless estim_center=no.
min_lat, max_lat
Latitude limits used by master2. See formats for valid ways to specify latitude. min_lat must be less than max_lat. There is no default.
 
corner_edges
For master2, if corner_edges=yes, latitude and longitude limits refer to the outer edges of the outer pixels. If corner_edges=no, latitude and longitude limits refer to the centers of the outer pixels. The default is corner_edges=yes
For master4, if corner_edges=yes, latitudes and longitudes apply to the outer corner of the corner pixels. If corner_edges=no, latitudes and longitudes apply to the centers of the corner pixels.
The default is corner_edges=yes
 
min_lon, max_lon
Longitude limits used by master2. See formats for valid ways to specify longitude. min_lat is the leftmost longitude; max_lon is the rightmost longitude. There is no default.
up_left_lat, up_left_lon, up_right_lat, up_right_lon
Upper left corner and upper right corner (lat, lon) coordinates used by master4. They apply to the center of the corner pixels, not to the outer corner. See formats for valid ways to specify latitude and longitude. There are no defaults.
low_left_lat, low_left_lon, low_right_lat, low_right_lon
Lower left corner and lower right corner (lat, lon) coordinates used by master4. They apply to the center of the corner pixels, not to the outer corner. See formats for valid ways to specify latitude and longitude. There are no defaults.
square_aspect
Option in master2 to make pixel width the same as pixel height. If square_aspect=yes, only num_samples is user specified; num_lines is computed using the lat/lon limits and num_samples. In this case, the pixel height and width near the center of the master dataset will rarely be a round number.
If square_aspect=no, chances are that the pixel aspect near the center of the master dataset will not be one.
Valid responses are (yes, no). The default is yes.
num_lines, num_samples
Height and width of the master dataset in pixels. There is no default. In the case of master2, if square_aspect=yes, only num_samples is user specified; num_lines is computed.
pixel_width, pixel_height
Pixel width and height in kilometers, at the projection center, before any rotation. Note, for projections polarstereo, lambert_conic and albers_conic, pixel size is enforced along the standard parallels, not at the center.
The valid range for pixel_width and pixel_height is [.001, 1000.]. The default is 1.1132 km = 0.01*(degree of latitude). These parameters are used only by master.
standard_lat
If projection=polarstereo or projection=cylindrical, then standard_lat is the standard parallel of the projection, e.g., the latitude at which the plane intersects the earth. The default for polarstereo is 70. The default for cylindrical is the value of center_lat.
If the projection is lamber_conic or albers_conic, then standard_lat is the distance from the center_latitude to the standard parallels, e.g., the latitudes where the cone intersects the earth. The default is 5.
Otherwise, standard_lat does not apply. standard_lat is not used by master2 or master4 unless estim_center=no.
 
view_radians
If projection=perspective, then view_radians is the radius of the viewing point in space measured in radians. The valid range is [1., 10.]. The default is 6.611, which is the approximate orbital radius for geostationary satellites.
 
earth_radius
Earth equatorial radius. The default is 6378.137 kilometers (WGS84). This parameter is OPTIONAL for master and master2, and must be supplied on the command line. The user is prompted for this parameter in master4.
 
flattening
Earth flattening. The default is 0.003352810665 (WGS84). Note that flattening does not apply to those projections based on a spherical earth. This parameter is OPTIONAL for master and master2, and must be supplied on the command line. The user is prompted for this parameter in master4.

rotate_angle

This parameter allows the north end of the master dataset to be rotated clockwise through this angle. Normally, line 1 is the northern most line. The valid range is [-180 to 180]. The default is 0.
rotate_angle is not used by master2 or master4 unless estim_center=no.
move_center, new_center_lat, new_center_lon
Option in master to move the master dataset center away from the mathematical projection center. new_center_lat and new_center_lon are used only if move_center=yes. See formats for ways to specify latitude and longitude.
When projection=polarstereo, move_center is not used. The center of the master dataset is moved to the user specified center_lat and center_lon. See the Exception noted above.

EXAMPLES

This example illustrates the building of a base map located in the vicinity of the Hawaiian Islands. The base map defines an approximately square area, 1024x1.1132 kilometers on a side.

% master
output file     : char(255) ? [Master]
projection      : char( 13) ? rect
center_lat      : char( 15) ? 21 N
center_lon      : char( 15) ? 157 W
num_lines       : int       ? 1024
num_samples     : int       ? 1024
pixel_width     : real      ? [1.1132]
pixel_height    : real      ? [1.1132]
rotate_angle    : real      ? [0]
move_center     : char(  3) ? [yes]

The next two examples illustrate the usage of master2. The master datasets are bounded by the rectangle [30n, 50n] X [120w, 90w]. Both methods for controlling pixel width/height aspect ratio are shown.

% master2
output file    : char(255) ? [Master]
projection     : char( 13) ? stereo
min_lat        : char( 15) ? 30 n
max_lat        : char( 15) ? 50 n
min_lon        : char( 15) ? 120 w
max_lon        : char( 15) ? 90 w
square_aspect  : char(  3) ? [yes]
num_samples    : int       ? 1000
master2: 836 lines, 1000 samples,
         2.91724 km pixel height, 2.91724 km pixel width
%
% master2
output file    : char(255) ? [Master]
projection     : char( 13) ? stereo
min_lat        : char( 15) ? 30 n
max_lat        : char( 15) ? 50 n
min_lon        : char( 15) ? 120 w
max_lon        : char( 15) ? 90 w
square_aspect  : char(  3) ? [yes] n
num_lines      : int       ? 850
num_samples    : int       ? 1000
master2: 850 lines, 1000 samples,
         2.86643 km pixel height, 2.91724 km pixel width

The last example illustrates the usage of master4. Note, that because the projection is rectangular, and the corners are perfect, the pixel errors are extremely small. This would not normally be the case with other projections.

% master4
output file    : char(255) ? [Master]
projection     : char( 13) ? [utm] rect
estim_center   : char(  3) ? [yes]
num_lines      : int       ? 1024
num_samples    : int       ? 1024
up_left_lat    : char( 15) ? 40n
up_left_lon    : char( 15) ? 140w
low_left_lat   : char( 15) ? 30n
low_left_lon   : char( 15) ? 140w
up_right_lat   : char( 15) ? 45n
up_right_lon   : char( 15) ? 120w
low_right_lat  : char( 15) ? 35n
low_right_lon  : char( 15) ? 120w
Pixel errors: max = 5.08423e-13, mean = 4.21531e-13, std dev = 1.97176e-13
%

SEE ALSO

etx, formats, fastreg.

NOTES

master4 uses least squares to determine the best values for the et_affine attribute. Pixel height, width, and the angle of rotation are encoded within this attribute. The affine transform is discussed on the etx page.


Last Update: $Date: 1998/09/01 21:57:23 $