llpoints - Generates a list of (latitude, longitude) points on a line between two endpoints.

SYNOPSIS

llpoints  [ parameter=value ... ]  [ outputfile ]

Parameters are: latitude_1, longitude_1, latitude_2, longitude_2, shortest_path, num_intervals.

DESCRIPTION

llpoints generates a dataset containing a list of (latitude, longitude) points on a line defined by two endpoints, (latitude_1, longitude_1), and (latitude_2, longitude_2). The user specifies the number of intervals, which will be one less than the number of points generated. If shortest_path is specified, the earth is treated like a sphere and the points are chosen so they lie on the great circle connecting the two endpoints. Otherwise, points are generated based on constant latitude and longitude increments. For example:

      delta_lat = latitude_2  - latitude_1
      delta_lon = longitude_2 - longitude_1

      for i = 0, 1, ..., num_intervals
        lat[i] = latitude_1  + delta_lat * i
        lon[i] = longitude_1 + delta_lon * i

PARAMETERS

latitude_1, longitude_1

These two parameters specify the first endpoint. Values must be specified using standard latitude and longitude formats. See formats. There are no default values.

latitude_2, longitude_2

These two parameters specify the second endpoint. Values must be specified using standard latitude and longitude formats. See formats. There are no default values.

shortest_path

This parameter specifies how points will be generated. If shortest_path is yes, points will be generated on the great circle connecting the two endpoints. Otherwise, points will be generated based on constant latitude and longitude increments. The default value is yes.

num_intervals

This parameter specifies the number of desired intervals between the two endpoints. The number of points generated will be one greater than this number. num_intervals can be any positive integer. There is no default value.

EXAMPLES

% llpoints
output file    : char(255) ? points
latitude_1     : char( 15) ? 40.46n
longitude_1    : char( 15) ? 111.53w
latitude_2     : char( 15) ? 25n
longitude_2    : char( 15) ? 99.32w
shortest_path  : char(  3) ? [yes]
num_intervals  : int       ? 5
%
% contents points
printout       : char(  3) ? [no] n
Contents of File: points    Page 1

Dimension       Size            Coord           Scale      Offset
 num_points         6            ?                  1           0

Attribute       Type            Units           Value
 history         byte

Variable        Type            Units
 latitude        float           std_latitude
 longitude       float           std_longitude

Variable        Dimension       Size
 latitude        num_points         6
 longitude       num_points         6

Variable            BadValue    ValidMin    ValidMax       Scale      Offset
 latitude        -3.4028e+38 -3.4028e+38  3.4028e+38           1           0
 longitude       -3.4028e+38 -3.4028e+38  3.4028e+38           1           0

SEE ALSO

llslice, formats

Last Update: $Date: 1999/05/10 20:14:43 $