select_stations

Section: WIN SYSTEM (1W)
Updated: 2004.1.29
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NAME

select_stations - Selects observation point of arbitrary zone from file in channel table format

SYNOPSIS

select_stations ch_file polygon_file

DESCRIPTION

Select_stations selects a line (channel) of observation point positioned inside a polygonal zone specified by polygon_file from a file of channel table format ch_file, and writes in the standard output. However, the channels of which latitude and longitude are omitted in ch_file are bypassed. Refer to win(1) for format of channel table file.
Format of polygon_file is as follows: Coordinates (latitude and longitude in degree are delimited by blank or tab) of vertices of a polygon are arranged in order of clock-wise with one point per line. It is necessary to close the polygon by making the last vertex coincide with the first one. It is allowed that vertices of a polygon are concave.

Select_stations checks each side of a polygon showing the zone in order of clock-wise, and when a point is found to the right (viewed from start point to end point) of the side closest to the point, it determines the point exists inside the polygon.

When select_stations is initiated without argument, brief usage is displayed.

OPTIONS

None.

SOURCE

`select_stations.c'

BUG

Serious bug found in the early program (Nov. 9, 1999 Version) was corrected in Jan. 28, 2004 Version.