.\" Copyright (C) 2017 Alessandro Menti
.\"
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.TH FGELEV 1 2017-06-04 FlightGear "FlightGear man pages"
.SH NAME
fgelev \- Compute FlightGear scenery elevation for a given list of points
.SH SYNOPSIS
\fBfgelev\fR [\fB\-\-expire\fR \fInum\fR] [\fB\-\-print\-solidness\fR]
[\fB\-\-fg\-root\fR \fIrootdir\fR] [\fB\-\-fg\-scenery\fR \fIscenerydir\fR]
.SH DESCRIPTION
.B fgelev
is a standalone utility that, given a list of points on standard input, prints
the corresponding elevation for each of them on standard output. It can also
(optionally) print whether the material covering that point is solid or not.

The list of points must be in the following form:

    \fIid lon lat\fR

where \fIid\fR is an arbitrary identifier for the point, \fIlon\fR is the
longitude of the point and \fIlat\fR is the latitude of the point. Positive
longitudes (latitudes) correspond to points located in the Eastern (Northern)
hemisphere; negative ones correspond to points located in the Western
(Southern) hemisphere.

The list of elevations returned by
.B fgelev
is in the following form:

    \fIid: elev solid\fR

where \fIid\fR is the identifier of the point passed as input, \fIelev\fR is
the elevation of the point in meters (or \fB-1000\fR if the elevation of the
given point was not found) and \fIsolid\fR is:
.IP \(bu 3
the string
.B solid
if the parameter
.B \-\-print\-solidness
was passed to
.B fgelev
and the material covering the point is solid;
.IP \(bu 3
the string
.B \-
if the parameter
.B \-\-print\-solidness
was passed to
.B fgelev
and the material covering the point is not solid;
.IP \(bu 3
absent if the parameter
.B \-\-print\-solidness
was not passed to \fBfgelev\fR.
.SH OPTIONS
.TP
\fB\-\-expire\fR \fInum\fR
To speed up elevation data retrieval,
.B fgelev
uses an internal cache. This option lets the user specify the number of
requests after which, if a point was not queried in them, it should be marked
as expired. By default,
.B fgelev
expires points not queried in the last \fB10\fR requests.
.TP
\fB\-\-print\-solidness\fR
Require
.B fgelev
to print the solidness of the material covering the queried point. See the
.B DESCRIPTION
section for more details.
.TP
\fB\-\-fg\-root\fR \fIrootdir\fR
Set the FlightGear data root directory (\fB$FG_ROOT\fR) to \fIrootdir\fR. If
this option is not set,
.B fgelev
uses the path specified in the
.B FG_ROOT
environment variable or, absent that, the FlightGear data directory chosen at
the time the program was compiled.
.TP
\fB\-\-fg\-scenery\fR \fIscenerydir\fR
Set the FlightGear scenery directory (\fB$FG_SCENERY\fR) to \fIscenerydir\fR.
If this option is not set,
.B fgelev
uses the path specified in the
.B FG_SCENERY
environment variable or, absent that, the
.B Scenery
subdirectory inside \fB$FG_ROOT\fR.
.SH "EXIT STATUS"
.B fgelev
exits with
.B EXIT_SUCCESS
on success, with
.B EXIT_FAILURE
if it is unable to read data from standard input or to load the scenery.
.SH ENVIRONMENT
.IP "\fBFG_ROOT\fR" 4
If
.B FG_ROOT
is set and
.B \-\-fg\-root
is not set, it specifies the root data directory to use.
.IP "\fBFG_SCENERY\fR" 4
If
.B FG_SCENERY
is set and
.B \-\-fg\-scenery
is not set, it specifies the scenery directory to use.
.SH "SEE ALSO"
.BR fgfs (1)