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PLANIMETER(1)		    GeographicLib Utilities		 PLANIMETER(1)

NAME
       Planimeter -- compute the area of geodesic polygons

SYNOPSIS
       Planimeter [ -r ] [ -s ]	[ -l ] [ -e a f	] [ -w ] [ -p prec ] [ -G | -E
       | -Q | -R ] [ --comment-delimiter commentdelim ]	[ --version | -h |
       --help ]	[ --input-file infile |	--input-string instring	] [
       --line-separator	linesep	] [ --output-file outfile ]

DESCRIPTION
       Measure the area	of a geodesic polygon.	Reads polygon vertices from
       standard	input, one per line.  Vertices may be given as latitude	and
       longitude, UTM/UPS, or MGRS coordinates,	interpreted in the same	way as
       GeoConvert(1).  (MGRS coordinates signify the center of the
       corresponding MGRS square.)  The	end of input, a	blank line, or a line
       which can't be interpreted as a vertex signals the end of one polygon
       and the start of	the next.  For each polygon print a summary line with
       the number of points, the perimeter (in meters),	and the	area (in
       meters^2).

       The edges of the	polygon	are given by the shortest geodesic between
       consecutive vertices.  In certain cases,	there may be two or many such
       shortest	geodesics, and in that case, the polygon is not	uniquely
       specified by its	vertices.  This	only happens with very long edges (for
       the WGS84 ellipsoid, any	edge shorter than 19970	km is uniquely
       specified by its	end points).  In such cases, insert an additional
       vertex near the middle of the long edge to define the boundary of the
       polygon.

       By default, polygons traversed in a counter-clockwise direction return
       a positive area and those traversed in a	clockwise direction return a
       negative	area.  This sign convention is reversed	if the -r option is
       given.

       Of course, encircling an	area in	the clockwise direction	is equivalent
       to encircling the rest of the ellipsoid in the counter-clockwise
       direction.  The default interpretation used by Planimeter is the	one
       that results in a smaller magnitude of area; i.e., the magnitude	of the
       area is less than or equal to one half the total	area of	the ellipsoid.
       If the -s option	is given, then the interpretation used is the one that
       results in a positive area; i.e., the area is positive and less than
       the total area of the ellipsoid.

       Only simple (i.e., non-self-intersecting) polygons are supported	for
       the area	computation.  Polygons may include one or both poles.  There
       is no need to close the polygon.

OPTIONS
       -r  toggle whether counter-clockwise traversal of the polygon returns a
	   positive (the default) or negative result.

       -s  toggle whether to return a signed result (the default) or not.

       -l  toggle whether the vertices represent a polygon (the	default) or a
	   polyline.  For a polyline, the number of points and the length of
	   the path joining them is returned; the path is not closed and the
	   area	is not reported.

       -e a f
	   specify the ellipsoid via the equatorial radius, a and the
	   flattening, f.  Setting f = 0 results in a sphere.  Specify f < 0
	   for a prolate ellipsoid.  A simple fraction,	e.g., 1/297, is
	   allowed for f.  By default, the WGS84 ellipsoid is used, a =
	   6378137 m, f	= 1/298.257223563.  If entering	vertices as UTM/UPS or
	   MGRS	coordinates, use the default ellipsoid,	since the conversion
	   of these coordinates	to latitude and	longitude always uses the
	   WGS84 parameters.

       -w  toggle the longitude	first flag (it starts off); if the flag	is on,
	   then	when reading geographic	coordinates, longitude precedes
	   latitude (this can be overridden by a hemisphere designator,	N, S,
	   E, W).

       -p prec
	   set the output precision to prec (default 6); the perimeter is
	   given (in meters) with prec digits after the	decimal	point; the
	   area	is given (in meters^2) with (prec - 5) digits after the
	   decimal point.

       -G  use the series formulation for the geodesics.  This is the default
	   option and is recommended for terrestrial applications.  This
	   option, -G, and the following three options,	-E, -Q,	and -R,	are
	   mutually exclusive.

       -E  use "exact" algorithms (based on elliptic integrals)	for the
	   geodesic calculations.  These are more accurate than	the (default)
	   series expansions for |f| > 0.02.  (But note	that the
	   implementation of areas in GeodesicExact uses a high	order series
	   and this is only accurate for modest	flattenings.)

       -Q  perform the calculation on the authalic sphere.  The	area
	   calculation is accurate even	if the flattening is large, provided
	   the edges are sufficiently short.  The perimeter calculation	is not
	   accurate.

       -R  The lines joining the vertices are rhumb lines instead of
	   geodesics.

       --comment-delimiter commentdelim
	   set the comment delimiter to	commentdelim (e.g., "#"	or "//").  If
	   set,	the input lines	will be	scanned	for this delimiter and,	if
	   found, the delimiter	and the	rest of	the line will be removed prior
	   to processing.  For a given polygon,	the last such string found
	   will	be appended to the output line (separated by a space).

       --version
	   print version and exit.

       -h  print usage and exit.

       --help
	   print full documentation and	exit.

       --input-file infile
	   read	input from the file infile instead of from standard input; a
	   file	name of	"-" stands for standard	input.

       --input-string instring
	   read	input from the string instring instead of from standard	input.
	   All occurrences of the line separator character (default is a
	   semicolon) in instring are converted	to newlines before the reading
	   begins.

       --line-separator	linesep
	   set the line	separator character to linesep.	 By default this is a
	   semicolon.

       --output-file outfile
	   write output	to the file outfile instead of to standard output; a
	   file	name of	"-" stands for standard	output.

EXAMPLES
       Example (the area of the	100km MGRS square 18SWK)

	  Planimeter <<EOF
	  18n 500000 4400000
	  18n 600000 4400000
	  18n 600000 4500000
	  18n 500000 4500000
	  EOF
	  => 4 400139.53295860 10007388597.1913

       The following code takes	the output from	gdalinfo and reports the area
       covered by the data (assuming the edges of the image are	geodesics).

	  #! /bin/sh
	  egrep	'^((Upper|Lower) (Left|Right)|Center) '	|
	  sed -e 's/d /d/g' -e "s/' /'/g" | tr -s '(),\r\t' ' '	| awk '{
	      if ($1 $2	== "UpperLeft")
		  ul = $6 " " $5;
	      else if ($1 $2 ==	"LowerLeft")
		  ll = $6 " " $5;
	      else if ($1 $2 ==	"UpperRight")
		  ur = $6 " " $5;
	      else if ($1 $2 ==	"LowerRight")
		  lr = $6 " " $5;
	      else if ($1 == "Center") {
		  printf "%s\n%s\n%s\n%s\n\n", ul, ll, lr, ur;
		  ul = ll = ur = lr = "";
	      }
	  }
	  ' | Planimeter | cut -f3 -d' '

SEE ALSO
       GeoConvert(1), GeodSolve(1).

       An online version of this utility is availbable at
       <http://geographiclib.sourceforge.net/cgi-bin/Planimeter>.

       The algorithm for the area of geodesic polygon is given in Section 6 of
       C. F. F.	Karney,	Algorithms for geodesics, J. Geodesy 87, 43-55 (2013);
       DOI <https://dx.doi.org/10.1007/s00190-012-0578-z>; addenda:
       <http://geographiclib.sourceforge.net/geod-addenda.html>.

AUTHOR
       Planimeter was written by Charles Karney.

HISTORY
       Planimeter was added to GeographicLib,
       <http://geographiclib.sourceforge.net>, in version 1.4.

GeographicLib 1.46		  2016-02-14			 PLANIMETER(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXAMPLES | SEE ALSO | AUTHOR | HISTORY

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