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PnmMercator User Manual(0)					       PnmMercator User Manual(0)

NAME
       pnmmercator  - transform a worldmap from rectangular projection to Mercator projection and
       vice-versa

SYNOPSIS
       pnmmercator [-inverse] [-nomix] [-[v]verbose] [filename]

       Minimum unique abbreviation of option is acceptable.  You may use double  hyphens  instead
       of single hyphen to denote options.

DESCRIPTION
       This program is part of Netpbm(1)

       The  pnmmercator utility, converts a rectangular projection worldmap to a Mercator projec-
       tion format, as used for maps.google.com and many other online  maps.   The  map  used  as
       input  for  pnmmercator must have rows for -90 to 90 degrees latitude and columns for -180
       to +180 degrees longitude. The file will typically be twice as wide as high, but  this  is
       not   a	 requirement.	The   output   file   will   be  using	the  Mercator  projection
       <http://en.wikipedia.org/wiki/Mercator_projection>  and will get double the height of  the
       input file.

       Maps  using the Mercator projection are stretched more the closer a row is to the North or
       South Pole. The last few degrees (> 85 or < -85 degrees) are not part of a Mercator map at
       all  because  they  would  be  stretched too much and the rows close to the edge will show
       banding, because they originate from the same row in the original map.

       To overcome this, the program will by default do interpolation of pixel colors, which will
       eliminate  the banding effect, but will cause some blurring of the output. With the -nomix
       option, this interpolation of colors isn't applied. You can  obtain  the  highest  quality
       output  by  starting with an input map of high resolution, so that you can follow the pnm-
       mercator transformation with a pamscale reduction in size.

       This program can also convert a Mercator projection map back to a  rectangular  projection
       based.	As  said,  the Mercator map doesn't have information about the latitudes close to
       the poles.  Therefore the top rows in the output image will be identical and  copied  from
       the row corresponding with latitude of 85 degrees. The same at the bottom of the map.

       Pnmmercator  doesn't have any provision for scaling the image. You can scale by piping the
       output of the program through Netpbm programs such as pamscale.

       You can find maps to be used as input at flatplanet.sourceforge.net(1)

       or uic.edu/pape <http://www.evl.uic.edu/pape/data/Earth/> .

       The point of a Mercator projection map is that compass directions work on it.  If you draw
       a  straight line northeast from some point on the Mercator map, the line traces the course
       you would sail if you sailed a compass bearing of northeast from  that  spot.   Naturally,
       primitive  navigators appreciated that.	The biggest drawback of Mercator is that areas to
       the north and south appear much larger than they are in real life.  For example, Greenland
       appears	to  be larger than South America even though it only a ninth as large.	Note that
       areas away from the equator are stretched north-south as well as east-west.

       A rectangular projection is one where vertical distance is proportional to  angular  lati-
       tude  distance  of the represented area and horizontal distance is proportional to angular
       longitude.

PARAMETERS
       filename is the name of the input file.	If you don't specify this, pnmmercator reads  the
       image from standard Input.

OPTIONS
       <dl compact="compact">

       -inverse

	      With  this option a conversion from Mercator to degrees is applied.The output image
	      will have half the height of the input map.

       -nomix

	      Default behaviour is that color blending is applied in between two  adjacent  rows.
	      If  you  specify	the  -nomix  parameter there is no blending. The consequence is a
	      banding at the top and bottom of the map.  With this option, the	output	map  will
	      also consist of exactly the same colors as the input.

       -verbose and -vverbose

	      This  parameter outputs some additional information. If you double the 'v', it will
	      output debug data about the lat/long degree and Mercator conversions.

SEE ALSO
       pnm(1)
	and pamscale(1)

       ppmglobe(1)

HISTORY
       pnmmercator was new in Netpbm 10.49 (December 2009).

AUTHORS
       Willem van Schaik (of pnmtopng/pngtopnm fame) wrote this program in October 2009 and  sug-
       gested it for inclusion in Netpbm.

netpbm documentation			   October 2009 	       PnmMercator User Manual(0)
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