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



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


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

       Minimum unique abbreviation of option is acceptable.  You may use  dou-
       ble 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 projection 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 pnmmercator transformation with a pamscale reduction in size.

       This  program can also convert a Mercator projection map back to a rec-
       tangular 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 cor-
       responding  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 nav-
       igators	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 latitude 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  dou-
	      ble 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 suggested it for inclusion in Netpbm.



netpbm documentation		 October 2009	    PnmMercator User Manual(0)
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