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

WillemvanSchaik  (of  pnmtopng/pngtopnm fame) wrote this program in October 2009 and suggested it for
       inclusion in Netpbm.

       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  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 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 .

       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 latitude distance of
       the represented area and horizontal distance is proportional to angular longitude.

       This manual page was generated by the Netpbm tool 'makeman' from HTML source.  The  master  documentation
       is at

              http://netpbm.sourceforge.net/doc/pnmmercator.html

netpbm documentation                              October 2009                        PnmMercatorUserManual(1)

pnmmercator was new in Netpbm 10.49 (December 2009).

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

       In  addition  to  the options common to all programs based on libnetpbm (most notably -quiet, see  Common
       Options ), pnmmercator recognizes the following command line options:

       -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.

filenameisthenameoftheinputfile.Ifyoudon'tspecifythis,pnmmercatorreadstheimagefromstandardInput.

pnm(1) and pamscale(1) ppmglobe(1)

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.