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Ppmglobe User Manual(0)                                Ppmglobe User Manual(0)



NAME
       ppmglobe - generate strips to glue onto a sphere


SYNOPSIS
       ppmglobe [-background=colorname] [-closeok] stripcount [filename]

       Minimum  unique  abbreviation  of option is acceptable.  You may use double hyphens instead of single hyphen to
       denote options.  You may use white space in place of the equals sign to separate an option name from its value.



DESCRIPTION
       This program is part of Netpbm(1).

       ppmglobe  does the inverse of a cylindrical projection of a sphere.  Starting with a cylindrical projection, it
       produces an image you can cut up and glue onto a sphere to obtain the spherical image of which it is the cylin-
       drical projection.

       What  is a cylindrical projection?  Imagine a map of the Earth on flat paper.  There are lots of different ways
       cartographers show the three dimensional information in such a two dimensional map.  The cylindrical projection
       is  one.   You could make a cylindrical projection by putting a light inside a globe and wrapping a rectangular
       sheet of paper around the globe, touching the globe at the Equator.   Then  trace  the  image  that  the  light
       projects onto the paper.  Lay the paper out flat and you have a cylindrical projection.

       Here's  where  ppmglobe  comes  in:  Pass the image on that paper through ppmglobe and what comes out the other
       side looks something like this:

       Example of map of the earth run through ppmglobe

       You could cut out the strips and glue it onto a sphere and you'd have a copy of the original globe.

       Note that cylindrical projections are not what you normally see as maps of the Earth.  You're  more  likely  to
       see  a  Mercator projection.  In the Mercator projection, the Earth gets stretched North-South as well as East-
       West as you move away from the Equator.  It was invented for use in navigation, because you can  draw  straight
       compass courses on it, but is used today because it is pretty.

       You can find maps of planets at maps.jpl.nasa.gov .


PARAMETERS
       stripcount  is  the number of strips ppmglobe is to generate in the output.  More strips makes it easier to fit
       onto a sphere (less stretching, tearing, and crumpling of paper), but makes you do  more  cutting  out  of  the
       strips.

       The  strips  are  all the same width.  If the number of columns of pixels in the image doesn't evenly divide by
       the number of strips, ppmglobe truncates the image on the right to create nothing but  whole  strips.   In  the
       pathological  case  that  there  are  fewer columns of pixels than the number of strips you asked for, ppmglobe
       fails.

       Before Netpbm 10.32 (February 2006), instead of truncating the image on the right, ppmglobe  produces  a  frac-
       tional strip on the right.

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



OPTIONS
       -background=colorname
              This specifies the color that goes between the strips.

              Specify the color (color) as described for the argument of the ppm_parsecolor() library routine .

              The default is black.

              This option was new in Netpbm 10.31 (December 2005).  Before that, the background is always black.


       -closeok
              This means it is OK if the background isn't exactly the color you specify.  Sometimes, it is  impossible
              to  represent  a  named color exactly due to the precision (i.e. maxval) of the image's color space.  If
              you specify -closeok and ppmglobe can't represent the color you name exactly, it will  use  instead  the
              closest color to it that is possible.  If you don't specify closeok, ppmglobe fails in that situation.

              This option was new in Netpbm 10.31 (December 2005).




SEE ALSO
       ppm(1) pnmmercator(1)


HISTORY
       ppmglobe was new in Netpbm 10.16 (June 2003).

       It is derived from Max Gensthaler's ppmglobemap.


AUTHORS
       Max  Gensthaler  wrote  a  program he called ppmglobemap in June 2003 and suggested it for inclusion in Netpbm.
       Bryan Henderson modified the code slightly and included it in Netpbm as ppmglobe.



netpbm documentation           23 February 2006        Ppmglobe User Manual(0)