ppmglobe



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



ppmglobe - generate strips to glue onto a sphere



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


       Minimum  unique abbreviation of option is acceptable.  You may use dou-
       ble 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.



       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 cylindrical 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 .


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

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






       -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  repre-
              sent 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).



              ppm(1)


       ppmglobe was new in Netpbm 10.16 (June 2003).

       It is derived from
        Max Gensthaler’s ppmglobemap .


       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           29 November 2005        Ppmglobe User Manual(0)

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