man > ppmglobe(1)

Ppmglobe User Manual(1)                General Commands Manual               Ppmglobe User Manual(1)

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 sep‐
       arate 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 cylindri‐
       cal 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  dimen‐
       sional  map.   The cylindrical projection is one.  You could make a cylindrical projection by
       tracing as follows: wrap a rectangular sheet of paper around the globe, touching the globe at
       the Equator.  For each point of color on the globe, run a horizontal line from  the  axis  of
       the  globe  through that point and out to the paper.  Mark the same color on the paper there.
       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  in‐
       vented  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 fractional 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
       In  addition  to  the options common to all programs based on libnetpbm (most notably -quiet,
       see  Common Options ), ppmglobe recognizes the following command line options:




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

              Specify the color (color) as described  for  the  argument of the pnm_parsecolor() li‐
              brary 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 because  of  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).




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 inclu‐
       sion in Netpbm.  Bryan Henderson modified the code slightly and included it in Netpbm as ppm‐
       globe.

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

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

netpbm documentation                      23 February 2006                   Ppmglobe User Manual(1)