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 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.
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 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 .
PARAMETERS
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.
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
-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).
SEE ALSO
ppm(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)
