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 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.
This program is part of Netpbm(1)
ppmglobe does the inverse of a cylindrical projection of a sphere. Starting with a cylin-
drical 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 projec-
tion by tracing as folows: 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 origi-
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 <http://maps.jpl.nasa.gov> .
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, ppm-
globe 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.
This specifies the color that goes between the strips.
Specify the color (color) as described for the argument of the ppm_parsecolor()
library routine <libppm.html#colorname> .
The default is black.
This option was new in Netpbm 10.31 (December 2005). Before that, the background
is always black.
This means it is OK if the background isn't exactly the color you specify. Some-
times, 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 situ-
This option was new in Netpbm 10.31 (December 2005).
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
netpbm documentation 23 February 2006 Ppmglobe User Manual(0)