1Ppmglobe User Manual(0) Ppmglobe User Manual(0)
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6 ppmglobe - generate strips to glue onto a sphere
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10 ppmglobe [-background=colorname] [-closeok] stripcount [filename]
11 Minimum unique abbreviation of option is acceptable. You may use dou‐
13 ble hyphens instead of single hyphen to denote options. You may use
14 white space in place of the equals sign to separate an option name from
15 its value.
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20 This program is part of Netpbm(1).
21 ppmglobe does the inverse of a cylindrical projection of a sphere.
23 Starting with a cylindrical projection, it produces an image you can
24 cut up and glue onto a sphere to obtain the spherical image of which it
25 is the cylindrical projection.
26 What is a cylindrical projection? Imagine a map of the Earth on flat
28 paper. There are lots of different ways cartographers show the three
29 dimensional information in such a two dimensional map. The cylindrical
30 projection is one. You could make a cylindrical projection by putting
31 a light inside a globe and wrapping a rectangular sheet of paper around
32 the globe, touching the globe at the Equator. Then trace the image
33 that the light projects onto the paper. Lay the paper out flat and you
34 have a cylindrical projection.
35 Here's where ppmglobe comes in: Pass the image on that paper through
37 ppmglobe and what comes out the other side looks something like this:
38 Example of map of the earth run through ppmglobe
40 You could cut out the strips and glue it onto a sphere and you'd have a
42 copy of the original globe.
43 Note that cylindrical projections are not what you normally see as maps
45 of the Earth. You're more likely to see a Mercator projection. In the
46 Mercator projection, the Earth gets stretched North-South as well as
47 East-West as you move away from the Equator. It was invented for use
48 in navigation, because you can draw straight compass courses on it, but
49 is used today because it is pretty.
50 You can find maps of planets at maps.jpl.nasa.gov
52 ⟨http://maps.jpl.nasa.gov⟩ .
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56 stripcount is the number of strips ppmglobe is to generate in the out‐
57 put. More strips makes it easier to fit onto a sphere (less stretch‐
58 ing, tearing, and crumpling of paper), but makes you do more cutting
59 out of the strips.
60 The strips are all the same width. If the number of columns of pixels
62 in the image doesn't evenly divide by the number of strips, ppmglobe
63 truncates the image on the right to create nothing but whole strips.
64 In the pathological case that there are fewer columns of pixels than
65 the number of strips you asked for, ppmglobe fails.
66 Before Netpbm 10.32 (February 2006), instead of truncating the image on
68 the right, ppmglobe produces a fractional strip on the right.
69 filename is the name of the input file. If you don't specify this,
71 ppmglobe reads the image from Standard Input.
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76 -background=colorname
77 This specifies the color that goes between the strips.
78 Specify the color (color) as described for the argument of the
80 ppm_parsecolor() library routine ⟨libppm.html#colorname⟩ .
81 The default is black.
83 This option was new in Netpbm 10.31 (December 2005). Before
85 that, the background is always black.
86 -closeok
89 This means it is OK if the background isn't exactly the color
90 you specify. Sometimes, it is impossible to represent a named
91 color exactly due to the precision (i.e. maxval) of the image's
92 color space. If you specify -closeok and ppmglobe can't repre‐
93 sent the color you name exactly, it will use instead the closest
94 color to it that is possible. If you don't specify closeok,
95 ppmglobe fails in that situation.
96 This option was new in Netpbm 10.31 (December 2005).
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103 ppm(1)
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107 ppmglobe was new in Netpbm 10.16 (June 2003).
108 It is derived from Max Gensthaler's ppmglobemap.
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113 Max Gensthaler wrote a program he called ppmglobemap in June 2003 and
114 suggested it for inclusion in Netpbm. Bryan Henderson modified the
115 code slightly and included it in Netpbm as ppmglobe.
116netpbm documentation 23 February 2006 Ppmglobe User Manual(0)