PNG driver - driver to create PNG and PPM images
The PNG driver generates PNG and PPM images from GRASS display commands.
Per default PNG files are written with this driver. It is started as 'pseudo' monitor
(image file instead) and when stopped, all output from previously used
display commands are written to the PNG image file.
Several environment variables effect the operation
of the PNG driver.
the width of the image map (default is 640).
the height of the image map (default is 480).
the filename to put the resulting image in, default is map.png.
If you set GRASS_PNGFILE to a filename which ends in ".ppm", a PPM
file will be created.
specifies the background color to use in RGB
notation (hex values). Default is 000000 (black).
sets transparent background on (TRUE) or off (FALSE, default).
sets true-color support
compression level of PNG files (0 = none, 1 = fastest, 9 = best; default is 6)
if set to "TRUE", the image file will be written after each
operation (i.e. whenever a client disconnects), rather than
only being written out when the driver terminates.
- Define driver settings (here: bash shell syntax)
- Start up the driver
- Display raster map and vector polygons
d.vect somevectormap color=red
- Stop the driver subsequently. This will write a
file named map.png to be created in your current directory:
The PNG driver uses the libpng (see the libpng
home page) and zlib (see the
page), all which needs to be installed for the PNG driver to work (it's
The resolution of the PNG raster map is defined by the map
extents. Use g.region -p to get the number of rows and cols and
use the environment variables to set the PNG size. If you would like a
larger image, multiply both rows and cols by the same whole number to
preserve the aspect ratio.
Further PNG file processing (e.g. quantization to 1 bit for monochrome images)
can be done with 'pnmquant' of the netpbm tools.
Original version: Per Henrik Johansen
Rewritten by Glynn Clements, 2003
Last changed: $Date: 2007/08/23 13:40:51 $
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