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 affect 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 (with alpha channel stored in a PGM image, if applicable).
If you set GRASS_PNGFILE to a filename which ends in ".bmp", a 32-bpp
BMP file will be created (these are not readable by some older viewers).
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.
if TRUE, the PNG driver will initialize the image from
the contents of GRASS_PNGFILE.
if TRUE, the PNG driver will map GRASS_PNGFILE as its framebuffer,
rather than using memory. This only works with BMP files.
tells the raster library to use its built-in PNG driver rather
than connecting to an external monitor process using sockets. If
TRUE, there is no need to run d.mon start=PNG.
- 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
zlib home page), all which needs to
be installed for the PNG driver to work (it's worth it).
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 <phj (at) norgit.no> NORGIT AS
Rewritten by: Glynn Clements, 2003
Last changed: $Date: 2012-03-02 21:22:34 -0800 (Fri, 02 Mar 2012) $
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