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NAME
PNG driver - driver to create PNG and PPM images.
(drivers)
DESCRIPTION
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.
USAGE
Environment variables
Several environment variables effect the operation
of the PNG driver.
- GRASS_WIDTH=xxx
the width of the image map (default is 640).
- GRASS_HEIGHT=yyy
the height of the image map (default is 480).
- GRASS_PNGFILE=filename
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).
- GRASS_BACKGROUNDCOLOR=RRGGBB
specifies the background color to use in RGB
notation (hex values). Default is 000000 (black).
- GRASS_TRANSPARENT=[TRUE|FALSE]
sets transparent background on (TRUE) or off (FALSE, default).
- GRASS_TRUECOLOR=[TRUE|FALSE]
sets true-color support. Default is TRUE
- GRASS_PNG_COMPRESSION=[0|1|9]
compression level of PNG files (0 = none, 1 = fastest, 9 = best, default is 6)
- GRASS_PNG_READ
if TRUE, the PNG driver will initialize the image from
the contents of GRASS_PNGFILE.
- GRASS_PNG_MAPPED
if TRUE, the PNG driver will map GRASS_PNGFILE as its framebuffer,
rather than using memory. This only works with BMP files.
- GRASS_RENDER_IMMEDIATE=[FALSE|TRUE|PNG|PS|HTML|cairo]
tells the raster library which driver to use. If
TRUE, the cairo driver is used if it is enabled, otherwise the PNG driver is used.
- GRASS_LINE_WIDTH
the default line width.
- GRASS_TEXT_SIZE
the default text size.
- GRASS_FRAME
contains 4 coordinates, top,bottom,left,right, defining the initial frame.
Example
# Define driver settings (here: bash shell syntax)
export GRASS_RENDER_IMMEDIATE=PNG
export GRASS_TRUECOLOR=TRUE
# Display raster map and vector polygons
d.rast somerastermap
d.vect somevectormap color=red
This writes a file named map.png in your current directory.
NOTES
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.
SEE ALSO
Display drivers
CAIRO driver,
PostScript driver,
d.rast,
d.vect
AUTHOR
Original version: Per Henrik Johansen <phj (at) norgit.no> NORGIT AS
Rewritten by: Glynn Clements, 2003
Last changed: $Date: 2011-01-22 06:14:43 -0800 (Sat, 22 Jan 2011) $
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