pngdriver(1grass) GRASS GIS User's Manual pngdriver(1grass)
PNG DISPLAY DRIVER
PNG display driver to create PNG, PPM, or BMP images.
DESCRIPTION
The PNG driver generates PNG, PPM, or BMP images from GRASS display
commands. Per default PNG files are written with this driver. This
driver is used by default if Cairo driver is not available.
USAGE
Environment variables
The PNG driver can be enabled by setting GRASS_RENDER_IMMEDIATE vari-
able, eg.
export GRASS_RENDER_IMMEDIATE=png
Several environment variables affect the operation of the PNG driver:
• GRASS_RENDER_WIDTH=xxx
the width of the image map (default is 640).
• GRASS_RENDER_HEIGHT=yyy
the height of the image map (default is 480).
• GRASS_RENDER_BACKGROUNDCOLOR=RRGGBB
specifies the background color to use in RGB notation (hex or
R:G:B values). Named colors are also supported. Default is
FFFFFF (white).
• GRASS_RENDER_TRANSPARENT=[TRUE|FALSE]
sets transparent background on (TRUE) or off (FALSE, default).
• GRASS_RENDER_TRUECOLOR=[TRUE|FALSE]
sets true-color support. Default is TRUE.
• GRASS_RENDER_FILE=filename
the filename to put the resulting image in, default is map.png.
If you set GRASS_RENDER_FILE 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_RENDER_FILE
to a filename which ends in ".bmp", a 32-bpp BMP file will be
created (these are not readable by some older viewers).
• GRASS_RENDER_FILE_COMPRESSION=[0|1|9]
compression level of PNG files (0 = none, 1 = fastest, 9 =
best, default is 6)
• GRASS_RENDER_FILE_READ
if TRUE, the PNG driver will initialize the image from the con-
tents of GRASS_RENDER_FILE.
• GRASS_RENDER_FILE_MAPPED
if TRUE, the PNG driver will map GRASS_RENDER_FILE as its
framebuffer, rather than using memory. This only works with BMP
files.
Example
export GRASS_RENDER_IMMEDIATE=png
export GRASS_RENDER_TRUECOLOR=TRUE
g.region raster=elevation
d.rast elevation
d.vect roadsmajor 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 output images is defined by current region ex-
tents. Use g.region -p to get the number of rows and cols and use the
environment variables to set the image 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
Cairo driver, PS driver, HTML driver, variables
d.rast, d.vect, d.mon, d.erase, d.redraw
AUTHOR
Original version: Per Henrik Johansen <phj (at) norgit.no>
Rewritten by: Glynn Clements, 2003
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GRASS 7.8.7 pngdriver(1grass)
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