Environmentvariables
The HTML driver can be enabled by setting GRASS_RENDER_IMMEDIATE variable, eg.
export GRASS_RENDER_IMMEDIATE=html
Several environment variables affect the operation of the HTML 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_HTMLTYPE=type
type of image map to create (default is CLIENT):
CLIENT Netscape/IE client-side image map (NAME="map").
APACHE Apache/NCSA server-side image map.
RAW Raw url and polygon vertices (urlx1y1x2y2.....), suitable for conversion to
CERN server format, or any other format with user supplied conversion program.
• GRASS_RENDER_FILE=filename
specifies the resulting file to store the html image map, default is htmlmap. Files without
absolute path names are written in the current directory where the driver was started.
Anyexistingfileofthesamenameisoverwrittenwithoutwarning.
• GRASS_RENDER_HTMLMINDIST=n
specifies the minimum distance in pixels that a point must change from the previous point to keep
in the list of vertices for a polygon. The default is 2, which means that a point’s x and y
difference from the previous point must change by a number of pixels greater than this value.
This parameter helps to eliminate closely spaced points.
• GRASS_RENDER_HTMLMINBBOX=n
specifies the minimum bounding box dimensions to record a polygon as a clickable area. The
default is 2, which means that a polygon with a bounding box of less than this value is not
included. This parameter helps to eliminate polygons than are a point or line.
• GRASS_RENDER_HTMLMAXPOINTS=n
specifies the maximum number of vertices included in a polygon’s clickable area. The default is
99. Some browsers can only accommodate polygons of 100 vertices or less. The HTMLMAP driver
automatically ensures that a polygon is closed by making the last point the same as the first
point.
Example
Start up the driver
g.region vector=zipcodes_wake
d.mon start=html
Display text strings (HREF’s) and polygons
echo "https://en.wikipedia.org/wiki/Raleigh,_North_Carolina" | d.text
d.vect map=zipcodes_wake where="ZIPNAME = ’RALEIGH’"
echo "https://en.wikipedia.org/wiki/Cary,_North_Carolina" | d.text
d.vect map=zipcodes_wake where="ZIPNAME = ’CARY’" fill_color=180:200:210
Stop the driver once all polygon have been displayed. This will create a file named ’htmlmap’ in your
current directory:
d.mon stop=html
You will also want to create an image for your image map. Use the PNG driver and other utilities to
create .gif or .jpg files. ThefollowingexampleissomewhatoutofdateandreferstooptionsavailableinGRASS5.
# using previous GRASS_RENDER_WIDTH & GRASS_RENDER_HEIGHT
d.mon start=png
d.rast map=terrain
d.vect map=area51 fillcolor=white linecolor=blue
d.vect map=roswell fillcolor=yellow linecolor=blue
d.vect map=states color=green
d.vect map=roads color=black
d.mon stop=png
# make the region the same as the newly created cell for ppm export
g.region save=saved.reg
g.region raster=D_cell
r.out.ppm -q input=D_cell output=alien.ppm
# use the netpbm utilities to create a gif (quantize if needed)
ppmquant 128 <alien.ppm | ppmtogif >alien.gif
# assemble some html with the image and the image map
echo ’<html><body><img src="alien.gif" usemap="#map">’ >alien.html
cat htmlmap >>alien.html
echo ’</body></html>’ >>alien.html
# don’t forget to reset your region
g.region region=saved.reg
# take a look and test it out
netscape file:`pwd`/alien.html &
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