Tom Poindexter, March, 2000
This display driver is to allow the generation of HTML image maps for
area vector data. HTML image maps are used in conjunction with images
to provide unique URL targets for different portions of an image. The HTMLMAP
driver can create both client-side image maps embedded into HTML files, or
server-side image maps used by web server software.
Note that commands that require the MOUSE will NOT work correctly (or
Polygons can at most have 100 vertices (this limit imposed by HTML image map
formats.) The driver will attempt to trim polygons that have more that 100
vertices. Also, any polygon that is entirely bounded by another polygon will
Text written to the driver before polygons are used as the HREF tag for
all subsequent polygons written. It is intended that all polygons
that exists in a vector file will have the same HREF tag.
The only GRASS display commands that should be used with this driver are:
d.text - pass href information for resulting image maps.
d.area - draw polygons from a vector file.
0. Set environment variables:
GRASS_WIDTH=xxx #if you want another size than the default 640
GRASS_HEIGHT=xxx #if you want another size than the default 480
Additionally, HTMLMAP driver recognizes:
specifies the type of Html map to create:
CLIENT - Netscape client-side image map (default). (NAME="map")
APACHE - Apache/NCSA server-side image map
RAW - Raw url and polygon vertices ("url x1 y1 x2 y2 .....")
suitable for conversion to CERN server format, or
any other format with user supplied conversion program.
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.
Any existing file is overwritten without warning.
1. Start it up.
# set the environment variables (above) if desired, or use defaults
2. Display text strings (href's) and area polygons:
echo "http://www.no-such-place.net/area51/" | d.text
echo "http://www.roswell-nm.net/little/green/men.html" | d.text
3. When done displaying stuff to HTMLMAP driver, use
This will write the image map file file. A new file called 'htmlmap'
(or whatever you specified with GRASS_HTMLFILE) will be created
in your current directory.
4. In practice, you'll want to create gif/jpg/png images that correspond
with your newly created image map:
# using previous GRASS_WIDTH & GRASS_HEIGHT
d.area map=area51 fillcolor=white linecolor=blue
d.area map=roswell fillcolor=yellow linecolor=blue
d.vect map=states color=green
d.vect map=roads color=blue
# make the region the same as the newly created cell for ppm export
g.pushregion.sh # or g.region save=saved.reg
r.out.ppm -q input=D_cell output=alien.ppm
# use the netpbm utilities to create a gif (quantize if needed)
ppmquant 128 alien.gif
# assemble some html with the image and the image map
echo '' >alien.html
cat htmlmap >>alien.html
echo '' >>alien.html
# don't forget to reset your region
g.popregion.sh # or g.region region=saved.reg
# take a look and test it out
netscape file:`pwd`/alien.html &
Building the HTMLMAP driver:
For best results, unpack HTMLMAP into your top level GRASS 4.3 source
directory. This will create a new directory and source files in
Change to that directory, and make it.
If all goes well, the HTMLMAP driver will be compiled and moved into
your device driver directory ($GISBASE/driver).
The makefile will add a monitorcap entry for you (thanks Markus Neteler.)
HTMLMAP was adapted from the CELL driver in GRASS 4.3. Point-in-
polygon-test code was lifted from Randolph Franklin's web page, see
If you create an HTML file with two or more images & image maps, you
will need to edit the map names. The HTMLMAP driver creates its map
with the name 'map'. A small sed script can easily change the map name:
sed -e 's/NAME="map"/NAME="foomap"/' foomap.html