NAME
HTMLMAP driver - driver to create HTML image maps.
(drivers)
DESCRIPTION
The HTMLMAP driver allows 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 GRASS display commands that require the MOUSE will not work
correctly (or at all!)
Polygons can at most have 100 vertices (this limit imposed by HTML image map
formats, see GRASS_HTMLMAXPOINTS below.) The driver will attempt to
trim polygons that have more that 100
vertices by removing vertices with the least amount of angle to the next
vertice. Also, any polygon that is entirely bounded by another polygon will be
discarded.
Text written to the driver before polygons are used as the HREF tag for all
subsequent polygons written. All polygons that exist in a vector map 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.vect
- draw polygons from a vector map.
USAGE
Environment variables
Several environment variables affect the operation
of HTMLMAP.
- 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_HTMLTYPE=type
the type of image mape 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 ( url x1 y1 x2 y2
..... ), suitable for conversion to CERN server format, or any other
format with user supplied conversion program.
- GRASS_HTMLFILE=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.
Any existing file of the same name is overwritten without
warning.
- GRASS_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_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_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.
Typical usage
- Start up the driver
- Display text strings (HREF's) and polygons
echo "http://www.no-such-place.net/area51/" | d.text
d.vect map=area51
echo "http://www.roswell-nm.net/little/green/men.html" | d.text
d.vect map=roswell
- Stop the driver when all polygon have been displayed. This will cause a file
named 'htmlmap' to be created in your current directory.
- 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.
The following example is somewhat out of date and refers to options
available in GRASS 5.
# using previous GRASS_WIDTH & GRASS_HEIGHT
d.mon start=PNG
d.mon select=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 &
NOTES
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 and 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"/' < htmlmap > foomap.html
SEE ALSO
Display drivers
PNG driver,
PostScript driver,
XDRIVER
d.mon,
d.text,
d.vect
Last changed: $Date$