                                  HTMLMAP driver

                                  Tom Poindexter
                                 tpoindex@nyx.net

  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
at all!)

  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 see GRASS_RENDER_HTMLMAXPOINTS, below.)  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.  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.vect.area	 - draw polygons from a vector file.


    0. Set environment variables:

       GRASS_RENDER_WIDTH=xxx   #if you want another size than the default 640
       export GRASS_RENDER_WIDTH
       GRASS_RENDER_HEIGHT=xxx  #if you want another size than the default 480
       export GRASS_RENDER_WIDTH

       Additionally, HTMLMAP driver recognizes:

       export GRASS_RENDER_HTMLTYPE
       GRASS_RENDER_HTMLTYPE=xxx
            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.

       export GRASS_RENDER_FILE
       GRASS_RENDER_FILE=xxxxxx
	    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.


	export GRASS_RENDER_HTMLMINDIST
	GRASS_RENDER_HTMLMINDIST=xx
	    specifies the minimum distance (in pixels) that a point must
	    change from the previous one to keep in the list of vertices
            for a polygon.  The default is '2', which means that a point's
	    x or y difference from the previous point must change by a number
	    of pixels greater than this value.  This parameters helps
	    to eliminate points closely spaced points.


	export GRASS_RENDER_HTMLMINBBOX
	GRASS_RENDER_HTMLMINBBOX=xx
	    specifies the minimum bounding box dimensions (both width and
	    height) in order to store a polygon.  The default is '2', which
	    means any polygon having bounding box width or height extent
	    of less than 2 pixels will not be output as a clickable area.
            This parameter helps to eliminate clickable areas that are one
	    pixel in height or width, typically a single point or line.


	export GRASS_RENDER_HTMLMAXPOINTS
	GRASS_RENDER_HTMLMAXPOINTS=xx
	    specifies the maximum number of vertices that a polygon can
	    have.  The default is 99.  Some browser can only handle
	    image map polygons of less that 100 vertices.


    1. Start it up.

         # set the environment variables (above) if desired, or use defaults

         d.mon start=HTMLMAP
         d.mon select=HTMLMAP

    2. Display text strings (href's) and area polygons:

         echo "http://www.no-such-place.net/area51/" | d.text
	 d.vect.area map=area51
         echo "http://www.roswell-nm.net/little/green/men.html" | d.text
	 d.vect.area map=roswell

    3. When done displaying stuff to HTMLMAP driver, use

         d.mon stop=HTMLMAP

       This will write the image map file file. A new file called 'htmlmap'
       (or whatever you specified with GRASS_RENDER_FILE) 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_RENDER_WIDTH & GRASS_RENDER_HEIGHT
         d.mon start=CELL
         d.mon select=CELL
         d.rast map=terrain
         d.vect.area map=area51  fillcolor=white  linecolor=blue
         d.vect.area map=roswell fillcolor=yellow linecolor=blue
         d.vect map=states  color=green
         d.vect map=roads   color=blue
         d.mon stop=CELL
         # make the region the same as the newly created cell for ppm export
         g.pushregion.sh  # or 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.popregion.sh   # or g.region region=saved.reg
	 # take a look and test it out
	 netscape file:`pwd`/alien.html &



  Building the HTMLMAP driver:

    Change to the HTMLMAP directory, and make it:

	cd src/display/devices/HTMLMAP
	gmake5

    If all goes well, the HTMLMAP driver will be compiled and moved into
    your device driver directory ($GISBASE/driver) and "etc/monitorcap"
    will be modified.


  Other:

    Don't forget to add the HTMLMAP driver in your monitorcap file!
    Your monitorcap file exists as $GISBASE/etc/monitorcap.

        HTMLMAP:driver/HTMLMAP:Create HTML Image Map: \
             /usr/local/grass43/dev/fifo.9a /usr/local/grass43/dev/fifo.9b \
             ::any terminal

    Note: This job will be done by the Gmakefile.

    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

	http://www.ecse.rpi.edu/Homepages/wrf/
	http://www.ecse.rpi.edu/Homepages/wrf/research/geom/pnpoly.html


    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"/' <htmlmap >foomap.html


-----------------------------
http://www.nyx.net/~tpoindex/grass-stuff/
