1htmldriver(1)               GRASS GIS User's Manual              htmldriver(1)
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HTML DISPLAY DRIVER

6       HTML display driver to create HTML image maps.
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DESCRIPTION

9       The  HTML driver allows the generation of HTML image maps for area vec‐
10       tor data. HTML image maps are used in conjunction with images  to  pro‐
11       vide  unique  URL  targets for different portions of an image. The HTML
12       driver can create both client-side image maps embedded into HTML files,
13       or server-side image maps used by web server software.
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15       Polygons  can at most have 100 vertices (this limit imposed by HTML im‐
16       age map formats, see GRASS_RENDER_HTMLMAXPOINTS below.) The driver will
17       attempt  to  trim polygons that have more that 100 vertices by removing
18       vertices with the least amount of angle to the next vertice. Also,  any
19       polygon that is entirely bounded by another polygon will be discarded.
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21       Text written to the driver before polygons are used as the HREF tag for
22       all subsequent polygons written. All polygons that exist  in  a  vector
23       map will have the same HREF tag.
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25       The  only  GRASS  display commands that should be used with this driver
26       are:
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28d.text - pass href information for resulting image maps.
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30d.vect - draw polygons from a vector map.
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USAGE

33   Environment variables
34       The HTML driver can be enabled by setting GRASS_RENDER_IMMEDIATE  vari‐
35       able, eg.
36       export GRASS_RENDER_IMMEDIATE=html
37       Several environment variables affect the operation of the HTML driver:
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39GRASS_RENDER_WIDTH=xxx
40               the width of the image map (default is 640).
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42GRASS_RENDER_HEIGHT=yyy
43               the height of the image map (default is 480).
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45GRASS_RENDER_HTMLTYPE=type
46               type of image mape to create (default is CLIENT):
47               CLIENT    Netscape/IE client-side image map (NAME="map").
48               APACHE    Apache/NCSA server-side image map.
49               RAW           Raw  url  and polygon vertices (url  x1 
50               y1  x2  y2  .....), suitable for conversion to  CERN  server
51               format,  or any other format with user supplied conversion pro‐
52               gram.
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54GRASS_RENDER_FILE=filename
55               specifies the resulting file to store the html image  map,  de‐
56               fault is htmlmap. Files without absolute path names are written
57               in the current directory where the driver was started.
58               Any existing file of the same name is overwritten without warn‐
59               ing.
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61GRASS_RENDER_HTMLMINDIST=n
62               specifies  the  minimum  distance  in  pixels that a point must
63               change from the previous point to keep in the list of  vertices
64               for  a polygon.  The default is 2, which means that a point’s x
65               and y difference from the previous point must change by a  num‐
66               ber of pixels greater than this value.  This parameter helps to
67               eliminate closely spaced points.
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69GRASS_RENDER_HTMLMINBBOX=n
70               specifies the minimum bounding box dimensions to record a poly‐
71               gon  as a clickable area.  The default is 2, which means that a
72               polygon with a bounding box of less than this value is not  in‐
73               cluded.  This  parameter helps to eliminate polygons than are a
74               point or line.
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76GRASS_RENDER_HTMLMAXPOINTS=n
77               specifies the maximum number of vertices included  in  a  poly‐
78               gon’s  clickable  area.   The  default is 99. Some browsers can
79               only accommodate polygons of 100 vertices or less. The  HTMLMAP
80               driver automatically ensures that a polygon is closed by making
81               the last point the same as the first point.
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83   Example
84       Start up the driver
85       g.region vector=zipcodes_wake
86       d.mon start=html
87       Display text strings (HREF’s) and polygons
88       echo "https://en.wikipedia.org/wiki/Raleigh,_North_Carolina" | d.text
89       d.vect map=zipcodes_wake where="ZIPNAME = ’RALEIGH’"
90       echo "https://en.wikipedia.org/wiki/Cary,_North_Carolina" | d.text
91       d.vect map=zipcodes_wake where="ZIPNAME = ’CARY’" fill_color=180:200:210
92       Stop the driver once all polygon have been displayed. This will  create
93       a file named ’htmlmap’ in your current directory:
94       d.mon stop=html
95       You  will  also want to create an image for your image map. Use the PNG
96       driver and other utilities to create .gif or .jpg files.  The following
97       example  is  somewhat  out  of  date and refers to options available in
98       GRASS 5.
99       # using previous GRASS_RENDER_WIDTH & GRASS_RENDER_HEIGHT
100       d.mon start=png
101       d.rast map=terrain
102       d.vect map=area51  fillcolor=white  linecolor=blue
103       d.vect map=roswell fillcolor=yellow linecolor=blue
104       d.vect map=states  color=green
105       d.vect map=roads   color=black
106       d.mon stop=png
107       # make the region the same as the newly created cell for ppm export
108       g.region save=saved.reg
109       g.region raster=D_cell
110       r.out.ppm -q input=D_cell output=alien.ppm
111       # use the netpbm utilities to create a gif (quantize if needed)
112       ppmquant 128 <alien.ppm |  ppmtogif >alien.gif
113       # assemble some html with the image and the image map
114       echo ’<html><body><img src="alien.gif" usemap="#map">’ >alien.html
115       cat htmlmap                                           >>alien.html
116       echo ’</body></html>’                                 >>alien.html
117       # don’t forget to reset your region
118       g.region region=saved.reg
119       # take a look and test it out
120       netscape file:`pwd`/alien.html &
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NOTES

123       HTML was adapted from the CELL driver in GRASS  4.3.   Point-in-polygon
124       test code was lifted from Randolph Franklin’s web page, see
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126http://www.ecse.rpi.edu/Homepages/wrf/
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128http://www.ecse.rpi.edu/Homepages/wrf/research/geom/pnpoly.html
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130       If  you create an HTML file with two or more images and image maps, you
131       will need to edit the map names. The HTML driver creates its  map  with
132       the name map. A small sed script can easily change the map name:
133       sed -e ’s/NAME="map"/NAME="foomap"/’ < htmlmap > foomap.html
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SEE ALSO

136        Cairo driver, PNG driver, HTML driver, variables
137       d.rast, d.vect, d.mon, d.erase, d.redraw
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AUTHOR

140       Glynn Clements
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142       Main index | Topics index | Keywords index | Graphical index | Full in‐
143       dex
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145       © 2003-2023 GRASS Development Team, GRASS GIS 8.2.1 Reference Manual
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149GRASS 8.2.1                                                      htmldriver(1)
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