1htmldriver(1)                 Grass 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
16       image map formats, see GRASS_RENDER_HTMLMAXPOINTS  below.)  The  driver
17       will  attempt  to  trim  polygons  that  have more that 100 vertices by
18       removing vertices with the least amount of angle to the  next  vertice.
19       Also,  any  polygon that is entirely bounded by another polygon will be
20       discarded.
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22       Text written to the driver before polygons are used as the HREF tag for
23       all  subsequent  polygons  written. All polygons that exist in a vector
24       map will have the same HREF tag.
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26       The only GRASS display commands that should be used  with  this  driver
27       are:
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29           ·   d.text - pass href information for resulting image maps.
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31           ·   d.vect - draw polygons from a vector map.
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USAGE

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

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

137        Cairo driver, PNG driver, HTML driver, variables
138       d.rast, d.vect, d.mon, d.erase, d.redraw
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140       Main index | Topics index | Keywords index |  Graphical  index  |  Full
141       index
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143       © 2003-2019 GRASS Development Team, GRASS GIS 7.8.2 Reference Manual
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147GRASS 7.8.2                                                      htmldriver(1)
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