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Protocol for geovis render server.  

Commands take the general form of command and arguments using Tcl syntax and are 
terminated by a newline.  Some command arguments expect a Tcl list which can be
sent by enclosing the list in curly braces to prevent the interpreter from 
splitting the list into multiple arguments.  Likewise, strings with spaces 
should be quoted or enclosed in curly braces.  In the documentation below,
arguments are indicated by angle brackets and optional arguments are surrounded
by question marks -- the brackets and question marks are not part of the
protocol and should not be included in argument strings.  The arguments shown 
in angle brackets should be replaced with a string (where there are fixed 
choices this document indicates valid values by separating them with pipe 
symbols), a list in Tcl syntax, or a numeric value.  Boolean arguments can take
the form of 0|1, true|false, or yes|no.  Since the protocol commands are 
executed in a Tcl interpreter, Tcl code such as math expressions in expr 
commands enclosed in square brackets are also allowed.  Since the interpreter
is a "safe" interpreter, some Tcl commands that could cause security issues may 
not be available for use.

When binary data is to be sent, it should follow the newline after a command 
that indicates incoming data including a byte count argument.
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Requests:
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== General dataset, scene and renderer commands ==

camera orient <quatW> <quatX> <quatY> <quatZ>
       Set scene orientation using a quaternion
camera pan <x> <y>
       <x,y> viewport coordinates (window center at 0,0).  Positive x pan
       means pan object to right (camera to left).  Positive y pan means
       pan object down (camera up).  For example a pan of 0.5, 0.5 would
       move the object center to the lower right corner of the window
camera reset <?all?>
       Option all resets orientation/rotation as well as pan/zoom/clip range
camera rotate <x> <y>
       Specify relative rotation in viewport coordinates
camera zoom <z>
       Specify zoom ratio.  z > 1 is a zoom in, z < 1 is zoom out. z = 1
       resets to default.

clientinfo <list>

mouse click <button> <x> <y>
mouse dblclick <button> <x> <y>
mouse drag <button> <x> <y>
mouse motion <x> <y>
mouse release <button> <x> <y>
mouse scroll <direction>

renderer render
         Force a new image to be rendered

screen bgcolor <r> <g> <b>
screen size <width> <height>

map layer add <type> <url> <layerName>
    Add a GDAL image layer from a file or URL
    <type> = image|terrain|model
map layer delete <layerName>
map layer opacity <opacity> <layerName>
map layer move <pos> <layerName>
map layer visible <bool> <layerName>
map load data follows <nbytes>
    Send an .earth file over the wire
map load file <path>
    Load an .earth file from a filesystem mounted on the server
map load url <url>
    Load an .earth file from a network address
map reset <type> <?profile?>
    type = geocentric|projected
    profile = Well known profile string, e.g. 'global-geodetic' (default)
              'global-mercator'

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Replies:
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nv>image -type image -bytes <nbytes>
  <binary RGB data>
nv>dataset coords <x> <y> <z>
nv>ok -token <seqnum>
   Reply indicated commands through <seqnum> (numbered beginning at 1) have been
   processed, but no new image was rendered
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Error Replies:
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nv>viserror -bytes <nbytes>
   <multi-line error string of nbytes>
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