readme.design

The OpenGPSRec receiver software runs on the real time operating system RTAI-Linux. It compiles with

DESCRIPTION: 	This file discusses the design of gpsplot, a OpenGL plotting
				tool used to plot data that OpenGPS produces.

AUTHOR:		Stephan Esterhuizen

DATE:		24 July 2003

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FEATURES/LIMITATIONS
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gpsplot will be able to support the following features:

 - time plot of IE,QE,IL,QL overlayed on each other
 - time plot of any combination of I/Q dumps, including
 		+ Power Late
		+ Power Early
		+ Power Prompt

 - polar plot of any two I/Q dumps
 - Different colours for overlayed graphs
 - Only graphs of some magnitude/units can be overlayed
 - Only one OpenGL window per gpsplot instance is possible

Data communication is via ring buffer containing elements CHAN_INFO

offset     size         quantity

  0        long         length of buffer in units size( CHAN_INFO)
  4        long         most recently written element 
  8   size( CHAN_INFO)  array of elements

total length: N * size( CHAN_INFO) + 8 bytes

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GRAPH FEATURES
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In order to sustain the above features, the OpenGL graphing library must


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GRAPH FUNCTIONS
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Polar
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The polar plot graphing utility will have the following function calls

 - polarPlotDraw() : This gets called by the idle OpenGL function. This
 					 function will draw all the points in its data array

 - polarPlotAdd(x,y,colour) : Add point (x,y) to the polar plot's data array.

 - x,y,index = polarPlotGet(index) : Returns the x,y coordinates and colour
 									 of pixel at 'index'. index=0 is the newest
									 pixel, while index=MAX_POLAR_BUF is the
									 oldest x,y coordinate

 - polarPlotXLabel(label) : change the x label to 'label'

 - polarPlotYLabel(label) : change the y label to 'label'

The data array for polarPlot will be a circular buffer