Compression

Compression
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Note that the following is done at object creation to ensure proper formatting:

	private final DecimalFormatSymbols dfs = new DecimalFormatSymbols();
	
	TNCparser()
	{
		dfs.setDecimalSeparator('.');
		dfs.setZeroDigit('0');
	}

This code converts compressed format to standard format.

	protected String convertCompressed(String theString, Report theReport)
	{
		// theString is the compressed part of the packet
		if (!theReport.toField.startsWith("AP"))
			return "NOTVALIDPACKET";  // Will cause lat parse to bomb
		// Parse Icon for later adjustment
		char symID = theString.charAt(0);
		// Adjust the icon for plain text
		if ((symID >= 'a') && (symID <= 'j')) symID = (char)(symID - 49);
		char symCode = theString.charAt(9);
		// Compute lat/long
		Double lat = new Double(90.0-((((((((theString.charAt(1)-33)*91.0)+(theString.charAt(2)-33))*91.0)+(theString.charAt(3)-33))*91.0)+(theString.charAt(4)-33))/380926.0));
		Double longitude = new Double(-180.0+((((((((theString.charAt(5)-33)*91.0)+(theString.charAt(6)-33))*91.0)+(theString.charAt(7)-33))*91.0)+(theString.charAt(8)-33))/190463.0));
		// Compute course/speed bytes
		String cs = "";
		if (theString.charAt(10) == ' ')
		{
			if (symCode == '_' || symCode == 'W')
				cs = "000/000";  // Compressed Weather Report
		}
		else
		{
			// c/s represents something
			if (((theString.charAt(12) - 33) & 0x18) == 0x10)
			{
				theReport.reportType = "GGA";
				theReport.altitude = (int)Math.round(Math.pow(1.002,(theString.charAt(10)-33)*91+(theString.charAt(11)-33)));
			}
			else if (theString.charAt(10) == '{')
			{
				// Radio Range
				DecimalFormat df = new DecimalFormat("0000", dfs);
				cs = "RNG" + df.format(2.0*Math.pow(1.08,theString.charAt(11)-33));
			}
			else
			{
				// Course/Speed
				DecimalFormat df = new DecimalFormat("000", dfs);
				// Compressed speed is in Knots
				cs = df.format((theString.charAt(10)-33)*4);
				if (cs.equals("000")) cs = "360";
				cs += "/" + df.format(Math.pow(1.08,theString.charAt(11)-33)-1.0);
			}
			if (((theString.charAt(12)-33) & 0x18) == 0x18)
				theReport.reportType = "RMC";
			else if (((theString.charAt(12)-33) & 0x18) == 0x08)
				theReport.reportType = "GLL";
		}
		// Create the strings for replacing the compressed info
		DecimalFormat latf = new DecimalFormat("00", dfs);
		DecimalFormat longf = new DecimalFormat("000", dfs);
		DecimalFormat minf = new DecimalFormat("00.00", dfs);
		String lats = latf.format(Math.abs(lat.intValue())) + minf.format(Math.abs((lat.doubleValue() - lat.intValue())*60.0));
		if (lat.doubleValue() >= 0.0) lats = lats + "N";
		else lats = lats + "S";
		String longs = longf.format(Math.abs(longitude.intValue())) + minf.format( Math.abs((longitude.doubleValue() - longitude.intValue())*60.0));
		if (longitude.doubleValue() < 0.0) longs = longs + "W";
		else longs = longs + "E";
		// Replaced the compressed data with plain text
		if (theString.length() > 13)
			cs += theString.substring(13);
		return lats + symID + longs + symCode + cs;
	}

APRS is a registered trademark of APRS Software and Bob Bruninga, WB4APR.