	     Some Frequently Asked Questions about LXGPS

Q. I can't get LXGPS to talk to my GPS.  What do I do?

A. First make sure that your serial port is enabled.  In the built-in
   Setup app, make sure 'Enable Com1 Port in DOS' is checked.  Also,
   you may have to use the d:\bin\serctl /w command at the DOS prompt.
   If you're using BUDDY, make sure it turns on the serial port (++
   from FILER).

   See if you can get output from your GPS using the built-in DataComm
   application.

   If you launch LXGPS from the App Manager, make sure you've got an
   upside-down exclamation point in the comments field (Fn FILER) to
   ensure the serial port isn't getting messed up by the System
   Manager.

Q. Where do I get maps for LXGPS?

A. I've been using screen captures from Delorme's Street Atlas (which
   came with the Tripmate GPS).  For the US map that comes with LXGPS,
   I used the Xeroc PARC map viewer (http://mapweb.parc.xerox.com/map).
   There are several other sources of maps on the Web.  Here are a
   few:

	www.mapblast.com
	tiger.census.gov
	www.delorme.com

   To use a map with LXGPS it must be in 1 bit-per-pixel PCX format.
   Before LXGPS can use it, you must calibrate it.  To calibrate a
   map, you need to know the latitude and longitude of two points on
   the map.  Also the map must be oriented with North up, West left
   and the horizontal and vertical axes must be linear.

Q. How can I convert maps to 1 bit-per-pixel?

A. Most image editing/paint programs will allow you to convert an
   image to 1 bit-per-pixel.  I've had good luck with Paint Shop Pro.
   Your local web archive should have a good selection of programs.
   Try www.download.com for a start.  If you want to do the conversion
   on the palmtop, try LXPIC (http://home.t-online.de/home/stefan.peichl/).

Q. How come the altitude isn't correct?

A. Your tax dollars at work :-).  The GPS signal is fuzzed by the
   government.  This is known as "selective availablity".  From the
   Delorme web page:

	Your accuracy will also depend upon your level of clearance
	with the US Department of Defense. There are two available
	radio signals that receivers can use: the Standard Positioning
	Service (SPS) for civilians and the Precise Positioning
	Service (PPS) for military and authorized personnel.

	The most significant cause of error in positioning is the
	deliberate effort by the Department of Defense to decrease the
	accuracy of user systems. Selective Availability (SA) is the
	purposeful degradation of the information broadcast by the
	satellites. SA affects the accuracy of the SPS, not the
	PPS. With SA, your SPS system will be accurate to within at
	least 328 feet (100 meters) horizontally and 512 feet (156
	meters) vertically 95 percent of the time.

	In addition to the routine Selective Availability that
	degrades the accuracy of user systems, the Department of
	Defense occasionally jams and otherwise makes GPS useless to
	civilians on a short-term basis. The US government operates
	the Global Positioning System and is responsible for its
	accuracy and maintenance.

Q. Why is north at the bottom of the satellite display?

A. This is to make it easier to visualize the positions of the satellites
   in the sky.  The display represents how the sky appears if you stand
   facing north and look up.


$Id: faq,v 1.4 1997/11/19 01:50:09 greg Exp $

