CLUB 100 LIBRARY - 415/939-1246 BBS, 937-5039 NEWSLETTER, 932-8856 VOICE Weather Maps to Go by Alexander B. Trevor 5 September 1983 Weather Maps to Go Page 2 Sometimes the applications for a new device are so obvious that you hardly have to point them out. For example, set a Model-100 in front of a pilot, and it won't take long for him (or her) to realize that this little portable powerhouse could be very handy for pre-flight and in-flight chores. Although there have been other machines that one could tote along in the cockpit, the 100 is the first one with a screen large enough to be useful in flight. Not only can the pilot retrieve flight plans and textual weather information obtained before takeoff from an information service (or entered manually), but the 100 is capable of pretty decent graphics - a capability that can be used to display weather radar maps. Graphical weather maps are available from a number of sources, but one of the least expensive ways to obtain maps that are easily displayed on the Model 100 is to download the Vidtex (tm) Radar Maps from CompuServe. To do this, one must have a CompuServe Information Service account, and at least 16K of memory. The downloaded maps can consume up to 4K. The maps are transmitted in "run length encoding", which reduces transmission time as well as minimizing the amount of RAM required to store them. However, without a program to decode the run length encoding, the maps make about as much sense as the listing of a .CO file. Two different graphic resolutions are used: "high resolution", which is 256 pixels wide by 192 high, and "medium resolution" (128 x 96). Listing 1 is a program that will plot either high or medium resolution "run length encoded" graphics on the LCD screen. Since the Model 100 screen is only 240 x 64 pixels, high res maps are displayed in three sections, and medium res in two. Weather Maps to Go Page 3 Although anyone interested in weather should find these maps useful, they are of particular interest to aircraft pilots, especially since maps can be displayed at any time (including in flight). They provide a useful reminder of general weather trends, although they are not practical for detailed storm avoidance like true airborne radar, since the data is at least a half hour old, and the resolution is too coarse. Each pixel represents an area 20 x 20 miles. The run-length encoding spans all characters from 30 (decimal) through 511, so eight bit reception must be enabled on your Model 100. This is done by setting the Telcom status to M8N1E. However, CompuServe normally sends 7 bit data with even parity, so you will see some strange garbage if you log in with this setting. The solution is to log on with default status (M7I1E) and change your terminal parameters on CompuServe to set the parity bit to zero. This is easily accomplished by logging on, then typing "GO CIS-9" at the "!" prompt or running DEFALT from the programmers' area. From the DEFALT menu, select 5 (View or Change Current Terminal Parameters). Next, select 8 (Parity) and set it to zero. Finally, exit the DEFALT program and request that changes be effective for future sessions. Before logging in the next time, change your terminal parameters to M8N1E in Telcom. Now when you log on you will see a little bit of strange stuff until you get to the Password: prompt. This is because until you identify yourself, the host computer does not know what terminal parameters you desire. So, the initial "User ID:" prompt is sent with even parity, and those characters with the parity bit set to one (s,I and space) will appear as graphics characters on the 100. Weather Maps to Go Page 4 At this point eveything should appear normal, and you can go to the Aviation Weather section, or directly to the weather maps (GO AWX4). The program will correctly inform you that Telcom is not equipped to display graphics, and they may appear as meaningless characters, but you can ignore this. When you see: CompuServe Vidtex Radar Maps choose 1 - Prepare a map for display. Next, select 2 - Prepare current U.S. radar reports. The system will list the three letter id of each radar site, and the GMT time of the report being collected. After all reports are collected, choose 2 - Display prepared map. You may select any of the maps, but before you press ENTER after your choice, you must first press F2 (Down) and specify the name you wish to use for the downloaded file (MAP1 or whatever). THEN, press ENTER, and you will be treated to several screen fulls of utter garbage, but don't panic! Just wait until you hear a BEEP, then press F2 (Down) to terminate the download, and ENTER to tell the host computer to procede. You can now log off or continue with your on-line session. Once off-line, disconnect and go back to the menu. From here you can run the GRAPHR.BA program. Give it the file name you specified to Telcom, and watch the current weather map appear! An outline of the state boundaries will be drawn with radar "echoes" superimposed on top. "Weak" and "moderate" echos will appear as horizonal shading, while stronger echoes appear solid black. When the screen is full, press any key to see the next section. A design "feature" of the Model 100 will very occasionally cause a map to be partially trashed. For some reason, the Model 100 will not store a delete character (&H7F) in a RAM file Weather Maps to Go Page 5 without some sleight of hand, and one does not get an opportunity to do much magic in TELCOM. The problem can be avoided by writing a special purpose communications program which replaces the delete character with something else. One final remark for those contemplating the use of this program in aircraft: pilots need not be overly concerned about operating a Model 100 in flight. Although the Federal Aviation Regulations (FAR's) saddle the pilot in command with the responsibility of determining whether or not an electronic device (such as the Model 100) will cause harmful interference with your navigation or communications radios, I have found nothing to suggest a problem. My Model 100 has many hours of instrument flight time in my Cherokee Challenger, and I have never noticed any ill effects. I hear the same thing from other pilots who regularly fly 172's, King Airs and such with their little white boxes. For your convenience, this program may be downloaded from the Model 100 SIG XA1 Data Base on CompuServe. The file name is: GRAPHR.100 OK