Author Topic: 255 mph on GRLevel3 and raw APRS data  (Read 508 times)

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Offline miraculon

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255 mph on GRLevel3 and raw APRS data
« on: October 10, 2018, 09:46:12 AM »
I was looking at the GRLevel3 map to see what is going on with hurricane Michael this morning.

Conspicuous on the map was a a pennant with four long barbs and a short one for CWOP station FW2930. Although the wind barb is showing NNE, floating over the station shows "Unknown at 255 mph".

I checked CWOP and looked at the raw packets.

Quote
FW2930>APRS,TCPXX*,qAX,CWOP-4:@090802z3025.67N/08635.49W_072/022t077h96b1005421BTSTWx Upload 2.3.0
FW2930>APRS,TCPXX*,qAX,CWOP-2:@091332z3025.67N/08635.49W_053/023t077h96b1005210BTSTWx Upload 2.3.0
FW2930>APRS,TCPXX*,qAX,CWOP-7:@091902z3025.67N/08635.49W_073/022t077h96b1005150BTSTWx Upload 2.3.0
FW2930>APRS,TCPXX*,qAX,CWOP-2:@092432z3025.67N/08635.49W_076/020t076h95b1004943BTSTWx Upload 2.3.0
FW2930>APRS,TCPXX*,qAX,CWOP-3:@093002z3025.67N/08635.49W_076/020t076h95b1004983BTSTWx Upload 2.3.0

FW2930>APRS,TCPXX*,qAX,CWOP-7:@125332z3025.67N/08635.49W_32767/255t3277h255b1000359BTSTWx Upload 2.3.0
FW2930>APRS,TCPXX*,qAX,CWOP-7:@125902z3025.67N/08635.49W_32767/255t3277h255b1000299BTSTWx Upload 2.3.0
FW2930>APRS,TCPXX*,qAX,CWOP-2:@130432z3025.67N/08635.49W_32767/255t3277h255b1000029BTSTWx Upload 2.3.0
FW2930>APRS,TCPXX*,qAX,CWOP-6:@131002z3025.67N/08635.49W_32767/255t3277h255b999959BTSTWx Upload 2.3.0
FW2930>APRS,TCPXX*,qAX,CWOP-2:@131532z3025.67N/08635.49W_32767/255t3277h255b999889BTSTWx Upload 2.3.0


The raw weather data for this station (1st)does not seem to have the problem, but the APRS packets (2nd) do. The raw packet parsing info that I found online seems to not reflect everything in these strings.

Apparently CWOP raw data is a little different and does not suffer from this issue present in the raw APRS data.

Ironically, I have seen the "255 mph" problem on DW5664 which is a Davis station that NWS Gaylord has installed. (not happening currently)

Anyone have any ideas or explanation for this? The "255 mph" sticks out like the proverbial sore thumb on the GRLevel3 map.

Interestingly, looking at this station on aprs.fi looks normal with no sign of the "255"...

Greg H.

« Last Edit: October 13, 2018, 02:22:52 PM by miraculon »


Blitzortung Stations #706 and #1682
CoCoRaHS: MI-PI-1
CWOP: CW4114 and KE8DAF-13
WU: KMIROGER7
Amateur Radio Callsign: KE8DAF

Offline galfert

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Re: 255 mph on GRLevel3 and raw APRS data
« Reply #1 on: October 12, 2018, 09:43:05 AM »
I think the simple explanation is that the software uploading has bugs. Not only are the gusts reporting as 255 but the regular wind speed is off the chart. 255 is probably a stack overflow error (technical term for when a calculation exceeds the working memory for the program or defined variable). The highest number possible with 8 bits of memory is 255. What is most likely happening is that erroneously calculated gust is probably much higher than the already crazy high wind speed. Then a stack overflow happens and the software only sees the last 8 bits that are full, all ones (11111111) which = 255. Or it could be that the program was coded to output 255 as an error code when hardware malfunctions.

The fact that aprs.fi looks good just means that they are ignoring badly formated packets. So they are only keeping and showing whatever data is good and connecting the dots between good packets.
« Last Edit: October 12, 2018, 10:12:43 AM by galfert »
WS-2902A | ObserverIP | WeatherBridge (Meteobridge)
WU: KFLWINTE111  |  PWSweather: KFLWINTE111
CWOP: FW3708  |  AWEKAS: 14814
Tele-Pole flag pole is here (not installed yet)

Offline galfert

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Re: 255 mph on GRLevel3 and raw APRS data
« Reply #2 on: October 12, 2018, 10:02:59 AM »
DW5664 is having hardware issues. So it isn't just the wind speed being off but also pressure. I don't suspect a software issue here. There are wind speed numbers higher than 255 so this is purely a hardware problem.

Just look at the barometer jump +50 mb from 1010.1 mb to 1064.2 mb and then back down to 1010.2 mb in just 10 minutes.

DW5664>APRS,TCPXX*,qAX,CWOP7:@120623z4454.45N/08443.13W_272/005g010t036r000p009P002h93b10101L000.DsVP
DW5664>APRS,TCPXX*,qAX,CWOP3:@120628z4454.45N/08443.13W_244/007g013t036r000p009P002h93b10642L000.DsVP
DW5664>APRS,TCPXX*,qAX,CWOP5:@120633z4454.45N/08443.13W_261/007g014t036r000p009P002h93b10102L000.DsVP

« Last Edit: October 12, 2018, 10:17:03 AM by galfert »
WS-2902A | ObserverIP | WeatherBridge (Meteobridge)
WU: KFLWINTE111  |  PWSweather: KFLWINTE111
CWOP: FW3708  |  AWEKAS: 14814
Tele-Pole flag pole is here (not installed yet)

 

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