GPS module - time calculation incorrect?

[chvvkumar]

Module:
https://github.com/AllskyTeam/allsky-modules/blob/dc720ce6f86af2aa6ae895df21c04744a705bf0b/allsky_pigps/allsky_pigps.py

I am using the GPS module with a Sparkfun NEO-M9N USB GPS module.

I noticed that the local time calculated using GPS is incorrect for my location:

(venv) pi@allskypi5:~/tmp $ date
Fri May 16 17:55:44 CDT 2025

2025-05-16T17:54:18.052810-05:00 allskypi5 allskperiodic[171999]: INFO: --------------- Running Module allsky_pigps ---------------
2025-05-16T17:54:18.052824-05:00 allskypi5 allskperiodic[171999]: INFO: Time sync active False, time synched False
2025-05-16T17:54:18.052838-05:00 allskypi5 allskperiodic[171999]: INFO: GPS UTC time 2025-05-16 22:54:17. Local time 2025-05-17 03:54:17. TZ Diff -5.0
2025-05-16T17:54:18.052853-05:00 allskypi5 allskperiodic[171999]: INFO: Lat Lon - 

From doing a bit of reading, it appears that while the script correctly identifies timezone offset as -5.0 hours (CDT), it's subtracting this value from UTC when it should be adding it:

• Current system time: 17:55:44 CDT 2025
• GPS UTC time: 22:54:17 (which is correct UTC time)
• Script's calculated "local time": 03:54:17
• TZ Diff (offset): -5.0

local = utc - timedelta(hours=offset)

Since my offset is -5.0, this calculation becomes:
local = utc - timedelta(hours=-5.0)
which is effectively:
local = utc + timedelta(hours=5.0)

This adds 5 hours to UTC instead of subtracting 5 hours, resulting in a time that's off by 10 hours from my local actual local time (5 hours in the wrong direction from UTC).

Should line 271 be changed like so?

allsky-modules/allsky_pigps/allsky_pigps.py

Line 265 in dc720ce

local = utc - timedelta(hours=offset)

from:
local = utc - timedelta(hours=offset)
to:
local = utc + timedelta(hours=offset)

But this would break the calculation for time zones ahead of the UTC.

Please let me know if my assumption above is incorrect, I am not too well versed with working with time and date values.

[Alex-developer]

Thanks of the report - I will have a look