CWOP air prerssure data

[nking]

I have just setup my WH1081 to send data to APRS and have noticed that the pressure reported is 1013.7 which should be absolute adjusted by elevation (120ft or 36.5M). WH1081 Absolute reads 1009.5 my relative is 1015.9 so I guess from this the WH1081 is not very accurate for absolute and therefore the adjusted figure sent to aprs is useless. Have I understood this situation correctly and is there a workaround. I haven't played with the offsets as I didn't want to corrupt my data logging in Cumulus

I hope this all makes sense and hope someone can clarify for me - Thanks

[steve]

Yes, your reading of the situation is correct. I changed the way Cumulus does pressure for CWOP so that it correctly sends Altimeter Pressure rather than MSLP. It was really Davis users that needed the change because the Davis stations calculate MSLP properly, whereas other stations clearly do not. For consistency, I changed the code for all station types. Since then, I've been mulling over whether I did the right thing, precisely for the reason you have highlighted; the Fine Offset stations are clearly not very accurate at measuring absolute pressure, and there is no way to correct the calculated altimeter pressure other than fudging your altitude.

I think I will change the code (back) so that Cumulus sends the standard relative/sea-level pressure to CWOP for non-Davis stations.

[nking]

Thanks for clarifying the point. I am conscious of the difficulty that exists with your time and I for one would feel happy if you said NO to making any changes to C1 (unless it’s a really critical issue that stops C1 running) and that you will try to incorporate this into C2. This would then ease the conflict that exists and help you focus your energy to delivering C2…… just a thought

[steve]

Thanks for clarifying the point. I am conscious of the difficulty that exists with your time and I for one would feel happy if you said NO to making any changes to C1 (unless it’s a really critical issue that stops C1 running) and that you will try to incorporate this into C2. This would then ease the conflict that exists and help you focus your energy to delivering C2…… just a thought

Well... you could say it's a bug, really, and I should fix bugs.