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-   -   Feedback GDL 39 (https://vansairforce.net/community/showthread.php?t=113023)

aeroaddict 05-18-2014 10:02 AM

Thanks for the response and good to know. I'm also looking at the 796 GDL-39 3D combo to use in the C172 until I finish the 7. My laptop is starting to act up and so was considering a tablet for replacement and in the interim try the Pilot app with a GDL-39 on the tablet. I down loaded the 30 day free trial for my android phone and so far it has worked pretty well (not really good for flying as the screen size is small, but gives a good overview/demonstration of the capabilities).

Thermos 05-18-2014 04:52 PM

I'll second the comments on Pilot's "amplification" of weather returns. I was using it to track weather as I was flying commercial back to Boston from Charleston, SC last week. The intensity of returns didn't seem to match what I was seeing out the window, so I went back to using another iPad radar app that uses what seems to be normal NWS reflectivity scaling. I've been using Pilot quite a bit and am on the verge of buying a GDL-39, but I'd like to see a more accurate depiction of weather.

Perhaps the Garmin folks can explain why their weather rendering is different?

Dave

donaziza 05-19-2014 10:52 AM

Quote:

Originally Posted by donaziza (Post 880603)
I for one, am going to call Garmin Pilot, tomorrow, Monday, and cite this info ( about the weather showing more intense than it actually is) here on VAF and see what they have to say. If it "is" so cranked up, maybe I can get them to tone it down. Will post whatever they tell me tomorrow. Stay tuned

I called Garmin about this Monday morning. Am waiting to hear back from them to see what they say as I also use Garmin Pilot ADS B weather. Will post here whatever they tell me. Might be a couple of days. (Hope this thread doesn't disappear)

g3xpert 05-20-2014 05:54 AM

NEXRAD Data Color Mapping
 
First we want to say that these are all very good questions. There was certainly no decision to alter the weather depiction to look scarier than it is.

We reviewed all available guidance before deciding on how to map NEXRAD radar reflectivity to the colors shown by Garmin Pilot and our other products which display weather.

Some of the best guidance is provided in DO-267A, Minimum Aviation System Performance Standards for FIS-B Data Link and the Aeronautical Information Manual (AIM).

The radar color table used in Garmin Pilot is based on two factors:
  1. DO-267A Appendix H provides guidance for color tables to be applied to weather radar return energy (dBZ) for FIS-B data. Garmin Pilot follows this guidance and consistently applies the color specification to all radar data displayed regardless of source. This is done so that the user can assume the same absolute intensity values based on the color being displayed for all ground based weather products displayed in Garmin Pilot. Note that these colors are the same colors used when displaying airborne radar.

  2. There is a direct correlation between ATC terminology and the base color palette used in Garmin Pilot. Green shades correspond to ?Light"; Yellow shades correspond to ?Moderate?; Red shades correspond to ?Heavy?; Magenta shades correspond to ?Extreme?.
Section 7 of the AIM identifies ?MODERATE? precipitation (as communicated by ATC) as precipitation which results in a reflectivity of 30 to 40 dBZ. 30 to 40 dBZ maps to the color yellow in DO-267A, so we felt it important to show precipitation in the ?MODERATE? range as yellow. Some internet sources of weather will map precipitation at the low end of this range to dark green.

We also notice that it is not uncommon for FIS-B NEXRAD data to show more red (heavy precipitation) data than shown in SXM weather data, but again we use the same color mapping regardless of data source and will show red when the data indicates it should be represented in this manner.

Thanks,
Steve

BCP Boys 05-20-2014 06:47 AM

Thanks for the update
 
Steve,
Thanks for the update on this. It sounds like this was done based on a lot of research and was intentionally done this way. Personally, as long as I know what to expect and what the colors mean I think it will work out fine. The issue was that the "normal" colors that I'm used to seeing from XM or FIS-B on other Apps didn't match. My assumption and expectation was that these colors were some what universal. Similar to watching the news and seeing Radar images on one channel then flipping the channel to another news cast and seeing the same images (or colors) on another channel. But like I said as long as I know what the color representation stands for it should be fine . . . it's the data that it represents that matters not the pretty colors :D.

Just one more question/clarification Steve: Are these colors only used on the App? So on other Garmin products like the 796 or even the G3X system should we expect these same colors or is this just for the Pilot App?

g3xpert 05-20-2014 08:20 AM

Quote:

Originally Posted by BCP Boys (Post 881248)
Just one more question/clarification Steve: Are these colors only used on the App? So on other Garmin products like the 796 or even the G3X system should we expect these same colors or is this just for the Pilot App?

Hello AB,

Yes, this method of assigning colors to NEXRAD data is consistently applied across Garmin products including the Aera 796 and G3X.

Our certified products are actually required to follow DO-267A guidance as part of receiving one or more related TSOs.

Thanks,
Steve

BCP Boys 05-20-2014 08:59 AM

Excellent ! Thanks Steve.

donaziza 05-20-2014 09:32 AM

Well---Y'all heard the man. Next thing to do, instead of just a few RV er's with Garmin Pilot installed, is have an army of RV er's with Garmin Pilot (installed) go out in real world conditions and report back here. That's what I'm going to do (as soon as I heal up and can fly again)

g3xpert 05-20-2014 09:42 AM

I can hear it now.

Center, this is RV12WX. How would you characterize that precip at my 12 o'clock. Light, Moderate, or Heavy? :)

Steve

N15JB 05-20-2014 12:07 PM

Quote:

Originally Posted by g3xpert (Post 881305)
I can hear it now.

Center, this is RV12WX. How would you characterize that precip at my 12 o'clock. Light, Moderate, or Heavy? :)

Steve

Interesting that you should mention this. It is actually the opposite, at least in my area. I attended last night a 2 hour Q & A session with controllers from DEN, APA, COS, Ctr and tracon. The DEN controller commented that any GA aircraft with on board weather, including portables, had a better wx. display then they did in the tower. They commonly call aircraft in the air and on the ground to see what they are reporting. DEN is the 3rd or 4th busiest airport in the country and relatively new, so I assume( I know, I know) that the equipment isn't any better elsewhere.

I may have heard this incorrectly, but I believe they also said that their ability to see light precip is so poor that they don't even report it anymore.

It was a very helpful meeting.

Jim Berry
RV-10


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