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Why does IFD only use 4 colors when painting wx

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310pilot View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 310pilot Quote  Post ReplyReply Direct Link To This Post Topic: Why does IFD only use 4 colors when painting wx
    Posted: 15 Jul 2020 at 2:31pm
The IFD sells us short with the colors(lack thereof) it uses to paint weather. Other units use different shades of green and yellow for example to paint a better picture of the weather intensity.
This results in the IFD painting a worse picture then Foreflight for example. When the IFD paints yellow , ForeFlight weather will be green, the IFDs red is Foreflights yellow. With a color palette as robust as the one available on the IFD it seems like an easy fix to incorporate lighter and darker shades of each color to give us a more accurate picture of the weather and at the same time more closely matching some of the other weather displays.


Edited by 310pilot - 15 Jul 2020 at 2:37pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote HenryM Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2020 at 5:10pm
The colors displayed depend largely on the source of the weather data. Foreflight has a document called "Foreflight Weather Legend" that shows the differences: http://cloudfront.foreflight.com/docs/ff/9.6/v9.6%20-%20foreflight%20weather%20legends%20optimized.pdf

The IFD is likely showing ADS-B weather, which uses fewer colors than internet weather that you would get if you were using FF on the ground. It is not an IFD issue, but rather a data source issue.

Here's the relevances chart from the legend:



Edited by HenryM - 15 Jul 2020 at 5:12pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 310pilot Quote  Post ReplyReply Direct Link To This Post Posted: 15 Jul 2020 at 6:40pm
Thanks for your reply Henry. I would say that it is very much an IFD issue though. My IFD is displaying XM weather. I fully understand that with Foreflight the colors change slightly depending on the weather source. In all weather sources Foreflight makes use of various shades of the different colors to better show varying intensities. The IFD is fully capable of of displaying more than only 4 colors and very much should be doing so. Also in all instances for all weather sources the IFD will display a more intense echo color than Foreflight.

Edited by 310pilot - 15 Jul 2020 at 6:42pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 310pilot Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2020 at 7:42am
Below is a picture of the same xm weather being displayed differently on two devices (IFD540 & MX20). The MX20 uses different shades of green in this example whereas the IFD only has one green available. Surely if the 1990s MX20 can use multiple colors to depict weather the IFD can as well. Limited to only 4 colors the IFD paints makes this weather look a lot worse than it really is.



 


Edited by 310pilot - 16 Jul 2020 at 7:46am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AviSteve Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2020 at 9:11am
FIS-B weather is displayed according to the requirements of RTCA DO-267A.  I can't post that document, but table 3-2 specifies the colors to be displayed for the various dbz ranges (green, yellow, red, and magenta).  Additionally, snow is blue and mixed precip is pink.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mfb Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2020 at 9:45am
The use of four colors for weather radar display isn't a bug. It's a feature. 

It's designed to meet FAA requirements, as shown in Advisory Circular AC 23.1311-1C  (paragraph 22.4). It is clearly stated there that four colors should be used for display of precipitation.

What's more important, and practical, is that a pilot does not care about the nuances of precipitation levels. He or she just wants to stay away from the bad stuff. 

The NEXRAD radar system doesn't know anything about colors, it just knows about the intensity of the radar return. That's measured in units called "dBz," which is what the radar system reports to any display device. It's up to the device to translate dBz into colors.

A pilot should use caution around radar returns of 30-40 dBz and should stay well away from convective returns of 40 dBz or greater. The 30-40 dBz range is usually shown as yellow, and above 40 is red or magenta.

The four-color mode of Foreflight clearly shows this relationship of color to dBz. Four colors are much easier to interpret, and show the bad areas much more clearly, than 16 colors. I haven't been able to find a similar dBz-to-color table for Avidyne, but I suspect that it's similar to Foreflight. "Stay out of the red" is a simple rule that even I can remember when things get busy. I don't want nuances. I just want to know what to stay away from.

As for weather looking worse than it really is, which way would you rather have it? Not too many pilots have been killed by staying away from weather that wasn't as bad as they thought it was. You can't say the same about pilots flying into weather that wasn't as good as they thought it was.

Mike


Foreflight Weather Radar Display Color Chart





Edited by mfb - 16 Jul 2020 at 9:51am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 310pilot Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2020 at 5:03pm
The AC referenced above does indeed specify four colors but it also gives a large range of precipitation intensities that correspond to a specific color. Other vendors have taken the guidance in this AC and made the level of precipitation more useable to the pilot by adding shades of each of the four colors to most accurately paint the weather intensity. 

Maybe it’s just me but I strongly disagree with the statement:
What's more important, and practical, is that a pilot does not care about the nuances of precipitation levels. He or she just wants to stay away from the bad stuff”

If I’m stuck in an area of weather for whatever reason it would be most helpful to know what the higher/lower intensity areas are and not just see a yellow mass.



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Post Options Post Options   Thanks (0) Thanks(0)   Quote paulr Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2020 at 5:20pm
Notice what Steve said above: "FIS-B weather is displayed according to the requirements of RTCA DO-267A." XM isn't FIS-B. My guess would be that the MX-20 is displaying it using its own color scale, which AFAIK is permitted to do. DO-267A requires the use of the 4-color display for airborne radar data and FIS-B; I don't know what if anything it says about XM WX.

As mfb and Steve posted, the use of 4 colors in the IFD is intentional and was done to follow the FAA's requirements.

FWIW I had the same question back in 2017 and the surrounding discussion was pretty enlightening. You might find this (ancient) thread helpful:

http://forums.avidyne.com/stratus-vs-ifd-skytrax-adsb-weather_topic1292.html




Edited by paulr - 16 Jul 2020 at 5:22pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 310pilot Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2020 at 5:40pm
Thanks Paulr that link was indeed very helpful. To quote that link:

In the event, the Foreflight presentation was much closer to the actual conditions. It was also much closer to the more detailed NEXRAD view I was seeing on my phone. No convection, maybe a 20kt headwind, and some light to moderate rain falling from a higher layer”

This quote illustrates what I am saying. By only using four colors the IFDs weather often does not match the actual weather conditions and would be a lot more accurate and usable if the IFD incorporated shades of the four required colors to most accurately depict the precipitation intensity.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote paulr Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2020 at 5:42pm
While I am not arguing against your point, I don't think I can add anything else useful: the IFD follows the RTCA standard and that is that. They're not gonna change it no matter how much we ask 'em to.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mfb Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jul 2020 at 8:14am
Originally posted by paulr paulr wrote:

The IFD follows the RTCA standard and that is that. They're not gonna change it no matter how much we ask 'em to.

Yup

And please don't forget: ADS-B or XM weather radar is not for tactical thunderstorm penetration, it's for strategic weather avoidance. The weather shown on your screen is at least 10 minutes old and the "nuances" are probably gone by the time you get to them. The objective is to stay well away from the precip areas, not pick your way through them.


Edited by mfb - 17 Jul 2020 at 8:22am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 310pilot Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jul 2020 at 9:08am
The unfortunate reality is that I’m sure you are correct. My request is short sighted anyways because Avidyne has not came up with a suitable replacement for the MLB700. Without a long term plan on keeping XM on the IFD it doesn’t really matter anyways. Unfortunately for me the IFDs weather display limitations mean I will always need another display in the cockpit to provide a more accurate picture of the weather. One of the reasons I purchased the IFD was for it to be the long term replacement for the MX20 (the Mx20 really got the weather display correct) and unfortunately the IFD is not meeting my need in this area.

Edited by 310pilot - 17 Jul 2020 at 12:02pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 310pilot Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jul 2020 at 1:48pm
Here is the scale that Garmin uses. It is from AC 00-24. 
As you can see it uses different shades of colors to best represent the weather. 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote comancheguy Quote  Post ReplyReply Direct Link To This Post Posted: 30 Jul 2020 at 4:35pm
I'd like the see the IFD scroll the radar shots, so that one could see the motion / change over time.  I'll have to keep my old 496 handheld for that. 


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