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Old 04-11-2016, 15:15   #1
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Display Altitude in Dashboard or else

Hello everyone,

As you may understand from the title, I'm not exactly a nautical cruiser. But I found OpenCPN a convenient tool for elementary air navigation.
I'd like to allow OpenCPN to display altitude, e.g. in the bottom tray (alongside position, speed, scale). Do you see any way to easily program that ?
Or to program an element in the Dashboard for that ?
Besides, is it possible to allow the trace to record that information from NMEA ?

Many thanks for you help,

Nicotec
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Old 04-11-2016, 16:31   #2
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Re: Display Altitude in Dashboard or else

I know that there are some real pilots on here, and I'm just a former private pilot, so maybe I should wait for them to comment ... but I won't.

My first reaction is that this is a bad idea, simply because OpenCPN uses nautical charts, which show things of interest to those who stay at sea (or lake) level, but misses a lot of things that are very important to aviators - elevation of various landmarks, for example.

I can understand that it's an easy tool for planning, but am not sure of the value of planning that is done without taking such things into account.
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Old 04-11-2016, 17:28   #3
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Re: Display Altitude in Dashboard or else

Nicotec..
The GPS antenna altitude is present in several GPS NMEA messages, like for example the GGA message.
It can for sure be programmed in either way you suggest but since OpenCPN is a program for us normally at sea level the information is useless for most users. Unless you can't program it for yourself it's unlikely any programmer will take the time for this.
But the way for future requests is to log in and raise a ticket in our Tracker/Flyspray: OpenCPN::OpenCPN00 Feature Request: Tasklist You never know, you may have luck if you try?
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Old 05-11-2016, 03:44   #4
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Re: Display Altitude in Dashboard or else

Greetings and welcome aboard the CF, Nicotec.
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Old 05-11-2016, 16:03   #5
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Re: Display Altitude in Dashboard or else

Nicotec, you could get one of your programming buddies to program such an instrument for Dashboard, then share it, using github. The only time we might use it is going down a river or over a falls, unless it proves useful when taking depth soundings to adjust for tide (doubt it is accurate enough though).
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Old 05-11-2016, 16:41   #6
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Re: Display Altitude in Dashboard or else

Quote:
Originally Posted by rgleason View Post
Nicotec, you could get one of your programming buddies to program such an instrument for Dashboard, then share it, using github. The only time we might use it is going down a river or over a falls, unless it proves useful when taking depth soundings to adjust for tide (doubt it is accurate enough though).
Reminds me of that time on the Niagara River, upstream of the falls, when we were having engine problems
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Old 06-11-2016, 08:25   #7
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Re: Display Altitude in Dashboard or else

I won't express this well, but maybe it will suffice to say any gps I have is always wrong by 16-20 meters per my reality on a good day.. Right now, with a not-great fix my smartphone thinks it is 168 meters above sea level.... a certain amount of research and fiddling is going to be required to make gps altitude useful.
You should turn on your gps and see what error you have now.
The wgs84 model is about +16 to +-20 meters versus a local map that reflects "reality"(NAD83) pretty well....That said, a gps can indicate a comparison between where you started and where you climbed within 10 meters on a good day. ..so I guess any plugin would need a calibration to the datum used in your local map source...here's an example cropped from a comparison of WGS84 with NAD83..
Click image for larger version

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ID:	135184

An air pressure nmea output (a barometer) might be more accurate, but needs calibration
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Old 06-11-2016, 08:50   #8
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Re: Display Altitude in Dashboard or else

The error in height, or Z is roughly twice the error observed for X and Y (lat/lon).
If you have a random error of 10m in X and Y, count with 20m for height/Z.

The other issue Happy already mentioned is the undulation or the Geoid used.
WGS84 applies a rather simple Geoid, there are other models based on the observed gravity deviations to get a closer match with other terrestrial (and calibrated) methods.
Important for surveyors, not so much for boating - don't know how flying fishes navigate though.
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Old 06-11-2016, 10:46   #9
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Re: Display Altitude in Dashboard or else

Quote:
The error in height, or Z is roughly twice the error observed for X and Y (lat/lon).
well there ya go....so, until the hardware improves I am happier being "placed" on a good map that has been created with better tech than I can carry.

Click image for larger version

Name:	topocrop.jpg
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ID:	135193

that said, this is one I made from vector data available free from the government...(OVERmade perhaps because I can't remember offhand what the actual accuracy of the original dem/shp was so it may be interpolation at my end).
still,("blue sky"), if Opencpn were ever to come ashore, maybe a plugin might be possible to "interpolate" from shape data so a map wouldn't be cluttered with all these lines versus "features" ( cliffs,roads,trees,clearings cliffs trails etc)

Other applications already specialise in some of this but I don't doubt the OpenCPN team could do it better if they wanted to!
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