Dead reckoning and radio horizont circles
Heikki Hannikainen
Dead reckoning and radio horizont circles were added to aprs.fi today.
Full story in the blog:
http://blog.aprs.fi/2012/03/dead-reckoning-and-horizont-circles.html
- Hessu
Lynn W Deffenbaugh (Mr)
http://aprs.fi/#!mt=roadmap&z=7&call=a%2FKC0CVU-10&timerange=3600
First question, why does it initially appear at the specified zoom and
immediately zoom in closer hiding what I'm trying to show?
What I'm trying to show is a fixed station transmitting a really high
altitude resulting in the radio horizon circles being shown. Not an
issue to me, but I thought you might like to see it. (Drives me nuts in
APRSISCE/32, in point of fact, and I'm looking at a way to apply terrain
knowledge to use altitude minus ground level to determine when to show
my footprints).
Second question, what's magic about 5 degrees or 2,648 feet? I see your
pair of circles, but having watched many balloon tracks in APRSISCE/32
with an unfiltered RF feed, the to-the-ground horizon accurately tracks
the actual RF reception of the balloon in areas where the terrain is
mostly flat. And where it's not, 2,648 feet doesn't really apply, does it?
Looking for education and trying to decide if an alternate, smaller
footprint would be worth doing in APRSISCE/32 (or maybe a
user-specifiable footprint elevation limit).
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32
Heikki Hannikainen
> http://aprs.fi/#!mt=roadmap&z=7&call=a%2FKC0CVU-10&timerange=3600
>
> First question, why does it initially appear at the specified zoom and
> immediately zoom in closer hiding what I'm trying to show?
That's a genuine bug. The specified zoom should override.
> What I'm trying to show is a fixed station transmitting a really high
> altitude resulting in the radio horizon circles being shown. Not an issue to
> me, but I thought you might like to see it. (Drives me nuts in APRSISCE/32,
> in point of fact, and I'm looking at a way to apply terrain knowledge to use
> altitude minus ground level to determine when to show my footprints).
Yeah. Maybe it should be done based on the symbol only, so that it'd only
ever be done for balloons and airplanes (although I feel that's quite
wrong, too).
Google has an API to fetch elevation information for coordinates, but it's
rate limits might be too restrictive. The Shuttle Radar Topography Mission
data seems to be available, in theory one could import it and do lookups
from that: http://www2.jpl.nasa.gov/srtm/ - but it's quite a project, too.
The data set is probably not very small.
> Second question, what's magic about 5 degrees or 2,648 feet? I see your pair
> of circles, but having watched many balloon tracks in APRSISCE/32 with an
> unfiltered RF feed, the to-the-ground horizon accurately tracks the actual RF
> reception of the balloon in areas where the terrain is mostly flat. And
> where it's not, 2,648 feet doesn't really apply, does it?
There's nothing magic about 2648 feet, that's just the altitude the plane
in the screen shot happened to be flying. I accidentally left a
cut-n-paste artifact in the blog post body :) Removed it now.
5 degrees has been obtained using a Stetson-Harrison research method by
the mostly-UK-based high altitude balloon group. They have a neat balloon
tracker at http://spacenear.us/tracker/ - I think I might try to "learn
from" the altitude bar indicator, too. :) They've empirically found the
5-degree circle to be an useful receive distance estimation when you're
trying to receive the balloon's transmission in a tracking group's car
with some amount of obstructions in their average terrain. They have
plenty of non-flat terrain, too, and they do balloon tracking on 70 cm FSK
RTTY (due to local regulations, and better decoding with low signal).
> Looking for education and trying to decide if an alternate, smaller footprint
> would be worth doing in APRSISCE/32 (or maybe a user-specifiable footprint
> elevation limit).
User-tunable elevation might actually be a nice idea!
- Hessu
Tom Hayward
Ah, that explains why there appear to be so many stations aloft over
Denver today.
1000m is a little low for us mountain folk. I suppose there's no good
way to calculate average terrain height, is there.
Tom KD7LXL
Steve Daniels
house symbol for whatever reason.
You might find http://www.s3research.com/flightdata/ useful, launch and
burst detection for balloons is also sent through Lynn's ANSRVR through my
balloon group you could just look for data from KF7MVY-15 Jerry Gable
Steve Daniels
G6UIM
Torbay Freecycle Moderator
> elevation limit).
- Hessu
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Lynn W Deffenbaugh (Mr)
Height above known terrain is going to be the most reliable, but also
the most difficult to get, unfortunately. Even a user-configurable
lower threshold only works when they're looking in their normal stomping
grounds. Here in Florida, anything over 300 feet is interesting, but if
I zoom over to check out Colorado with that setting, everything will end
up with circles.
Even the "flying" symbols are problematic when you consider some of the
balloons and airplanes that drive along the ground, and the hikers that
go 140mph at 5,000 feet.
Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32
Heikki Hannikainen
> Even the "flying" symbols are problematic when you consider some of the
> balloons and airplanes that drive along the ground, and the hikers that go
> 140mph at 5,000 feet.
>
> Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32
>
> On 3/28/2012 4:51 PM, Steve Daniels wrote:
>> Please don't do it on the symbol as the recent transatlantic balloon had a
>> house symbol for whatever reason.
My normal response to weird display in case of incorrectly configured or
illegal transmissions has been to display it, so that it's visible an can
be fixed. So, if some transatlantic balloon has been configured as a
house, it probably should be treated as one.
(With the exception of network-design-induced issues such as the duplicate
and old packets, which the end-user has no means to fix.)
- Hessu
Heikki Hannikainen
Hi,
I did it based on the symbol. Radio horizon circles are now only drawn for
airplanes and balloons.
Also, the !x! no-archive flag now works both in the beginning and in the
end of the comment string. An unrelated little fix.
- Hessu
OK1ALX
please add Glider symbol to the list also ;)
So far i found these symbols which should be considered as flying objcets:
Small Aircraft - /'
Baloon - /O
Helicopter - /X
Glider - /g
Large Aircraft - /^
Rocket - \O (not sure on this)
Satellite - \S (not sure on this)
| |
Aircraft (with overlay) - \^ Libor, OK1ALX |
Dne úterý, 3. dubna 2012 22:37:43 UTC+2 Heikki Hannikainen napsal(a):
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>
- Hessu