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  #221  
Old March 20th 17, 12:33 PM posted to rec.bicycles.tech
John B.[_3_]
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On Sun, 19 Mar 2017 23:59:36 -0700, Jeff Liebermann
wrote:

On Mon, 20 Mar 2017 12:25:07 +0700, John B.
wrote:

The marine GPS' that I've used were all WGS84.


Yep. That's the usual default setting.

Generally speaking those who sail outside the U.S., are using British
Admiralty charts, or copies there of. I used to buy Thai charts from
the Thai Navy and they were based on Admiralty charts. I don't
remember but I think that they were not WGS84.


NOAA nautical maps use NAD83 (which is very close to WGS84).
USGS uses NAD27 but is slowly moving to NAD83.
Google Earth uses WGS84.
Geocaching uses WGS84.

Here's what the military thinks of "civilian" charts:
http://msi.nga.mil/MSISiteContent/StaticFiles/Files/NautChrts_GPS_index.htm
"Isolated datums, such as those used to position many islands
in the Pacific Ocean, can be in error by a half mile or more
(see figure). The datum shift to WGS 84 can be quite large,
depending on the area of the world and the local datum in use."

See the chart of Farallon De Pajaros Island, which requires a 1/2
nautical mile shift for the map to agree with GPS.
http://msi.nga.mil/MSISiteContent/StaticFiles/Files/island.jpg

But datum aside, I had a copy of a chart of an island in the S.
Pacific and the notes stated, it was based on surveys made by the HMS
something or another, in 1790-something. I always thought that if I
ever got onto the S. Pacific that I would approach those islands in
the daylight with great care :-)


Possibly Captain James Cook, who went through the south pacific
between 1768 to 1771.
https://en.wikipedia.org/wiki/European_and_American_voyages_of_scientific_explor ation

:-) No, it was later than that :-)

I have a nice Tamaya sextant, out of date HO 229/249 tables, and some
charts. It's not very practical these days, but it does help one
understand how such things work.


Way back when, I went to considerable effort to learn proper
navigation. Sextant, HO tables and lessons from the lead navigator in
a B-52 squadron. What sort of took the shine off the effort was when I
did the usual three shot position and got a "cocked hat"that was about
a mile and a half on each side. When I told the Major about it he
commented that I was doing real good. I replied that I didn't think
that a triangle that was a mile and a half on each side wasn't very
accurate he assured me that it was "pretty good for celestial
navigation.... which is why we don't use that for the B-52's" :-)
--
Cheers,

John B.

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  #222  
Old March 20th 17, 04:48 PM posted to rec.bicycles.tech
Jeff Liebermann
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On Mon, 20 Mar 2017 18:33:51 +0700, John B.
wrote:
Way back when, I went to considerable effort to learn proper
navigation. Sextant, HO tables and lessons from the lead navigator in
a B-52 squadron. What sort of took the shine off the effort was when I
did the usual three shot position and got a "cocked hat"that was about
a mile and a half on each side. When I told the Major about it he
commented that I was doing real good. I replied that I didn't think
that a triangle that was a mile and a half on each side wasn't very
accurate he assured me that it was "pretty good for celestial
navigation.... which is why we don't use that for the B-52's" :-)


Accurate navigation with an aviation sextant is far more difficult
than marine navigation. If you were doing celestial or lunar
navigation on the ground, using an averaging bubble sextant artificial
horizon, I would say 1.5 miles was doing very good. If you were doing
it while flying, amazingly good.

I'm told that marine navigation is easier. Many years ago, I dragged
a gaggle of middle skool slackers to the end of the local breakwater,
which features a miniature lighthouse that's almost exactly at -122.0
deg longitude.
http://www.lighthousefriends.com/light.asp?ID=836
It was a clear day and the horizon was clearly defined. It was almost
noon, so I started by showing them how to take a noon sight. I was a
bit more than a nautical mile off. Oops. I brought along a WWV
receiver for doing latitude, but the signal was too weak to be usable.
Using someone's inaccurate wrist watch, I located our position about 5
nautical miles away. Lunch and a side trip to the local amusement
park was sufficient to salvage my reputation.

Some additional navigation horror stories using Omega, Loran (lane
skipping), Navsat, inertial navigation, and direction finding using
radio towers, but this is getting too far of topic (whatever that
might be). The tower story is interesting. The FCC database records
the "location" of each radio station licensee. One might assume that
this means the location of the transmitting tower. Instead, it's
usually the location of the studios or offices. Someone published a
navigation map using the FCC locations instead of the tower locations
resulting in RDF (radio direction finding) receiving a bad reputation
for poor accuracy when used for navigation.



--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #223  
Old March 20th 17, 06:51 PM posted to rec.bicycles.tech
Joerg[_2_]
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On 2017-03-19 15:01, Jeff Liebermann wrote:
On Sun, 19 Mar 2017 10:29:45 -0700, Jeff Liebermann
wrote:

Somewhere in my mess is a Windoze program that takes this data and
provide both graphical and tabular accuracy statistics. I used to use
it when we had to deal with selective availability. It's kinda neat.
You park yourself in a highly reflective location (bottom of a rock
canyon) and record about 30 mins of position data. Position
excursions on the display are obvious. I use it for averaging
readings over a long period in order to obtain better accuracy.


Foundit.

Visual GPS:
http://www.visualgps.net/#visualgps-content
It's free and old but works nicely.

Visual GPS XP works somewhat better, but costs $10:
http://www.visualgps.net/#visualgpsxp-content

New, improved, and free is Visual GPS View:
http://www.visualgps.net/#visualgpsview-content

All these will graphically show any radical excursions in position.

I have several battery powered, BlueGoof GPS receivers. They're quite
convenient for testing with VisualGPS. However, I prefer to use an
RS232 data logger, which works on any GPS. After collecting data for
maybe 30 minutes, I dump the output into the Visual GPS program and
inspect the resulting mess.


Nice, but its kind of tough to schlepp all this along on an MTB through
dirt and stuff.

--
Regards, Joerg

http://www.analogconsultants.com/
  #224  
Old March 20th 17, 07:01 PM posted to rec.bicycles.tech
Doug Landau
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Posts: 1,338
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On Monday, March 20, 2017 at 8:48:05 AM UTC-7, Jeff Liebermann wrote:
On Mon, 20 Mar 2017 18:33:51 +0700, John B.
wrote:
Way back when, I went to considerable effort to learn proper
navigation. Sextant, HO tables and lessons from the lead navigator in
a B-52 squadron. What sort of took the shine off the effort was when I
did the usual three shot position and got a "cocked hat"that was about
a mile and a half on each side. When I told the Major about it he
commented that I was doing real good. I replied that I didn't think
that a triangle that was a mile and a half on each side wasn't very
accurate he assured me that it was "pretty good for celestial
navigation.... which is why we don't use that for the B-52's" :-)


Accurate navigation with an aviation sextant is far more difficult
than marine navigation. If you were doing celestial or lunar
navigation on the ground, using an averaging bubble sextant artificial
horizon, I would say 1.5 miles was doing very good. If you were doing
it while flying, amazingly good.

snip


Lookit that, 50 years later, you're finally exonerated.


  #225  
Old March 20th 17, 07:04 PM posted to rec.bicycles.tech
Joerg[_2_]
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Posts: 4,624
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On 2017-03-19 10:29, Jeff Liebermann wrote:
On Sun, 19 Mar 2017 08:34:51 -0700, Joerg
wrote:
Miles is bad. That means a position indication is useless for any
serious trail riding.


Not exactly. It depends on what you're doing. If you try to plot
your ride, you might get some screwed up data points mixed in with the
data. For example, my last hike into the bottom of a local canyon
yielded a maximum altitude of 3,000 feet higher than the ground.



That's a problem. One of the challenges with MTB riding is that a
satellite map might show a trail but then two things can happen:

After many, many miles you arrive at a fence with a sign stating in no
uncertain terms that this is not to be crossed.

Or, after a few miles you find that the trail leads over the steepest
hill this side of the Klondike and you are almost out of time as it is.

Regarding altitude at my current position I can take along my
parachuting altimeter. It is very rugged and accurate.

... There
was only one or two bad data points, but it was enough to screw up all
the statistics. Same with maximum speeds traveled, where the distance
covered between a real position indication and a bogus point or two is
high enough for me to claim breaking the sound barrier.

Mapping software authors know about all this and do their best to
compensate. The most common and best method is to do a sanity check
on all positions. If the GPS suddenly claims you've instantly moved
many miles, that point gets dropped. You probably won't see garbage
data on your smartphone or mapping GPS because of this feature. You
will see garbage if you use raw NMEA-183 data in some application. If
you want to see if you have a potential problem, just connect a data
logger to the GPS and collect some $GPGLL sentences. Write a program
that looks for large changes in adjacent sentences. The glitches, if
present, should be drastic and obvious.

Somewhere in my mess is a Windoze program that takes this data and
provide both graphical and tabular accuracy statistics. I used to use
it when we had to deal with selective availability. It's kinda neat.
You park yourself in a highly reflective location (bottom of a rock
canyon) and record about 30 mins of position data. Position
excursions on the display are obvious. I use it for averaging
readings over a long period in order to obtain better accuracy.

Are at least the maps and the satellite view as
good as on a PC? As long as it buffers enough before going off-grid that
would help because I can fix my position pretty well via the use of
landmarks. Good old triangulation.


I'm not sure. Everything depends on the antenna sensitivity and
bandwidth.



Not if a satellite map can be downloaded before the ride and has at
least some crude altitude info. Then I could ride sans GPS for long
stretches using only landmarks for orientation.


... There's a huge difference in performance between an
antenna that uses a choke ring to reduce ground reflections as on
survey receivers:
https://en.wikipedia.org/wiki/Choke_ring_antenna
and a smartphone that uses a tiny ceramic patch antenna. These
articles cover the problem quite nicely:
https://www.u-blox.com/sites/default/files/products/documents/GPS-Antenna_AppNote_%28GPS-X-08014%29.pdf?utm_source=en%2Fimages%2Fdownloads%2F Product_Docs%2FGPS_Antennas_ApplicationNote%28GPS-X-08014%29.pdf
http://www.taoglas.com/wp-content/uploads/2015/07/Internal-GPS-Active-Patch-AntennaAPN-13-8-002.B.pdf
Hmmm... probably more than you want to know. Suffice to say that the
smaller the antenna, the narrower the usable bandwidth. This is
important because small antennas work very badly with WAAS and barely
can handle the L1/L2 bands. Gain also suffers. From the Taoglas
article:
Typical peak gain for GPS patch antennas on standardized
ground planes are as follows:
25mm Patch 5 dBi
18mm Patch 2 dBi
15mm Patch 1 dBi
12mm Patch 0.5 dBi
10mm Patch -2 dBi
By comparison to what's found in a smartphone, these patch antennas
are HUGE. I can't seem to find the smartphone GPS antenna vendor, but
as I vaguely recall, the typical gain was about -8dBi with a rather
narrow view of the sky.

Anyway, back to your question... If you look at the antenna, and
assume that the receivers are all rather similar, your performance
will be almost totally dependent on the GPS antenna.


It would be ok to hack it and have an external antenna but I assume that
isn't in the cards for a regular cell phone. Some allow you to plug in
an antenna for the cell bands (a friend needs that to get coverage at
all at their home) but not for GPS.


With me that's a problem because my favorite routes are off-road. I try
to avoid raods whenever possible for many reasons. Like the one
yesterday where a driver came very close and leaned on the horn in an
attempt to push me from the lane to the side. No danger because he had
slowed down to my pace but such low-lifes with a drivers license are
annoying. And dangerous, especially when they are soused or nowadays
high on whatever.


Well, you could weaponize your bicycle to act as a deterrent.
https://www.google.com/search?q=bicycle+gun&tbm=isch


Sometimes I wonder if a concealed carry would make sense on a bike. At
least for cases where some low-life flies into a full road rage and
tries to attack. Or a montain lion wants to pounce :-)


I wore out the BB on my road bike. Again :-(
But it was 40 miles of fun (except for the road part)


Sigh. At least you wore it out and didn't break it. Out of
curiosity, what wore out? Bearings? Raceway? Seals? Mechanical
doping motor?


It suddenly developed a lot of play. Not so much side-to-side but
up-down. That is usually a sign that it's close to EOL. The challenge
will be to find a new square-taper version with the correct geometry.
Else I'd also have to buy new cranks and chain rings.

--
Regards, Joerg

http://www.analogconsultants.com/
  #226  
Old March 20th 17, 07:35 PM posted to rec.bicycles.tech
Sir Ridesalot
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On Monday, March 20, 2017 at 2:04:15 PM UTC-4, Joerg wrote:
Snipped

Sometimes I wonder if a concealed carry would make sense on a bike. At
least for cases where some low-life flies into a full road rage and
tries to attack. Or a montain lion wants to pounce :-)


I wore out the BB on my road bike. Again :-(
But it was 40 miles of fun (except for the road part)



Hah, a mountain lion pounces from above and behind and would be on you before you even knew it was near you. ;)

What you need is a cage completely around your bicycle. MAybe add another wheel or two for better stability and then add a motor to help move it along. :)

Are you saying that you wore out a bottom bracket in only 40 miles of use? That's what it sounds like from what you posted.

Cheers
  #227  
Old March 20th 17, 07:44 PM posted to rec.bicycles.tech
Jeff Liebermann
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On Mon, 20 Mar 2017 10:51:29 -0700, Joerg
wrote:

Nice, but its kind of tough to schlepp all this along on an MTB through
dirt and stuff.


You don't drag the computah with you. You take along a GPS and a data
logger or GPS tracker. The data logger collects the NMEA-0183 data
from the GPS. You play it back to the VisualGPS program(s) when you
get home (or in your vehicle if you bring along a laptop).
https://www.google.com/search?q=gps+data+logger&tbm=isch
The big problem is battery life. The pocket size data loggers are
designed to sample the GPS data, while you probably want continuous
data collection. You might need an external battery.


--
Jeff Liebermann
150 Felker St #D
http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
  #228  
Old March 20th 17, 07:52 PM posted to rec.bicycles.tech
SMS
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Posts: 7,997
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On 3/20/2017 11:35 AM, Sir Ridesalot wrote:
On Monday, March 20, 2017 at 2:04:15 PM UTC-4, Joerg wrote:
Snipped

Sometimes I wonder if a concealed carry would make sense on a bike. At
least for cases where some low-life flies into a full road rage and
tries to attack. Or a montain lion wants to pounce :-)


I wore out the BB on my road bike. Again :-(
But it was 40 miles of fun (except for the road part)


Hah, a mountain lion pounces from above and behind and would be on you before you even knew it was near you. ;)


Yes, that's the big problem with mountain lions. You can't even use bear
spray because it'll be too late to spray. There are some predation
control devices with some efficacy but not 100%.
http://www.mountainlion.org/imagesportals/portalprotect/APHIS%20Electronic%20Guard.pdf.
Battery powered.


  #229  
Old March 20th 17, 08:03 PM posted to rec.bicycles.tech
Joerg[_2_]
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On 2017-03-20 11:44, Jeff Liebermann wrote:
On Mon, 20 Mar 2017 10:51:29 -0700, Joerg
wrote:

Nice, but its kind of tough to schlepp all this along on an MTB through
dirt and stuff.


You don't drag the computah with you. You take along a GPS and a data
logger or GPS tracker.



Then back at home I can tell my wife "See, honey, this is the reason why
I became lost and had to pitch a tent out in the boonies".


The data logger collects the NMEA-0183 data
from the GPS. You play it back to the VisualGPS program(s) when you
get home (or in your vehicle if you bring along a laptop).



My MTB _is_ my vehicle, from garage all the way back to garage :-)


https://www.google.com/search?q=gps+data+logger&tbm=isch
The big problem is battery life. The pocket size data loggers are
designed to sample the GPS data, while you probably want continuous
data collection. You might need an external battery.


I just want a map to see where I am and where I could go, while on the
ride. Preferably in a way that it won't steer me into an off-limits
quarry, a rancher with a shotgun, or something like that.

--
Regards, Joerg

http://www.analogconsultants.com/
  #230  
Old March 20th 17, 09:31 PM posted to rec.bicycles.tech
Joerg[_2_]
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Posts: 4,624
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On 2017-03-20 11:35, Sir Ridesalot wrote:
On Monday, March 20, 2017 at 2:04:15 PM UTC-4, Joerg wrote: Snipped

Sometimes I wonder if a concealed carry would make sense on a bike.
At least for cases where some low-life flies into a full road rage
and tries to attack. Or a montain lion wants to pounce :-)


I wore out the BB on my road bike. Again :-( But it was 40
miles of fun (except for the road part)


Hah, a mountain lion pounces from above and behind and would be on
you before you even knew it was near you. ;)

What you need is a cage completely around your bicycle. MAybe add
another wheel or two for better stability and then add a motor to
help move it along. :)

Are you saying that you wore out a bottom bracket in only 40 miles of
use? That's what it sounds like from what you posted.


No, it just happened on that ride. RRRT .. RRRT .. now what the heck is
that? Looked down, chain rings sloshes left to right. This one lasted
probably around 10k miles. Not great but still better than 3-4k in my
student days. I guess that (plus spokes, rear tires, cassettes and
chains) is the price to pay for living in the hills. Yesterday I popped
a spoke. Again.

The bottom bracket has to limp along for a while until I have time to
fix my MTB where I wore out stuff at its rear end. Can't be without a
(at least somewhat) working bike.

--
Regards, Joerg

http://www.analogconsultants.com/
 




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