[DeTomaso] Speedhut versus Autometer gauges help

Sun Jan 20 16:10:20 EST 2013

Hi Gary,

This is correct. It's now possible achieve 2--4 inch pass-by-pass accuracy
through a field (repeatable). And all using commercially available GPS
receivers. However, the cost is in the engineering that goes into the
auto-steer control system, touch panel display, and the software to process
GPS signals from multiple antennas to also provide orientation (i.e. roll,
pitch, and yaw). The cost of the GPS unit is not what drives up the cost. I
used to consulted for Norvariant from 1996 until 2004 (formally
IntegriNautics) and went to school with the founders while at Stanford.

  http://www.gpsfarm.com/Products/OnTrac2/tabid/112/Default.aspx
  http://www.gpsfarm.com/Technology/PrecisionPosition/tabid/169/Default.aspx

http://www.gpsfarm.com/Technology/AdvancedControlSystem/tabid/170/Default.aspx
  http://www.gpsfarm.com/About/tabid/60/Default.aspx

The current company is focused entirely on GPS farming and has removed
almost all reference to the original company named IntegriNautics from
their website. IntegriNautics patented the idea of using multiple antennas
and calculating the phase angle of the two RF carrier frequencies (L1 and
L2) for GPS as the signal passes over each antenna. With this technology
they were able to achieve real-time centimeter-level accuracy plus
orientation to a fraction of a degree by determining the position of
multiple antennas. Here's the key patent describing this.

http://www.sumobrain.com/patents/wipo/Multiple-antenna-multi-frequency-measurement/WO2003044556.html

It is called Carrier-Phase Differential GPS. This was used in aircraft in
the 1990s for auto-landing tests, including over 100 hands-free landings of
a United 737. Note, this was before the government stopped degrading the
accuracy of the civilian GPS signal. Searching the Internet about all I can
find about this is on the website for the Gravity Probe-B NASA mission to
test Einstein's General Theory of Relativity.

  http://einstein.stanford.edu/highlights/hl_033106.html

Search for Clark Cohen in this page and you can read the early history of
the development of this technology. It was used on the the Gravity Probe
spacecraft mission in a polar orbit 400 miles above the earth. Clark's
Ph.D. thesis is
here<http://waas.stanford.edu/~wwu/papers/gps/PDF/Thesis/ClarkCohenThesis92.pdf>.
As an aside, the science gyros on-board Gravity Probe-B are the roundest
man-made objects ever and are a million times more accurate than the best
we have, which are those on the Hubble space telescope or possibly those on
our nuclear powered subs. I consulted for Gravity Probe-B for 10 years and
it was one of the most amazing projects I've worked on.

As others have said there is no speed limitation on receivers using the
civilian channel of the GPS signal. Now days the accuracy of the civilian
and military signals are the same. However the military signal is broadcast
on two carrier frequencies, which can be used to reduce the errors
introduced by the ionosphere.

  http://www.gps.gov/systems/gps/performance/accuracy/

It's used for aircraft and spacecraft all the time. The primary things that
affect the accuracy of a GPS based speedometer are the view of the sky for
satellites, multi-path signals from bouncing off things like buildings in a
city or canyon walls, location of the antenna, the number of channels in
the GPS receiver, and the sample rate of the GPS position by the
speedometer. Assuming good visibility of the sky and minimal multi-path,
the sample rate of the signal will have the largest impact on accuracy and
lag in the display. If the speedometer is only sampling every few seconds
the speed measurement will lag quite a bit. There will be some low-pass
filtering of the difference in the position measurements in order to keep
the reading from jumping back and forth due to the errors in the GPS
position measurement, which can be as much as +-10 feet without some type
of differential reference signal. So I would expect a good speedometer to
be sampling at least 1 times per second, which is the rate that nearly all
smartphones can do. Faster sampling is better, so 5 to 10 times per second
would be better. I've read some rumors that some of the new smartphones
coming out will support 5 Hz GPS sampling.

However, with additional sensors this could be improved quite a bit. All
modern smartphones have accelerometers built into them. So if you are
driving down a smooth flat road at a constant speed the accelerometers will
show no change even though the GPS position may say that you jumped 1 foot
to the right between the last measurement and this one. The accelerometer
data can smooth all of this out. And if you are turning or accelerating the
accelerometers will also tell you that. Not only that, the accelerometer
data can carry you through a brief loss of GPS signal. So a great GPS
speedometer would have a fast sample rate of the GPS signal as well as
accelerometers.

Cheers,

Denny
----

On Fri, Jan 18, 2013 at 3:09 PM, Gray Gregory <rgg at gregorycook.com> wrote:

> The GPS units used to run the auto steering in big farm tractors are very
> accurate (to about 4" or less) but they do cost considerably more than
> automotive units.
>
> Gray
>
> -----Original Message-----
> From: detomaso-bounces at poca.com [mailto:detomaso-bounces at poca.com] On
> Behalf Of gow2 at rc-tech.net
> Sent: Friday, January 18, 2013 4:23 PM
> To: Boyd Casey
> Cc: Charles McCall; detomaso at poca.com; michael at michaelshortt.com; Ed
> Mendez
> Subject: Re: [DeTomaso] Speedhut versus Autometer gauges help
>
> There are a couple different reasons for Aircraft GPS being more
> expensive. One is they typically require more satellites to confirm
> navigation. They also notify you of accepted navigation levels because of
> available satellites and due to messages satellite give out about their
> integrity.
>
> Anything not aviation just takes the signal they get and say here it is.
>
> Also, Aviation is certified to a high degree of scrutiny and lower
> production then other GPS marketed for the general use. It means a high
> price but not necessarily a better unit.
>
> GPS tracking is not that hard. Cheap devices doing computations will be no
> less accurate then expensive devices. They all read the same signal.
>
> As far as the sat moving, it is not about the movement of the sat
> refference. That is minor or slow to the point it has no effect on the
> accuracy of speed; only that the map is off.
>
>
>
>
> > As  I said , I knew  a certain degree a certain degree of locational
> > information was intentionally erronious. The speed information may
> > have been urban legend or perhaps the unit in question was not  new
> > enough or the GPS  being used was  a portable aviation unit. They make
> > portable pilot  GPS thigh mounted  units that need to be able to meet
> > the speed and altitude limits of aircraft the are intended to be used
> > in. I believe the articcle I read refered to Automotive GPS units. The
> > air craftgps devices are considerabelly more expensive. I picked up my
> > last Tom Tom for $99 bucks. The gist of this article was "build a
> > cruise  missle for  $1000 (or something along those lines.  I first
> > read this article years ago and the last thing I remember about the
> > whole subject the Government ( New Zealand or Austrailia) put the
> > Kalashnikov on the whole thing. I believe they approached the author
> > and warned him about " actions that were contrary to the "national
> > security interests" and or the risk of being kidnapped by Al Queda or
> > Iran etc. So that was that. Just now I searched and found this link.
> >
> > http://www.aardvark.co.nz/pjet/cruise.shtml
> >
> > On Friday, January 18, 2013, Ed Mendez wrote:
> >
> >> I appreciate the feedback on these gauges. The seam better than
> >> Autometer then. So thanks.
> >>
> >> Can someone tell me the size of the factory tach and speed? 5" 4", etc.
> >>
> >> Ed
> >>
> >>
> >> On 18/01/2013, at 12:30 PM, Roland Jaeckel <pantera874 at t-online.de>
> >> wrote:
> >>
> >> > Brake down and speed up and see then, how fast it follows. We tried
> >> > it
> >> on track and it couldn't show the speed at any time right.
> >> > In town, the same situation.
> >> >
> >> > --------------------------------------------------
> >> > From: "Charles McCall" <charlesmccall at gmail.com>
> >> > Sent: Friday, January 18, 2013 8:23 PM
> >> > To: "'Boyd Casey'" <boyd411 at gmail.com>; "'Roland Jaeckel'" <
> >> pantera874 at t-online.de>
> >> > Cc: <michael at michaelshortt.com>; "'Ed Mendez'" <edducati at mac.com>;
> >> > <
> >> detomaso at poca.com>
> >> > Subject: RE: [DeTomaso] Speedhut versus Autometer gauges help
> >> >
> >> >> I turned an early-generation GPS receiver on once on a commercial
> >> airplane
> >> >> flight and it read perfectly well at 600mph so I think that the
> >> maximum
> >> >> speed thing is urban legend.
> >> >>
> >> >> The rest is true - a certain amount of error is built in for
> >> >> security reasons. But I think that is more related to exact
> >> >> location than your
> >> speed.
> >> >>
> >> >>
> >> >> On an open highway with no tall buildings, I get a fairly stable
> >> >> gps
> >> speed
> >> >> on my TomTom and believe it to be more accurate than the stock
> >> >> speedo
> >> >>
> >> >> Charles McCall
> >> >> Raising Pantera Awareness Across Europe
> >> >> 1985 DeTomaso Pantera #9375
> >> >> http://www.poca.com/index.php/gallery/?g2_itemId=2323
> >> >>
> >> >>
> >> >> -----Original Message-----
> >> >> From: detomaso-bounces at poca.com [mailto:detomaso-bounces at poca.com]
> >> >> On
> >> Behalf
> >> >> Of Boyd Casey
> >> >> Sent: viernes, 18 de enero de 2013 20:16
> >> >> To: Roland Jaeckel
> >> >> Cc: michael at michaelshortt.com; Ed Mendez; detomaso at poca.com
> >> >> Subject: Re: [DeTomaso] Speedhut versus Autometer gauges help
> >> >>
> >> >> GPS units have the ability to be incredibly accurate, that's down
> >> >> to millimeters and micro seconds. The problem is this these levels
> >> >> of
> >> accuracy
> >> >> are limited to miltary GPS units. Civilian GPS units are forced by
> >> legal
> >> >> statute to build in varying degrees of error. The governments that
> >> enforce
> >> >> theses regulations are trying to prevent GPS units from being used
> >> >> by terrorist groups .
> >> >> I don't know the particulars but I was told that GPS units
> >> >> designed
> >> for
> >> >> automotive or marine use are also set up so they can't be used in
> >> anything
> >> >> traveling over a particular speed ( like 200 mph). This is
> >> >> supposed
> >> to
> >> >> prevent their use in a home made cruise missel . A few year ago a
> >> >> guy
> >> in
> >> >> New Zeland was offering plans on popular mechanics  to build a
> >> >> cruise missel power erred by a ram jet that was supposed to be
> >> >> able to be constructed with all "off the shelf components,GPS,
> computer, etc"
> >> With
> >> a
> >> >> substantial range and a high speed ( like 500 mph).
> >> >>
> >> >> So you can blame all the errors in GPS  on the government and the
> >> >> terrorists. On a brighter note I had heard that the government
> >> >> had recently lowered  the required degree of error built in on GPS
> units.
> >> >>
> >> >> Boyd
> >> >>
> >> >>
> >> >> On Friday, January 18, 2013, Roland Jaeckel wrote:
> >> >>
> >> >>> In town, they are zero accurate. If they don't have contact to
> >> >>> all satelites, they can't notice, that youre driving thrue a turn.
> >> >>> Whatch for it in town and anywhere while changing speed quickly.
> >> They
> >> >> can't
> >> >>> follow as quick as a convetionel speedo can. They work for a
> >> >>> boat,
> >> but
> >> >> that
> >> >>> is way slower in changing speeds.
> >> >
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