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Old 23-03-2015, 12:04   #46
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Re: Speed Through GPS Versus Old Fashioned Paddle Log

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Originally Posted by Rustic Charm View Post
wow, I have just a boring one, where can I get one that does all that.
Any of the Samsung series Android phones.
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Old 23-03-2015, 12:06   #47
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Re: Speed Through GPS Versus Old Fashioned Paddle Log

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Any of the Samsung series Android phones.
My Samsung doesnt do blood tests.
You fibbed!
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Old 23-03-2015, 12:21   #48
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Re: Speed Through GPS Versus Old Fashioned Paddle Log

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My Samsung doesnt do blood tests.
You fibbed!
You gotta buy the $34 dongle that plugs into the headphone jack. Probably one of the most amazing little inventions I've seen in a while. Wait till they come out with the $50 replacement for the gas chromatograph that can compress your results and email them to an onshore lab for further analysis.

http://9to5mac.com/2015/02/23/iphone-hiv-test/

They're claiming the cassette that takes the sample will eventually be selling for about $4 ea.
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Old 23-03-2015, 13:19   #49
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Re: Speed Through GPS Versus Old Fashioned Paddle Log

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Originally Posted by socaldmax View Post
You gotta buy the $34 dongle that plugs into the headphone jack. Probably one of the most amazing little inventions I've seen in a while. Wait till they come out with the $50 replacement for the gas chromatograph that can compress your results and email them to an onshore lab for further analysis.

$34 iPhone dongle allows 15-minute HIV test with similar accuracy to ‘gold standard’ lab test | 9to5Mac

They're claiming the cassette that takes the sample will eventually be selling for about $4 ea.
Thats not Android....... jes sayin'
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Old 23-03-2015, 13:22   #50
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Re: Speed Through GPS Versus Old Fashioned Paddle Log

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Thats not Android....... jes sayin'
But it does plug into my Android phone. I didn't say the dongle was made by Android, I listed some of the things my Android phone can do.
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Old 23-03-2015, 13:23   #51
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Re: How Does GPS Work?

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Some were confused as to how GPS can produce velocity data without waiting for 2 or more position updates so it can compute speed by distance divided by time. The answer is that velocity is inherent in the algorithm because it uses Doppler shift. If the algorithm has Doppler shift data then velocity comes from that for free. So the receiver does not wait for two or more position fixes. Velocity can be produced very quickly and in real time as far as humans are concerned. Some specialized receivers only produce velocity and don't bother with the position computation to save cost and/or power.
Dan, you are right that user velocity is not based on differencing successive position measurements (the spreadsheet approach to real-time sw ).

User position is initiated by first correlating receiver's locally generated PN sequences (by satellite PRN #) with the received from the satellites (objective is code lock), using a delay lock loop (DLL). The local code is slid (1023 bits) across the received code until a correlation appears (de-spread). This is done per satellite. These random spread spectrum codes are out of the GOLD CODE family, and have good cross-correlation isolation with each other. Once performed, the 50 bit/second nav messages can be demodulated from each, containing sat ID, constellation rough ephemeris, and per satellite precise ephemeris, along with Health Bits, etc. Once 4 satellites have been located this way, the four spheres surrounding these 4 satellites are found to intersect if a specific time is assumed for the user receiver (50 bit message sends GPS time of transmission date for each sat), and where these intersect is the location of the user. End of 4 satellite code lock summary.

Now we have user position and time, but we need to steer the receiver tracking loops (PLL) for the carrier signals (12 channel receiver would have each have a DLL and PLL) until the received signal carrier is locked on in the PLL for each channel. This action, which assists in keeping a solid code lock in degraded conditions, is called carrier lock, and afterwards we will have C/No data available for each channel, in dB/Hz, which is the units for signal strength on most displays. Which way to steer the synthesizer for each channel's PLL, which rest at close to the nominal L1 frequency, comes from knowing user location, earth rotation, and satellite rise (Doppler + ) and set (Doppler -) events, otherwise carrier lock would take a long time to go through all the search space. The satellites are ~ 10 miles away, and the signal power EIRP is 26 watts. Once PLLs are locked to their respective incoming carriers, the PLL tracking loop bandwidths are set to be sufficient for keeping lock for marine users (low dynamics). Now the Doppler effect is readily observed, either by noting the difference between the PLL frequency being used for each satellite versus the nominal L1 frequency, adjusted for Relativity, as a new beat frequency observable, which can be equated with a user velocity directly, or by an integrate and dump approach, which will on small intervals count up the # of carrier cycles obtained, and report on a sub second basis how many wavelengths from X satellite was received. This is then normalized to remove earth and satellite motion effects, leaving user motion towards and away from each satellite. These motions, through an Observation Matrix, relate these signal dynamics to user X-Y-Z rates on the earth.

These data are then feed into the user Nav filter (like an Extended Kalman Filter) to obtain user velocity.
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Old 23-03-2015, 13:25   #52
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Re: How Does GPS Work?

Very good.
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Old 23-03-2015, 13:37   #53
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Re: How Does GPS Work?

After 40 years in the offshore survey business, I never thought I would see people who call themselves sailors arguing over how GPS works. That's like saying there are different opinions on how an internal combustion engine works. It's not subject to opinion.

But then I remember how many times over the years I've found otherwise knowledgeable people who truly believed that they were getting heading info from GPS. Former owner of our boat was 20 year USCG ret. and he didn't understand it.
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Old 23-03-2015, 13:42   #54
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Re: How Does GPS Work?

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After 40 years in the offshore survey business, I never thought I would see people who call themselves sailors arguing over how GPS works. That's like saying there are different opinions on how an internal combustion engine works. It's not subject to opinion.

But then I remember how many times over the years I've found otherwise knowledgeable people who truly believed that they were getting heading info from GPS .
Once GPS has computed horizontal velocity, it has a direction and speed. The horizontal direction can be referenced to true North or magnetic North. So, what is your reasoning that GPS can't be used to get heading? When sitting still, GPS can't be used to derive a heading. But when moving....
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Old 23-03-2015, 14:01   #55
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Re: How Does GPS Work?

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After 40 years in the offshore survey business, I never thought I would see people who call themselves sailors arguing over how GPS works. That's like saying there are different opinions on how an internal combustion engine works. It's not subject to opinion.


GPS is very complex and takes high expertise from many different disciplines to bring it all together. I can see why there are a lot of misunderstandings in this area.



I can recommend who you should be listening to....TransmitterDan and Erickson38...they know what they are talking about. We should all become students when they are talking.
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Old 23-03-2015, 16:40   #56
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Re: How Does GPS Work?

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Once GPS has computed horizontal velocity, it has a direction and speed. The horizontal direction can be referenced to true North or magnetic North. So, what is your reasoning that GPS can't be used to get heading? When sitting still, GPS can't be used to derive a heading. But when moving....
Because heading has nothing to do with the direction the vessel is moving, it is the diection the ship's bow is pointing.

So the vessel may be moving say N but the bow is pointing say NE.

Of course there are more complex GPS compass solutions but the previous post was referring to the straightforward GPS units most of us use on a recreational boat.
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Old 23-03-2015, 16:57   #57
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Re: How Does GPS Work?

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Because heading has nothing to do with the direction the vessel is moving, it is the diection the ship's bow is pointing.

So the vessel may be moving say N but the bow is pointing say NE.

Of course there are more complex GPS compass solutions but the previous post was referring to the straightforward GPS units most of us use on a recreational boat.
This doesn't sound correct to me. I would think your heading 'is' the direction you want to move the vessel in regardless of where the bow is pointing. I might for example, taking consideration of currant and wind drift deliberately set my bow off the intended direction by a few degrees, knowing full well I'll be 'heading' towards my intended compass or chart direction. The direction the bow is pointing I would think has little to do with it.

Or am I missing something
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Old 23-03-2015, 17:14   #58
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Re: How Does GPS Work?

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Originally Posted by Rustic Charm View Post
This doesn't sound correct to me. I would think your heading 'is' the direction you want to move the vessel in regardless of where the bow is pointing. I might for example, taking consideration of currant and wind drift deliberately set my bow off the intended direction by a few degrees, knowing full well I'll be 'heading' towards my intended compass or chart direction. The direction the bow is pointing I would think has little to do with it.

Or am I missing something
Rather than guessing or supposing what "heading" means, according to what "sounds correct" to you, I suggest you look it up. It has a precise definition, which is really important for navigation.
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Old 23-03-2015, 17:19   #59
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Re: How Does GPS Work?

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This doesn't sound correct to me. I would think your heading 'is' the direction you want to move the vessel in regardless of where the bow is pointing. I might for example, taking consideration of currant and wind drift deliberately set my bow off the intended direction by a few degrees, knowing full well I'll be 'heading' towards my intended compass or chart direction. The direction the bow is pointing I would think has little to do with it.

Or am I missing something
Well one of us missing something and I'm hoping it's you

Heading is the direction the bow is pointing, any time any where.

The direction of where you want the boat to move to is your course line, sometimes called just course or intended course.

The actual change in postion between two points is your COG (course over ground) or often called "track". I personally prefer the term "track" instead of COG but that maybe because my first formal NAV training was aviation based where the use of track predominates.

FWIW, CTS is course to steer which is the heading you want to use to ensure that your track matches your course line; it may be quite different to your course.
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Old 23-03-2015, 17:51   #60
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Re: How Does GPS Work?

Dockhead: Rather than guessing or supposing what "heading" means, according to what "sounds correct" to you, I suggest you look it up. It has a precise definition, which is really important for navigation.

You have a way with words Dockhead! God help students if you ever attempt to teach in a class room.

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Well one of us missing something and I'm hoping it's you

Heading is the direction the bow is pointing, any time any where.

The direction of where you want the boat to move to is your course line, sometimes called just course or intended course.

The actual change in postion between two points is your COG (course over ground) or often called "track". I personally prefer the term "track" instead of COG but that maybe because my first formal NAV training was aviation based where the use of track predominates.

FWIW, CTS is course to steer which is the heading you want to use to ensure that your track matches your course line; it may be quite different to your course.
I guess (sorry Dockhead, it's a mannerism), that helps to explain it Wotname. As a pilot too I can relate to 'track' and this makes sense of 'heading' being the direction your facing.
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