Hi C,
Unless I am misreading your text, you appear to have extra digits in the Lat/Lon. ?

$GPRMC,161229.487,A,3723.2475,N,12158.3416,W,0.13,309.62,120598, , *10 [Ref message]
$GNRMC 060512.00 ,A,3150.788156,N,11711.922383,E,0.0,,311019,,,A,V*1B

E

The other query is when you get to the object to the desired point, the controlled object will keep moving on that Track until it is give another Heading, ie: it will over fly the set point. Will that be a problem.?

 

Hi C,
Unless I am misreading your text, you appear to have extra digits in the Lat/Lon. ?

$GPRMC,161229.487,A,3723.2475,N,12158.3416,W,0.13,309.62,120598, , *10 [Ref message]
$GNRMC 060512.00 ,A,3150.788156,N,11711.922383,E,0.0,,311019,,,A,V*1B

E

The other query is when you get to the object to the desired point, the controlled object will keep moving on that Track until it is give another Heading, ie: it will over fly the set point. Will that be a problem.?

Hi E,
Yes, that's an example, I'll change it. Thanks.
C

 

According to the document link in an early response, the $--RMC messages have six digits after the decimal point for both lat and lon.

If I did the math right, that's a resolution of about 2 mm at the equator.

Since that is significantly less than the precision of the fix, the TS is going to have a heck of a time trying to get the remote to move "1 step" since it might move one direction and the next fix might say that it moved in the other direction many steps.

 

According to the document link in an early response, the $--RMC messages have six digits after the decimal point for both lat and lon.

If I did the math right, that's a resolution of about 2 mm at the equator.

Since that is significantly less than the precision of the fix, the TS is going to have a heck of a time trying to get the remote to move "1 step" since it might move one direction and the next fix might say that it moved in the other direction many steps.

Hi W,
I changed the last digit as an example. In reality it would count up very quickly, until the remote moved.
Best accept my guesses for now, as I'm only testing, nothing too dangerous
Remember, I'm only asking which method is best, so your guess would be good.
C.

 

Hi W,
I changed the last digit as an example. In reality it would count up very quickly, until the remote moved.
Best accept my guesses for now, as I'm only testing, nothing too dangerous
Remember, I'm only asking which method is best, so your guess would be good.
C.

Why would it count up at all (other than precision jitter) before the remote moves?

While the document that was linked indicates that there is a set six digits after the decimal point, the reference message posted by Eric would argue that this is not the case.

That is going to cause you problems if you get messages with different numbers of digits in them, because you seem intent on defining "1 step" as being a change of 1 in the last digit.

To me, it seems much more reasonable to want a particular motion of the joystick to translate to a particular motion over the ground, say 10 meters, and then convert that to the lat/lon you want the receiver to give you and have a tolerance that says once it gets within the tolerance distance of that target, it is considered to have arrived.

 

Why would it count up at all (other than precision jitter) before the remote moves?

While the document that was linked indicates that there is a set six digits after the decimal point, the reference message posted by Eric would argue that this is not the case.

That is going to cause you problems if you get messages with different numbers of digits in them, because you seem intent on defining "1 step" as being a change of 1 in the last digit.

To me, it seems much more reasonable to want a particular motion of the joystick to translate to a particular motion over the ground, say 10 meters, and then convert that to the lat/lon you want the receiver to give you and have a tolerance that says once it gets within the tolerance distance of that target, it is considered to have arrived.

Hi W,
Maybe my examples were incorrect.
You are going to far too fast, I am only wanting which method is best. Just guess.
C

 

Hi W,
Maybe my examples were incorrect.
You are going to far too fast, I am only wanting which method is best. Just guess.
C

How can we advise you which method is best when you haven't communicated what it is supposed to be best at? Let alone what your metric is for what would make one method better than another.

 

How can we advise you which method is best when you haven't communicated what it is supposed to be best at? Let alone what your metric is for what would make one method better than another.

Hi W,
Ok, let's leave it for now, until I can clarify my initial question.
Thanks.
C

 

Hi C,
This may help clarify.

A rule of thumb for the Equator, of say 40,000km.

360deg * 60min * 60sec = 1296000secs

40,000,000mtr/1296000sec = 30.864mtr/sec

Example: dd mm.mmmm

Move from, Lat 37 23.2475 to 37 23.2476
Sub the degrees gives, 23.2575 to 23.2476 min
Sub the integer minutes gives, 0.2475 to 0.2476 min
Sub the decimal parts gives =0.0001 min
Convert to seconds 60 * 0.0001min = 0.006sec.

Which means 30.864mtr per sec * 0.006sec = 0.18518 mtrs

E

 

Hi C,
This may help clarify.

A rule of thumb for the Equator, of say 40,000km.

360deg * 60min * 60sec = 1296000secs

40,000,000mtr/1296000sec = 30.864mtr/sec

Example: dd mm.mmmm

Move from, Lat 37 23.2475 to 37 23.2476
Sub the degrees gives, 23.2575 to 23.2476 min
Sub the integer minutes gives, 0.2475 to 0.2476 min
Sub the decimal parts gives =0.0001 min
Convert to seconds 60 * 0.0001min = 0.006sec.

Which means 30.864mtr per sec * 0.006sec = 0.18518 mtrs

E

Hi E,
Yes, that clears a few things. I'll copy/save.
Regarding the different Lat Lon character numbers. In my small world, I was only thinking about 0-90° between equator and the poles, and 0 and 90° W, so wasn't using the first '0' Lon

Regarding which method is best, I've eliminated ECEF shown in #17, as it's not easy to change the CODEs to POLL it. So it's NMEA messages with NSEW, that I assume will have IF ENDIF N or S and E or W.
Onward and upward.
Did you know that NEWS is gathered from N.E.W.S of the globe? Of course you did!
C

 

Hi E,
Yes, that clears a few things. I'll copy/save.
Regarding the different Lat Lon character numbers. In my small world, I was only thinking about 0-90° between equator and the poles, and 0 and 90° W, so wasn't using the first '0' Lon

But in Post #6 you indicated, or at least pretty strongly implied, that you wanted this to work anywhere on the globe. Now you are saying you only want it to work on 1/4 of the globe?

Did you know that NEWS is gathered from N.E.W.S of the globe? Of course you did!

No evidence that this is the case; it is merely an interesting coincidence in English. The earliest claims that it derives from the cardinal directions of the compass were in publications that contained absurd claims as jokes.

What is the purpose of "news"?

To inform you about what is "new".

Pretty easy to see where the word "news" comes from. Sometimes things really are as simple as they appear.

 

But in Post #6 you indicated, or at least pretty strongly implied, that you wanted this to work anywhere on the globe. Now you are saying you only want it to work on 1/4 of the globe?

Hi WB,
I believe that he is referring to +/-90deg limit of the Latitude Coordinate range.

E

 

Hi WB,
I believe that he is referring to +/-90deg limit of the Latitude Coordinate range.

E

Though he addressed latitude and longitude separately: "0-90° between equator and the poles " and "0 and 90° W".

At this point, "a mental slip when typing" and "not understanding what he is working with" seem about equally likely.

 

But in Post #6 you indicated, or at least pretty strongly implied, that you wanted this to work anywhere on the globe. Now you are saying you only want it to work on 1/4 of the globe?



No evidence that this is the case; it is merely an interesting coincidence in English. The earliest claims that it derives from the cardinal directions of the compass were in publications that contained absurd claims as jokes.

What is the purpose of "news"?

To inform you about what is "new".

Pretty easy to see where the word "news" comes from. Sometimes things really are as simple as they appear.

Hi W,
Yes, anywhere in the globe, within site of that BASE station.
My 90x90 Deg was only a simple example of near my location.
C.

 

Hi C,
The other query is when you get to the object to the desired point, the controlled object will keep moving on that Track until it is give another Heading, ie: it will over fly the set point. Will that be a problem.?

Hi E,
When the remote gets to the desired point it will stop.
C

 

How can we advise you which method is best when you haven't communicated what it is supposed to be best at? Let alone what your metric is for what would make one method better than another.

Hi W,
I think I've now figured out the best method, having eliminated ECEF, thanks for your help.
C

 

I am not clear on your question. Are you asking how to convert a DDMM.MMMMMM fix to a D°M'S" fix? Or are you asking how to compare DDMM.M...N/S or E/W fixes to each other when they don't have matching positions relative to the prime meridian and/or equator?

If the latter, are you calculating distance, bearing, something else?

Hi Y,
One minute you lnow something, the next minute you don't!
Regarding the prime meridian. Even though i've discounted the ECEF system (It's rather complicated! ), I still looked into it, and found the prime meridian I've previously straddled at Greenwich, is not where the GPS would change from W to E, it's actually, 102Mtr E.
Cheers, C.

 

Hi Y,
One minute you lnow something, the next minute you don't!
Regarding the prime meridian. Even though i've discounted the ECEF system (It's rather complicated! ), I still looked into it, and found the prime meridian I've previously straddled at Greenwich, is not where the GPS would change from W to E, it's actually, 102Mtr E.
Cheers, C.

The reason for the difference is because the local gravitational field at the Greenwich Observatory doesn't point toward the center of the Earth. It misses it by that 102 meters.

There's a lot of little discrepancies in surveying, stemming form a lot of different causes. One is that, historically, there was no single reference for the entire Earth -- it just wasn't practical. Instead, large regions of land would use local references and measure distances relative to it. In the U.S., this is the Public Land Survey System, but not every place uses it. There are about three dozen initial points, each having a principal meridian and baseline that forms a set of axes with the initial point as the origin. There are lots of opportunities for errors to propagate in this (or any) survey system. Also, the Earth is neither a perfect sphere and the ability to perform accurate surveys improves over time. As a result, periodically the measurement capabilities reach a point that the existing model of the Earth's surface is no longer adequate exploit the improved capabilities and so a new model is developed. By necessity, it is not going to be an exact match to older models, so measurements need to reference which model they are using. The model of the Earth's surface that is used is known as the datum, and a datum that covers the entire planet (such as the WGS-84 datum used by GPS) cannot be as faithful to the local surface quirks that a datum that is only meant to be used locally can. So for local, precision surveying, local datums are often used. Stitching all of these together is not an easy task.

On top of that, the Earth's surface is not static -- it moves. So decisions have to be made regarding when to keep the datum tied to some feature (which could mean that the coordinates of everything else changes when it moves) and when to abandon the tie to that feature and find a new reference to use. These are not only scientific decisions, but are profoundly political and often hotly contested.

One interesting chapter in surveying stemmed from the two different "official" conversions between metric and English customary units. One stated that 1 in = 2.54 cm and the other that 1 m = 39.37 in. These are not quite the same. Surveyors used the latter definition in survey work to translate maps to meters. But the internationally agreed upon standard is the former. As a result, 1 m is actually (about) 39.370079 inches. For most uses, that doesn't matter. But for distances on the size of a continent, it matters. Over a distance of 1000 miles, for instance, the difference between the two is right about ten feet. Doesn't sound like much, unless one survey says you own that gold-filled ten feet of land and the other says you don't.

In the U.S., we have "the four corners", which is the only place where four states (Colorado, Utah, New Mexico, and Arizona) come together. It was legally decreed by Congress to be at 32°N and 37°W (from the Washington Meridian). Teams then went out to survey the borders, setting in monuments as they went. These were placed as best they could with the capabilities of the day. It has since been determined that the location of the four corners is about 1800 feet from where it was intended to be and this results in a legal battle that went all the way to the Supreme Court, which ruled that what Congress intended didn't matter because the all parties, the Federal government, the four states, and the Indian Nations involved, had formally accepted the boundaries as defined by the survey monuments and that they, therefore, were legally binding. As a consequence, none of these boundaries is actually straight, but rather have minor zig-zags as they go from monument to monument.

To further illustrate the intricacies of a global location system, if you were to use the Principal Meridian instead of the Washington Meridian, you'd end up another two miles off. But this isn't so much a measurement error as it is a failure to translate properly from one reference to another.

 

The reason for the difference is because the local gravitational field at the Greenwich Observatory doesn't point toward the center of the Earth. It misses it by that 102 meters.

There's a lot of little discrepancies in surveying, stemming form a lot of different causes. One is that, historically, there was no single reference for the entire Earth -- it just wasn't practical. Instead, large regions of land would use local references and measure distances relative to it. In the U.S., this is the Public Land Survey System, but not every place uses it. There are about three dozen initial points, each having a principal meridian and baseline that forms a set of axes with the initial point as the origin. There are lots of opportunities for errors to propagate in this (or any) survey system. Also, the Earth is neither a perfect sphere and the ability to perform accurate surveys improves over time. As a result, periodically the measurement capabilities reach a point that the existing model of the Earth's surface is no longer adequate exploit the improved capabilities and so a new model is developed. By necessity, it is not going to be an exact match to older models, so measurements need to reference which model they are using. The model of the Earth's surface that is used is known as the datum, and a datum that covers the entire planet (such as the WGS-84 datum used by GPS) cannot be as faithful to the local surface quirks that a datum that is only meant to be used locally can. So for local, precision surveying, local datums are often used. Stitching all of these together is not an easy task.

On top of that, the Earth's surface is not static -- it moves. So decisions have to be made regarding when to keep the datum tied to some feature (which could mean that the coordinates of everything else changes when it moves) and when to abandon the tie to that feature and find a new reference to use. These are not only scientific decisions, but are profoundly political and often hotly contested.

One interesting chapter in surveying stemmed from the two different "official" conversions between metric and English customary units. One stated that 1 in = 2.54 cm and the other that 1 m = 39.37 in. These are not quite the same. Surveyors used the latter definition in survey work to translate maps to meters. But the internationally agreed upon standard is the former. As a result, 1 m is actually (about) 39.370079 inches. For most uses, that doesn't matter. But for distances on the size of a continent, it matters. Over a distance of 1000 miles, for instance, the difference between the two is right about ten feet. Doesn't sound like much, unless one survey says you own that gold-filled ten feet of land and the other says you don't.

In the U.S., we have "the four corners", which is the only place where four states (Colorado, Utah, New Mexico, and Arizona) come together. It was legally decreed by Congress to be at 32°N and 37°W (from the Washington Meridian). Teams then went out to survey the borders, setting in monuments as they went. These were placed as best they could with the capabilities of the day. It has since been determined that the location of the four corners is about 1800 feet from where it was intended to be and this results in a legal battle that went all the way to the Supreme Court, which ruled that what Congress intended didn't matter because the all parties, the Federal government, the four states, and the Indian Nations involved, had formally accepted the boundaries as defined by the survey monuments and that they, therefore, were legally binding. As a consequence, none of these boundaries is actually straight, but rather have minor zig-zags as they go from monument to monument.

To further illustrate the intricacies of a global location system, if you were to use the Principal Meridian instead of the Washington Meridian, you'd end up another two miles off. But this isn't so much a measurement error as it is a failure to translate properly from one reference to another.

Hi W,
Yes, navigation is interesting, also measurement systems in general. I was watching a video about the standard 1Kg, and the lengths they go to for accuracy.
I was thinking about the prime meridian, and I guess that E is slightly heavier than W, so the line has to be offset, for balance?
C

 

Hi W,
Yes, navigation is interesting, also measurement systems in general. I was watching a video about the standard 1Kg, and the lengths they go to for accuracy.
I was thinking about the prime meridian, and I guess that E is slightly heavier than W, so the line has to be offset, for balance?
C

I don't follow what you mean by E being slightly heaver than W.