GPSlug
-
Posts
388 -
Joined
-
Last visited
Posts posted by GPSlug
-
-
It's pointless.
-
My WAG: Jericho and Seville
-
There's no ambiguity in how DOP is calculated, but there is in how it translates into error. Just scaling the DOP is making an assumption that all the ranges have the same level of error and are weighted the same in the position solution.There is no ambiguity with DOP. In a perfect world it's 1 (one), but in reality always more. The error estimated from the signal quality should be multiplied with DOP to get the real error.
A more representative error, like the EPE, takes into account that you weight the ranges differently based on the estimated error provided in the ephemeris (or SBAS corrections), the elevation (atmospheric models have more error on low satellites and multipath is more likely), signal strength, etc. Whether it's a 50% number or whatever, the estimated error can be calculated differently for different receivers because of the assumptions made about the external errors and the quality of the tracking chip and antenna.
The hardest error to model is multipath. I generally assume that with no reflectors around, the EPE is probably conservative, and I trust it less and less the more possibility there is for multipath or, worse, pure reflected signals where the direct signal is blocked.
I think the biggest part of the EPE calculation being "proprietary" is that they don't want consumers or reviewers to be able to test it too closely and give them grief when they weren't able to estimate it well, or to give fuel to their competitors who would make comparisons, fairly or unfairly.
-
WAAS removes the the intentional errors inserted into the GPS signal. The WAAS correction is transmitted from 25 ground station across the US and is only available in the US. It does not amplify the signal or change the sensitivity of the GPSr unit. It's that simple.
There is no relationship between WAAS and the military's (no longer used) Selective Availability program.
Well, to be fair to johnling, WAAS was designed for removing SA as well as the unintentional orbit, clock and iono errors. The amount of correction it can handle is much bigger than it needs now, and actually could get better accuracy if it was redesigned with higher resolution with no SA. But it's also more designed for integrity than it is for accuracy, so that won't be enough of a priority to develop and re-certify new messages.
Of course StarBrand is right.
It's just that us possessive capitalist Americans, who invented both GPS and SBAS, tend to call the augmentation system, all of them WAAS instead of SBAS which they technically really are.
IIRC, "WAAS" was coined first and spread around the industry when that was all there was and only later the generalized term "SBAS" was coined to also encompass other systems built on the same standards. Just like "GPS" was generalized to "GNSS" to encompass all the Global Navigation Satellite Systems. I guess it's kind of like using the most popular name brand, like "Kleenex"
.Does anyone, perhaps DENelson83, have the actual coordinates for the 'well surveyed' ground stations for the American WAAS stations? I've seen maps of them, I've seen lists that are not complete, some don't list 25 and some don't list 38 but slightly smaller numbers, and not very precise coordinates if I remember right.
P.S. If you are not within the 5x5 degree grid covered by a ground station, you sight get some WAAS, oops there I go again I mean SBAS corrections. You might get the Fast and the Long corrections but you will not get the Iono corrections.
You've probably seen this map. The coordinates aren't really relevant. It's called Wide Area for a reason. Local effects around the stations get washed out when adjusted into the system-wide model, so it doesn't really matter how far you are from an individual station.
The ionosphere is modeled as grid points on a big shell high up in the atmosphere. To get the correction, the receiver calculates where its line of sight to a satellite will pierce that shell and interpolates between the grid points. If your pierce point is in the grid, you can make an iono correction. It's just that at the edges of the grid, it won't be as good. See here where the GIVE indicates the accuracy of the correction for different parts of the grid. The dots represent where your pierce points are, rather than your location. So near the edge, where you're likely outside the reference station network, you may have some satellites in the good part, some in the not so good part, and some outside. You have to weight the ranges differently and account for a possible bias on the uncorrected satellites, but you can still use the corrections.
-
Whatever app you are using will be getting the data over bluetooth in NMEA format. If your app will show you that data directly or log it to a file, look at the GPGGA message. It will look something like this:
$GPGGA,145109.00,5106.9814,N,11402.2913,W,2,11,1.0,1065.08,M,-16.90,M,11,0100*65
That 2 is the quality indicator, which will be 0 for no fix, 1 for standalone GPS, and most likely 2 for WAAS.
-
Well I'd guess it something to do with Selective Availability and when it was turned off.
from http://geography.about.com
"If you take a look at your handheld or automobile Global Positioning System (GPS) unit today, you'll notice that it's much, much more accurate now than it was on May 1. The reason? U.S. President Bill Clinton ordered Selective Availability (SA) turned off at midnight May 1 (Coordinated Universal Time). Now, civilian GPS users around the world will no longer experience the up to 100 meter (approximate 300 feet) random errors that SA added to keep GPS a more powerful tool for the military. Today, GPS units are accurate to within 20 meters (approximately 60 feet); although in good conditions, units should display an error of less than 10 meters."
Yep. That's right.
When the word went out that SA was being set to zero that night, I started collecting data to capture it happening. The blue line is the horizontal position error. The pink line is the estimated standard deviation, somewhat analogous to Garmin's EPE.
One of the things that the standard deviation is based on is the User Range Accuracy broadcast by each satellite, which gives the receiver an estimate of how much error there will be on the range measurement from the orbit and clock errors on that satellite.
So you can see that 4:00 UTC, new ephemerides were being used that had the artificial errors removed, but they didn't change the URAs in the broadcast right away. This was probably to give some time to verify that everything went right.
Then at 8:00 UTC, the new ephemerides at that time had the URAs lowered to reflect the new level of accuracy, and the estimated standard deviation snapped down. The next day, geocaching was born.
Here's a position plot of the same time.
On to you, Ducky.
-
Another day, another hint.
You wouldn't be in the Geopub today if it weren't for this event.
The answer can be found on geocaching.com. You don't even need to look in any cache listings.
-
Time for more hints.
It's not anything seismic, it's just that the y-axis represents position. Sorry if I led you down the wrong path there. I would not want to be on any planet where the quakes last for hours and move you 70 metres.
So it's not about the ground moving, but this event did make the ground speak.
-
Any company with survey quality receivers will have a lower product line for GIS - Trimble, Topcon, Leica, Sokkia, Magellan, etc. So if your broader organization has some of this stuff already, you might want to get the same kind just for simplicity if you want to share equipment or software packages. It might get you a better price from the dealer too.
Magellan's professional products are practically a different company. At least in terms of product lineage. Thales bought both Magellan and Ashtech and combined them under the Magellan name.Yes, But I'd avoid Magellan at all costs. But I imagine that their Professional GIS products are professionally supported LOL.
Survey equipment is generally more accurate than what the military uses. No license involved.After all you have to spend really big bucks for any military P-code capable receiver, and be licensed also. -
Here's a revised plot with a few more clues.
-
Without logging to the data card turned on, the active tracks will be stored in the internal memory. When they get to 10,000 points, it will start deleting the older points so that you have the last 10,000 points.
When you turn on logging to the data card, it still saves the active tracks to internal memory the same way. But it also stores them to the data card as one GPX file, which may contain multiple tracks, per day. This will keep all your tracks, presumably until the memory card is full. But compared to map data, they don't take up much space at all.
But note that when you download tracks into MapSource, it's only getting the active tracks which max out at 10,000 points. To get the data card tracks, you need to set it as a USB mass storage device or use a card reader.
I think the main benefit is that, even if you are away from a computer for an extended time and hit the maximum, you can still retrieve all your tracks.
-
No right answers yet, except for the fact that the x-axis is time. And Tethys C is in the ballpark for the y-axis.
-
That number for width of 6° is wrong. (Well, I guess it is right taken literally in that it is never more that 674,000 meters.)
The semi-major axis of the WGS84 ellipsoid is 6,378,137 meters, which means that 6° of longitude at the equator is 667,917 meters and the max Easting is under 833,959.
-
OK, here goes.
What does this image represent?
-
Since the 1 Millionth waypoint ID was recently issued
Of the major milestone waypoint IDs issued (i.e. 100K, 200K, 300K, etc.) only two of them have been outside of the United States - Which Two, and in which country/Countries are they in? For bonus points, Which one(s) is/are archived?
Is this the question in play now?
Here's what I have, getting the GC codes from FizzyCalc.
- 100000 (GCH4VQ), active in Indiana, United States
- 200000 (GCMFXH), archived in Texas, United States
- 300000 (GCQVZB), active in Arizona, United States
- 400000 (GCW715), active in Kentucky, United States
- 500000 (GCZJ2Z), active in Netherlands
- 600000 (GC12Y4R), active in New Hampshire, United States
- 700000 (GC1696J), active in Pennsylvania, United States
- 800000 (GC19M8C), active in Sachsen, Germany
- 900000 (GC1D0A6), active in California, United States
- 1000000 (GC1GBC0), active in Connecticut, United States
- 100000 (GCH4VQ), active in Indiana, United States
-
So are you just reading the GPX as a text file on the PDA?
There are a number of applications you could use to interpret that data for you in a more friendly way (CacheMate, GPXSonar, GPXView, etc). I'm not sure which would work best on an Axim X5, though.
-
I'll make a guess. Iron Oxide?
-
To answer your missing but likely question, yes.
-
Binrat is my bother
Dr. Freud. Paging Dr. Freud. Please report to the Canadian Geopub Quiz.
-
My setup is a little different. I have a third-party($) "custom action" in the rules wizard that will save attachments to a folder and run an executable. My executable in this case is a perl script that starts GSAK with a macro to load the PQ. So as long as Outlook is running, as soon as the PQ comes in GSAK will immediately have the latest. I can provide details if you're interested.
As for your problem, I don't really do Visual Basic and I'm not sure if this would be a problem in its syntax, but could it be the space in your file path causing your headaches.?
-
I heard rumors that an upcoming model will record your "state of mind" with each data point in the track log.
That would actually be pretty easy to do. Just make it beep really loudly at each data point and record the state of mind as rising levels of irritation.
-
Does it work to put another zero in front of your longitude? Like "001 23.456"?
-
Are you able to tell if the vertical errors are consistently up or consistently down, as if it always shortens or always lengthens some of the ranges?
On another note, has anyone tried, instead of power-off/power-on, to just completely block the signal for a second or two to see if the position fixes itself? I mean like stick it in an ammo can or mylar bag or underwater (with protection considering the waterproofness complaints).
-
My local Army Surplus guy tells me that a military GPS can put you within a foot of your target. He also says that those GPS units aren't just available to anyone.
Cheers
Mark
That's pre-S/A-set-to-zero thinking. Military receivers aren't any more accurate than commercial and scientific units.
What they have instead is the ability to still acquire and track while they're jamming the civil codes.
.
They Finally Did It
in Canada
Posted
I've been told that in Alberta (and it's probably in most other places too) you can be cited with a catch-all "driving with undue care" for electronics handling, putting on make-up, performing taxidermy, or whatever. But it generally is only as an add-on to other offences, e.g. after you've already hit the pole. It would be too easy to fight on it's own.