DAGR - Defense Advanced GPS Receiver

This is a method based on tracking the carrier phase as a single receiver is moved from one stake to another.  The path between stakes does not need to be along a straight line, but the view to all the satellites being tracked must not be blocked.

Patent Number	Title	Issue date
5021792	System for determining direction or attitude using GPS satellite signals	Jun 4, 1991
5266958	Direction indicating apparatus and method	Nov 30, 1993

This is a system that uses three GPS receivers and three antennas. 
Maybe a future enhancement on the dual receiver method, i.e. 3 Receiver method
The antennas are used:
First in a straight line
Second two of them are interchanged
Third one of them is moved away from the line by the distance between the remaining two.

Patent Number	Title	Issue date
3766556	CHANNEL SWITCHING PHASE - for canceling IF non linearities	Oct 1973
4719469	Direction-determining system - two fast switched antennas and interferometry	Jan 12, 1988
4845502	Direction finding method and apparatus - two antennas on rotating platform are combined in balanced mixer	Jul 4, 1989
4881080	Apparatus for and a method of determining compass headings, Navy - uses two antennas, ant switch and one GPS receiver	Nov 14, 1989

Patent Number	Title	Issue date
5736960	Atomic clock augmented global positioning system receivers and global positioning system incorporating same	Apr 7, 1998
5739786	GPS transfer initialization system	Apr 14, 1998
5757316	Attitude determination utilizing an inertial measurement unit and a plurality of satellite transmitters	May 26, 1998

There are civilian LRFs made for golf and sporting applications with ranges up to about 1 km, most are a fre hundred yards.
Leica Vector IV
Litton Mark VII - 7.3 x 18 day optics, 4 x 50 image intensifier, Nd:YAG laser, eye-safe 1.57 micron Riegl LASERTAPE FG21 - up to 2500 meters
The military LRFs typically have a max range of about 10 km.
AN/GVS-5 (MX-9838) Nd:YAG 1.06 micron) hand held fielded 1980 - Class 4 Non-Eye Safe, only usable in daytime
AN/PVS-6 Mini Eyesafe Laser Infrared Observation Set (MELIOS), only usable in daytime
MLR 30 - 20 km range, 1.064 microns
MLR 40 - 20 km range, 1.54 microns
LH30 - 80 m to 20 km
LH40C - erbium:glass laser, 1.54 microns, built in compass & inclinometer
Leica Geosystems ZVBA
Brashear LP MLRF 100 - 1.54 microns, mounts on personal weapons
AN/PEQ-21B Common Laser Range Finder (CLRF) - similar in magnification and field of view to the M-22 binoculars, built in compass & inclinometer, GPS interface
AN/AAS-37
AN/AAS-38 Nite Hawk
LRM 2500 CI - 2500 m, built in compass & inclinometer
LRB 25,000 25 km - 1.54 micron eye safe,

Lat
Lon
EL:
GS:
TRK:

Select LOAD then pull tape.
LOAD                       QUIT

Note:  to get to the Help menu from the Quick Menu instead of pressing down arrow four times just press up arrow once.

HELP      TAB:[A]
If an arrow key is pressed the focus will jump down into the lower list.
If ENTER is pressed, then up or down arrow the letter after TAB: will increment or decrement and the list will change being centered on the new letter.

Once the correct TAB:Letter has been selected press any arrow key to move the focus to the center of the list of topics.  Now press ENTER and notice that to the left of the current topic an Up and Dn arrows appear.  Now pressing UP or DN arrows scrolls the list.

Pressing PAGE:
RCVR HW STATUS -> RCVR SW STATUS -> CONFIG STATUS -> RCVR HW STATUS

Send To:[com-a] [com-b]
Type:[all] rcvr setup]  [targets]  [submode setup]  [user coord]  [time]  [user dtms]  [units setup]  [sv data]  [mission data]  [all]
SEND               QUIT

Polaris (DAGR) GPS receiver with Turck PKG3M6S90S Cable

Each COM port can be setup to support:
Inputs: ICD-153, Local Area DGPS, NMEA
Outputs: ICD-153, NMEA

Azimuth Determination, North Finding, Survey Mode (mil speak: Gun Laying System)

Once in the AZ Determination page proceed as follows:
4AK = 4 Arrow Keys

• Press Menu and scroll to Create New, press Enter
• With the name highlighted, press Enter and 4AK select the letters and numbers for you chosen name then 4AK to move to SAVE and press enter.
• With the Walk Time highlighted press Enter, 4AK to set between 1 and 180 seconds, then press Enter
• The display will ask you to press Enter to start the process.  (Prior to this the receiver should have been in Continuous mode and locked on a number of satellites, but if not then you will need to wait here).  You can't start until at least 4 satellites are being tracked, more is much better because while you are walking you may loose some and if the total number goes below 4 then you need to start over.
• After you are stratified with the number of starting satellites press Enter and the display will switch to the walk time count.
• Walk to the second point and when in position press Enter while holding the receiver still, it will take maybe 5 to 10 seconds to determine position 2.
• When it's down press the down arrow to proceed.
• The data defaults to military units.  Changing the units in the main Menu does not effect this page, so 4AK highlight each field press Enter, and select which units to change, for example the bearing change to degrees and the reference change to True, distance in Miles and feet, etc.
  The first result window shows:
• Single Receiver Method (I think you need to connect a second receiver in order for this to change, it's not a menu choice)
  
• Azimuth: 62.29 deg True
• Back Azimuth: 242.29 deg True
• Range 47.02 Feet (0.01 feet is approximately 1/8 Inch!)
• Estimated Azimuth Error: +/- 000.49 deg.
• Press the down arrow to move to Point 1 Information
  
• 10 S     405008 East
  
•              37905 North
• 988 Ft MSL
• Press the down arrow to move to Point 2 Information
• 10 S   485021 East
•          443379 North
• 987 Ft MSL

Questions:
Is it better to carry the receiver so the LCD is vertical or should the LCD be level? LCD level both for compass and GPS reception.
Where inside the receiver is the internal antenna located? just above the LCD.

Thoughts
Using a choke ring antenna would prevent multipath and so you would not loose as many satellites.  Once one looses lock it is removed from the solution because after it relocks the cycle count is no longer valid.
17 Apr 2009

Zero Baseline Testing Single Receiver Method

A way to test the accuracy of the azimuth determination system is to NOT move the antenna.  In this case the roof top GPS antenna was used for both the first and second positions.  If the Azimuth Determination procedure is run using a fixed antenna the result should be a distance of zero with an arbitrary angle.  Things that can be varied are the receiver mask angle.  Zero degrees increases the number of SVs but also allows for more multipath errors.  It’s also location dependant.  The walk time is controlled by making the setting greater than the actual time and then pressing ENTER at the desired test time.  Note there is no display in the results that will tell you the actual walk time so there’s a few seconds of error in the estimate of the actual walk time.  The number of SVs can be controlled to a small extent by when the test is run since the satellite configuration changes with in a 12 hour cycle.

The Walk Time input for the single receiver method just sets the maximum allowed walk time, so it's best to just use two up arrow presses to set it to 180 seconds.  The actual second measurement is made when  you press ENTER at the second location.  My guess is that when the ENTER is pressed the first time the DAGR starts logging carrier phase data.  When ENTER is pressed the second time the DAGR does the calculations involving processing the logged data.  So the time it takes to process the data depends on the actual walk time and is very close to half that time.  For example if the walk time was 2 minutes it will take 1 minute to process the data.

Plot of Range error in Inches vs. Walk time in Seconds

What's not shown is the number of SVs used for the solution.  When the test is started there may be 8 to 10 SVs being tracked, but once any of them drop out they can not be used in the solution so it's not uncommon to loose one or two sattelites by the time the test has finished.   Maybe because of the change in number of SVs and/or different DOPs the test results are not easy to nail down, but you can see there's a definate relationship
 between walk time and accuracy.  A very rough rule of thumb might be:
Accuracy (Inches) = Walk Time (Seconds) / 20
For example at 20 seconds the accuracy varies from 1/2 Inch to 2 Inches.
At 60 seconds it varies from slightly more than 2 Inches to slightly more than 5 Inches.
The accuracy seems to get better than the rule of thumb when the walk time exceeds 2 minutes.  I'm not sure of this is real, or not?
The problem with trying to use walk times near 180 seconds is that the DAGR aborts the measurement at 180 seconds instead of making a measurement.  It's impossible to have a walk time of more than about 175 seconds because the pressing of ENTER has some time delay before it stops the test.

So for the single receiver method the possible angle accuracy depends on how quickly you can move the DAGR while not blocking any SVs.  These are just calculations that have not yet been tested.

If normal walking speed is three miles per hour (4 feet per second), then after 180 seconds the baseline would be a little under 800 feet (241 meters).  An error of 9 inches in 792 feet is 0.054 deg (3.26 arc min) or 0.96 Mils.
 
If a running person traveled at 8 miles per hour (12 feet per second) then at 180 seconds the angle would be 9/25344 or 0.0198 deg or 0.35 Mils.
 
If a car averaging 30 miles per hour moved the receiver and the test lasted 2 minutes the expected accuracy might be 0.0054 deg or 0.096 Mils.

Survey Equipment to support Single Receiver Azimuth Determination

SECO makes a number of poles used to sup[port either GPS antennas or prisim retro reflectors that are suitable for this application and have some very handy features.  Since minimuzing the walk time is important a system where the antenna is just plugged in rather than locted is important.  Although SECO makes a number of clamps to hold survey data collectors they don't have anything that's DAGR specific so I'm going to try and modify one of their plain pole clamps to allow the stock DAGR mounting bracket to be attached.  (13 April 2009)

Part of Azimuth Determination Setup

The Pole and bipod are standard SECO (Survey Equipment Co) items.  This is a very modular system where all the pole sections have 5/8-11 female threads on both ends.

A friction clamp is holding the DAGR standard mount with a 10-32 screw and flat washer making the connection.  The left mounting hole in the DAGR mount is used so that the back connector area is clear of the pole.

Just below the DAGR there is a circular bubble level (black object to left of pole).

Just below the bubble level is a quick disconnect fitting.  The black pole is attached to the pole above and can be lifted off the lower pole.

The lower pole is fitted with the bipod.  The upper part of both bipod legs has a lever actuated length adjustment to allow easy plumbing of the pole.

Rather than spend a lot to get another of these pole setups, I just got a male quick connect pin with a 5/8-11 female thread to put on top of my existing surveying tripod for the second location.

The pole plus bipod arrangement has an advantage over a tripod in that the distance between the GPS antenna and the mark on the ground is a fixed distance.  That's not the case with a tripod.

This setup breaks down to a much shorter length and fits into a carry bag.

DOP Planning

Yesterday (17 Apr 09) there were 7 satellites being tracked but after moving the receiver 33 paces away and returning to the pole the error message was poor satellite geometry.  So some planning needs to be done before hand to chose a time when the geometry is good.  Trimble has a free program called "Planning" to do this. 
Trimble Planning Software Downloads -
They also have a web page where you can get current GPS data.
GPS Data Resources - Almanac files

Outdoor Zero Base Line Walk

21 Apr 2009 - Choose 11:45 to 12:05 window and tried two walks. 
The first for about 2 minutes resulted in a no solution, poor DOP message.
The second for about 1 minute resulted in a distance error of about 4 inches.

28 Apr 2009- It's straight forward to modify the  987-5006-001 mount by adding SECO p/n: 103868-005 and the associated 1/8 x 7/16 spring pin and 1/4-20x1/2 cap screw.  Then it plugs into the p/n 5198-052 Pole Clamp and can be adjusted for tilt.  You can just see the spring pin below the quick release pin on the mount that mates with one of the the small holes on the pole clamp.

Time Display

The DAGR / Polaris Guide POSition page, when scrolled down, shows the current time and date.  But, the displayed time is often in error by 1 second.  This is in my opinion a bug in the Rockwell Collins firmware.  All my other receivers that display time have the seconds change at the UTC second boundry.  The Trimble Scoutmaster even displays the tenths of a second correctly, see image below.
The Polaris Guide (DAGR) is showing the time as 0852:00 but the time is really 0852:01.0 as shown on the Trimble Scoutmaster to the right.

An interisting thing about the Scoutmaster display is that the date is shown as:

WED 06 Sep89

That's off by 1024 weeks, i.e. the GPS week rollover problem.
I wonder what the DAGR/Polaris Guide will show in 20+ years?

Internal Magnetic Compass

The Internal Magnetic Compass does not have tilt compensation.  The compass can be found at <press and hold POS> then <down arrow> to see the compass (you may need to press Enter and arrow keys to highlight the compass, the Enter and activate it since the normal mode is not continous operation).  I found that the first calibration was no longer working by turning in a circle and noting that the display did NOT show the expected 0 to 359.9 deg range but instead showed numbers around 160 degrees plus or minus maybe 30 degrees.  After a simple calibration it was working fine.

To check for tilt:
Face magnetic North (or magnetic South) and tilt up or down about 10 degrees and note the change in reported bearing is only a few degrees.
While holding the receiver level, Face magnetic East (or magnetic West) then tilt up or down about 10 degrees.  This causes about a 10 degree error in the bearing because there is no internal tilt compensation.

The Suunto Vector wrist instrument has a bubble level (just above the 7 in 337) on it's face to aid in holding it level.
The small rectangle in the upper left is the barometric pressure history.
"N" for North which is the closest of the three letter compass points.
337 degrees magnetic bearing.
The black bar below the bearing has a band at the right end below COMP for compass mode.
The modes are left to right: Time, Alti, Baro, Comp
3:57 local time.
On the very outer circumference at the top is a single black tick.  Opposite it are three ticks.  These form a North pointing arrow.
The Bezel was set to the local magnetic devation years ago and you will see that the North Arrow is pointing very close to the "N" on the bezel.   So the line from 6:00 to 12:00 is pointing close to True North.

See: Experiment Relating to the Vertical Component of the Earth's Field for a similar experiment to that above for the Polaris/DAGR.

When MENU is pressed (from any of the Position pages) one of the choices is Select Op Mode.  The choices are:
Continuous -a new fix each second
Standby - no satellite tracking to conservi battery power, but data input and all other operations can be done
Fix - get a single fix then go into Standby

Average -

Time Only - all the effort is put into getting the time BUT in any mode the time display can be off by 1 second.  i.e. you don't  know the time to a second.

Commercial Joint Mapping Toolkit (C/JMTK) ArcObjects software
National Geospatial-Intelligence Agency  (NGA) map data
Support of raster maps: Compressed Arc Digitized Raster Graphics CADRG) and
                                        Controlled Image Base in C/JMTK