Example Metadata for GPS Job

Wow, there has been a lot of ink spilt on North Arrows and projection declarations for jobs based on GPS data.

Since I am not a licensed surveyor, my opinion does not count. But I get asked all the time. So here is an example of what I might do as a minimum:

I, Joe Blow, do hereby certify that I am a Professional Land Surveyor, holding 
certificate 99999 as prescribed by the State of Chaos.
I further certify that I have prepared the diagram represented herein and that
the same is an accurate representation of a survey, and was conducted under
my direct supervision.

Benchmark
  The Benchmark for this project is CP201

Coordinate System and Projection Information
  Horizontal Datum = NAD83, North American Datum 1983,
                     2011 Realization 2010.0 Epoch
  GPS Control = Maine DOT Virtual Reference System (VRS)
  Vertical Datum = NAD88, North American Vertical Datum of 1988, 
                   GPS Derived
  GEOID (used for GPS Derived Heights) = GEOID12B (NGS)
  Ellipsoid = GRS1980
  Projection = Maine West NAD83 State Plane Coordinates 
  Distance = US Survey Feet (1 Meter = 3937/1200 US Survey Feet)

Distances
  Distances are Grid distances converted to Ground using a Combined Scale Factor
  The Combined Scale Factor (0.99996067) for this project was derived at
    Control Point 201
          CP201 = 44 2 55.34000 N 69 58 23.05000 W NAD83
          Ellipsoid Height 215.562 ft
          GEOID            -57.100 ft
          Ortho Height     272.662 ft [NAVD88 (Computed using GEOID12B)]

    Example: 9,857.824 SFeet Grid = 9,858.206 SFeet Ground

Bearings
    Bearings are with respect to State Plane Grid North
    Declination at
       TN-SP  0°  8’  4.57”
       TN-MN 15° 36’ 37” (2017 Estimate)

narrow

{My Seal}
Joe Blow
Chaos PLS Number 99999

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Reusing Jobs in One Projection in a New Job with a Different Projection

Let’s assume that we have an .RW5 (Raw File) for a job in one projection (a custom projection) and we want to reuse ‘SOME’ of the coordinates and GPS shots in this job, in a completely NEW job with an alternate projection.

Thesis: I have hundreds of control points and boundary shots for a job that were taken in a custom LDP. Now I want to work on an adjoining site, but in a new projection (or perhaps a standard State Plane Projection.)

If we assign the previous file as the control file of new job with a completely different projection, then we can import the RAW GPS positions to set a base, and we can use the raw data as the GPS coordinates for a localization.

Continue Reading > survce_reusingcoordintesbetweendifferentjobswithdifferentprojections_reva

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Connecting a SP80 Receiver to a NTRIP/DIP Mount Point with Wi-Fi and SurvCE / FAST Survey

The SP80 is billed as ‘the most connected receiver’ and without question, it is.

The internal Wi-Fi transmitter makes it possible to connect a SP80 directly to a Mi-Fi, which reduces the amount of data on the Bluetooth channel.

Let’s look at a comparison between the traditional ‘Data Collector Internet’ (DCI) configuration vs. the SP80 method  [ … sp80-survce_wifi_connection … ]

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Setting the HI in SurvCE for a Focus35 Robot

There are two measure-up indices on a Spectra Precision Focus-30 / Focus-35 Robotic Total Station:

f351

The lower tape hook is for ‘Slant Height’. The top dot & cross is for ‘Vertical Height’.

If you enter a ‘Slant Height’, the data collector shows you the equivalent ‘Vertical Height’:

f352

(Sorry, the picture is faded…to the right of ‘Vertical’ there is a 5.1600) If I measure 4.650′ to the tape hook then SurvCE computes 5.160′ to optical center.

Alternatively I could select the ‘Vertical’ radio option and then enter 5.16 directly.

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Setting Up a Base with Local Coordinates

[ See Also ]

“Okay, I understand that I MUST set my base to a geodetic location that is within 200 meters of my base’s TRUE geodetic location X, Y and Z. But I still want to set the base at a known position and I don’t have a transformation. I swear I can do this in other software packages!”

You can do it in SurvCE also. Here is how.

First go to “Equip: 6 Localization: GPS (tab)”. Set the One Point Azimuth to ‘Geodetic’ or ‘State Plane Grid’ as desired. If you are going to use a system like 1000,1000,0 then you probably want to pick ‘Geodetic’. If you are going to use a state plane or modified state plane coordinate then you undoubtedly want to select ‘State Plane Grid’:

1

Also check to make sure that an appropriate Geoid File is specified. Even if you are in Latin America and have a crappy Geoid file, you STILL need to select it or your elevation error will increase as you move away from the base.

Click on the green check mark to return to the Equip tab.

Do the standard base configuration steps: “Equip: GPS Base: setup Current, COMS, Receiver and RTK tab normally”. Click the Green Checkmark in the upper right corner.

The ‘Base Configuration’ tab is shown. Select the “From Known Position” tab:

2

In my case I want to enter local coordinates 1000, 1000, 0; so I click on the center button ‘Use Local Coordinates’:

3

Enter your desired coordinates, then click on the green check mark. SurvCE will ask you what you want to use for the localization file. The default is the job name with a .LOC extension:

4

Accept or modify the filename, then click on the green check mark.

SurvCE will read an autonomous position from the base. (In the USA this position will be within a couple feet of the IGS08 current epoch true position; elsewhere it will be within 5 meters.)

5

Click on ‘Yes’ to continue.

The base will be configured and SurvCE will ask if you want to store a reference file:

6

Click on ‘Yes’

7

Choose an appropriate name and click on the green check mark.

Your base is now broadcasting corrections and if you could occupy the Base Point (under the base) with your rover, the rover would read ‘1000.00, 1000.00, 0.00’ as you desired.

You are ready to survey, but let’s spend a few extra minutes and address two things:

  • what is going on in the background?
  • how do I setup on this same base point the following day?
  • what if I have more than one rover?

What is Happening in the Background?

First off, SurvCE has done a ‘Read GPS’ and used the autonomous location to initialize the base. The base does not think that it is at 1000, 1000, 0; the base thinks it is at a position that is very close to it’s TRUE position:

8

SurvCE automatically sets up a single point localization. You can view it by going to “Equip: Localization: Points”:

9

Notice that the control point’s local coordinates are the point  that I manually entered. Click on the ‘View’ button:

10

and the corresponding geodetic position is the autonomous (WAAS corrected) base point. This base point is also saved in the .REF file.

So to recap, SurvCE has initialized the base with a ‘Read GPS’ position and then automatically configured a single point localization that results in the base reading the exact local coordinates that I requested.

How do I setup on the Same Base Point on a Following Day?

You want to use the .REF file to insure that the base is initialized with the exact same geodetic position that was used on the first day.

Setup the base over the EXACT same X-Y location as the first day. The HI does not need to match. Enter the correct HI on the ‘Receiver’ tab:

11

When you click on the green check mark, you will go to ‘Base Configuration’ dialog. Select the ‘From Known Position’ tab:

12

Click on the ‘Read From File’ button at the bottom:

13

Select the same reference file that you saved on the first day, then click the green check mark.

SurvCE will check to insure that the broadcast geodetic location is close to the actual location, then display the position read from the file:

14

Click on Yes:

15

And the base is reconfigured exactly as it was the first day. Since you are still using the original job file, the correct localization is automatically used. You are good to survey!

What if I have Multiple Rovers on my Job?

Then you must move the localization file (.LOC) onto each of the other rovers and load it with the load button in ‘Equip: Localization: Points (tab)’:

16

Then select the .LOC which you moved from the first rover data collector:

17

Again, the second rover is now ‘registered’ with the same localization and will follow the first rover’s coordinates exactly.

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Carlson SurvCE Robot Tracking vs. Tracking

Often Carlson SurvCE robotic users are confused by a robot that is tracking the prism while the screen indicates that Tracking is turned off. Here is a screenshot showing tracking disabled:

lt1

You can see that I am “locked” and if I move the prism around, the gun will follow the prism and the AR and ZA on the bottom update continuously:

lt2

But the interface shows that tracking is disabled:

 

lt3.png

If you push this button, then the gun will switch to ‘Tracking’ mode and the icon will change to this:

lt4

Which is ‘Tracking’ ON and the EDM will start firing. And the difference is on the bottom line:

lt5

You now have a slope distance displayed, the gun is firing and making a tracking measurement.

So while we are talking about this, what is the difference between “R” (READ) and “S” (STORE)? Read does a full read, then a store: the gun checks position on the prism, does a couple of precision average shots and then stores the result.

Store just stores the last reading acquired through the tracking process. And there can be a significant difference.

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Setting up a Base in Carlson SurvCE

Over the past few weeks, I have been inundated with calls from experienced users who are setting up GPS bases on sites and blowing the process. [ See also ]

There is a common misconception that you can put any coordinate in the base and have it work well.

These misconceptions are promulgated by  manufacturers who hide automatic localizations behind a magic ‘setup’ curtain. A user can push a few buttons, configure a job at a site and sometimes end up with good coordinates, but they have NO IDEA what is going on in the background. While the underlying true base position and the automatically generated projection and ‘calibration’ can be viewed, most button pressers have no idea what is going on, where to look for the configuration and the magic site calibration ends up existing ONLY in the data collector of the ignorant button pusher.

If you are going to use RTK GPS, you need to explicitly understand what is happening when you configure a base.

I thought that I would write a detailed description of my thoughts on base configuration, but have re-read the Carlson User Manual and found it to be excellent. I have decided to make a few additional notes over the next few days here on the blog.

You can download a PDF copy of the User Manual using this link: [ SurvCE User Manual ]  or from the Carlson Website. The Base Configuration section starts on page 146, is not too difficult of a read, and is an excellent resource.

Let me add these thoughts:

  1. When you configure the Base, your goal is to tell the GNSS base what the actual coordinates for the electrical phase center of the GNSS antenna are, including the actual ellipsoid elevation.This is done by telling SurvCE the position of the Ground Mark. (The point on the ground under the GPS head.)If you specify a projected Grid Coordinate, then SurvCE will convert it to the equvalent Lat/Lon/Height.If you specify the Orthometric Height, SurvCE applies the GEOID and computes an Ellipsoid Elevation.

    Since you have provided the Ground Mark elevation, SurvCE will add the rod height HI (either slant or vertical) and the L1 offset (determined by the antenna model ) which sets the offset from the bottom (or measure up mark) to the electrical phase center of the antenna.

    You give SurvCE the Ground Mark position and SurvCE computes the electrical phase center of the GNSS antenna on top of the pole and sends this Phase Center position to the receiver with a command to ‘Be a Base’ and broadcast corrections.

    This Phase Center position HAS to be within 100 feet X,Y and Z of the TRUE geodetic location. The Phase Center elevation HAS to be ELLIPSOID so you HAVE to load and use a GEOID file if you are going to enter orthometric heights.

    If the position is in error by more than 100 feet then Rovers which are using the Base for corrections probably will not be able to fix, or will fix extremely slowly. Bad base initializations also can have the effect of making the base appear to ‘hang’ — it just can’t compute correctors for the signals that it is receiving to broadcast.

    Even the difference of the Geoid height (typically 30 to 60 feet) will severely hinder the rover’s ability to fix.

  2. I am not going to sugar coat the following statement: “If you are initializing your Base with an Orthometric height then you are crazy.” This is a cardinal sin and it cannot be forgiven.Let me give you an example. Pretend that you are at this location:
    Lat: 40 44 10.22058    State Plane Northing (UT C NAD83): 7437104.68825
    Lon: 111 51 34.19263    State Plane Easting: 1540786.56835
    Ellipsoid Height: 1306.483 M (4,286.353 ft)
    Orthometric Height: 1323.212 M (4,341.238 ft)
    You might incorrectly configure your receiver as shown:
    latlonwrong
    In the screen shot above, the orthometric height is entered as an ellipsoid height. This results in a 55 foot bust in the broadcast position of the base. This will significantly slow down a Rover’s ability to fix.In addition it will result in bad orthometric heights as the distance from the Base to the Rover increases.(The reason the ‘Orthometric’ option is grayed out is no GEOID is loaded or available.)
  3. An important statement in the User Manual is: “When you are starting a new job (no information in the raw RW5 file yet), always use the options in From New Position.”
    fromnewpositionfromknownposition
    That sums it up: if you are starting a new job or series of jobs, always use the ‘From New Position’ tab. If you have coordinates for the base that are accurate, then go ahead and use them using the ‘Enter Lat/Lon’ or ‘Grid System Coordinates’ button.
    Otherwise use the ‘Read GPS’ method of getting an approximate position. (You can always set the base at a random position, Read GPS and then do a localization on the Rover.)If you are reoccupying a base point that you have occupied before, then use the ‘From Known Position’ tab. The most common button is then ‘Read From File’.
  4. The Carlson User Manual says that ‘Read GPS’ will return a position that is accurate in the range of 10 to 100 meters. On modern GPS/GNSS receivers, if the receiver has been turned on and tracking satellites for 5 minutes (and is located in the USA), a read GPS will return coordinates that is within 0.3 meters (1 foot) of the TRUE IGS08 framed location.The IGS08 framed position will be within a couple of meters of the NAD83 position that you probably want.

I am working on a follow-up post

  • Configuring a base at a random point near your control at a job
  • Using a single point calibration to match control on the control point (with the random base)
  • Setting up the Base on the second day at this job

So more on this in a later post. ==> [ See also ]

M

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