differential gps processing guide

8/10/2019 Differential GPS Processing Guide

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Differential GPS Processing Guide for Novicesusing Topcon Tools version 7.5 (9/24/2013)

This is a guide for those with either no or little experience processing differential GPS data. It is astep by step guide to using Topcon Tools version 7.5 to process differential GPS data. The steps

will follow this general outline:

1) convert the receiver data files to RINEX2) get the precise base station position3) open Topcon Tools and create a project4) import the base station data5) import the roving station data, repeat for each rover station6) process the baselines7) copy the results to an excel spreadsheet

Eventually you will be collecting your own data to process. To follow along with this guidesexample data from the UW Madison campus, please download the test data. It can bedownloaded from this link:

ftp://ftp.geology.wisc.edu/lord/gps/UWdata.zip

This guide assumes that you have already installed Topcon GPS Office version 7.5 and theTrimble RINEX file conversion utility. If you havent, the following links will be useful.

Topcon GPS Office version 7.5http://facility.unavco.org/kb/questions/22/Processing+Software+Summary+-+Topcon+Tools

Trimble ConvertToRINEXhttp://ww2.trimble.com/trimblerinex_ts.asp

Topcon Tools is a commercial software package which is free to download and can be usedindefinitely in the free demo mode (limited to 5 points at a time). Almost all users doing simple

differential GPS surveys can use the demo mode to process their GPS data. As of spring 2013,the cost of one seat without the demo limitations was $1500.


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1) Convert receiver data to RINEXCopy the base and rover GPS data files onto the computer being used to process the GPS

data. In this example we will assume the base station GPS data is in the folderc:\data\130607b and the rover GPS data is in the folder c:\data\130607r. The general

form is c:\data\YYMMDDb or c:\data\YYMMDDr where YYMMDD is the date of datacollection, b is for base GPS data, and r is for rover GPS data.

We use several models of Trimble GPS receivers and each has different data formats and

file suffixes. Here is a summary:

Trimble receiver model Data file suffix

4000ssi, 4700 .dat

5700 .T00

NetRS .T01

NetR9 .T02

Trimble provides the tool Convert to RINEX to convert any of these files to RINEX.

On the computer desktop, double left click on theTrimble Convert To RINEX icon. The program can also

be found under Start/Programs/Trimble/Convert To

RINEX/Convert To RINEX.

The Convert to RINEX window will open.

Left click on File/Open

Use the Look in: control and/or the Up one

level button to navigate to the Trimble basestation data folder c:\data\130607r.

By default, the window will display .T00, .T01,and .T02 files. If you are processing .dat files,

use the File of type control to show .dat files.

Left click on the first file you want to convert.


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If you want to convert more than one file,

depress the shift key, left click on the last file,and release the shift key.

When you have all the files to convert

selected, left click on the Open button.

The dialog window will disappear andinformation on the selected files will appear.

Left click on File/Convert Files.


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The program will convert the data files to

RINEX format and place the resulting data filesin the same folder as the GPS receiver data

files. You will see files ending in .YYo, .YYn,

.YYm, and .YYr where YY is the last two

digitis of the year.

Repeat the above steps with the base stationGPS data files.

When done, left click on the [X] close button inthe upper right corner.

2) Get the precise base station positionIf the base station position is unknown, there are several free precise positioning web

services available:

OPUS (http://www.ngs.noaa.gov/OPUS/)

AUSPOS (http://www.ga.gov.au/bin/gps.pll )APPS (http://apps.gdgps.net/)

CSRS (http://www.geod.nrcan.gc.ca/products-produits/ppp_e.php )

For this example we will use AUSPOS as it has a simpl use interface and does not require

a user account.

Start a browser and openhttp://www.ga.gov.au/bin/gps.pll

After the page opens, left click on the Browsebutton.


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When the file dialog opens, navigate to the

folder c:\Data\130607b.

Left click on the RINEX obs file (ending in

.YYo), and then left click on the Open button.

Enter the antenna height (0.550 m).

Select TRM41249.00 TZGD as the antenna

type (Trimble Zephyr Geodetic).

Enter your e-mail address.

Left click on submit.

You should see this page acknowledging yourprocessing request.

Wait for the results to show up in your e-mail

(5-15 minutes).

The resulting AUSPOS report is included in the UWweeks.zip data file. The sectioncontaining the station position is below:


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From this we can see the rapid data products solution for the base station is

N 43 deg 04 min 14.18040 sec,W 89 deg 24 min 22.89415 sec,

248.515 m height above ellipsoid.

You can convert DMS to decimal degrees and get

+43.07060567 43 + 04/60 + 14.18040/3600-89.40635949 -(89 + 24/60 + 22.89415/3600)

248.515 m HAE

You should also note that these coordinates are relative to the ellipsoid used by the

EGM2008 geoid. As every geoid and ellipsoid model is different, you should be very

careful when converting coordinates from different datums or geoids to a common geoid

or ellipsoid. For example, you would find significant difference from a map showingNAD27 (North American Datum 1927) or even a GPS handheld showing WGS84

coordinates.

You should also be aware that the precise positioning web services will use the most up

to date reference network data and that the solution 1 day after data collection wont be

the same as a week, or when the final reference data is available after 2 weeks. If you areusing rapid results in the field to check data quality, resubmit your base station data for

reprocessing after two weeks or longer after the data was collected.

3) Open Topcon Tools and create a project

On the computer desktop, double left click on

the Topcon Tools icon. The program can alsobe found under Start/Programs/Topcon/Topcon

tools v7.5.


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A dialog will appear if you do not have a paid

license installed on the computer.

Left click on the Demo Mode button.

A startup window will appear.

If you have already made a QC (quality

control) job, select it, and left click on the

Open job button.

Otherwise, left click on the New job button.

.

Enter QC in the job name box.

Select GPS+ for the Configurations entry.

Left click on the Edit configuration button.


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Left click on Display.

Left click on the Angles tab.

Select ddd.ddd for the Angles and lat,lon

entries.

Left click on Coordinate system.

Left click on the Setup tab.

Select

Datum: WGS84.Coordinate type: Datum Lat, Lon, Ell. H.

Left click on the OK button.

Note: if you are doing very precise geodetic work, and have long baselines, you should

either convert your coordinates to WGS84, or select the datum and coordinate types tomatch your data. The GRS80 ellipsoid and ITRF2008 geoid are not in the default datum

or geoid lists so they would need to be added to get the most accurate results. Using the

incorrect coordinate system will cause a second order error which gets worse for longer

the base to rover baselines.

The job window will appear.

Left click on Job/Save Job so it is available the

next time you use Topcon Tools.

4) Import the base station data


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Navigate to the base station data folder

(c:\data\130607b in this example).

Left click on the first RINEX file. Depress the

Ctrl key, and left click on each remaining

RINEX files associated with that occupation,release the Ctrl key, and left click on the open

button.

The data will be read and will be shown on the

Topcon window. Left click on the new entry inthe name column and add the actual site name.

Under the base station control column, change

the control entry from None to Both. Thisindicates that the base station coordinates are

fixed in both the vertical and horizontal

directions.

If you are in the field without easy internet access and just want to use Topcon Tools tocheck the accuracy of the base-rover relative position, you can leave the coarse position

in the lat, lon, elevation columns for the base station. The accuracy of the base station

location will only be accurate to several meters, but going through the processing stepswill allow you to evaluate if the base and rover data is good.

If you do have the precise coordinates of the base station, left click on the lat, lon, and

elevation entries and change them to the precise values.

5) Import the roving station data, repeat for each rover

station


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.Use the Job/Import menu item.

Navigate to the rover station data folder(c:\data\130607r in this example).

Left click on the first RINEX file. Depress theCtrl key, and left click on each remaining

RINEX files associated with single site, release

the Ctrl key, and left click on the open button.

The data will be read and will be shown on the

Topcon window. Left click on the new entry in

the name column and add the actual site name.

Repeat the Job/Import steps for eachremaining rover site. The demo mode will

allow a base station plus 4 roving sites to be

used in a single job.

6) Process the baselines


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Use the Process/GPS+ PostProcessing menu

item.

All the base-rover baselines will be processed

and the coordinates and error estimates will be

updated.

Left click on the GPS Obs tab.

Evaluate the horizontal and vertical precision

entries for each baseline. They are displayedin meters. Typical values are 5 to20 mm for

baselines from 0 to 10 km. Vertical is

typically 1.5 times the horizontal error..

After loading all the data youll probably want to save the job.

Use the Job/Save Job As menu item and save it with a name line QC130607.

6) Copy the results to an excel spreadsheet

There are three tabs with information you will want to place in a spreadsheet: Points,GPS Occupations, and GPS Obs.

Left click on the Points tab.

Type Ctrl-A to select all the points.

Copy the data by typing Ctrl-C.

Open a blank spreadsheet.

Double left click on the sheet1 tab name and

change it to Points.

Left click on the A1 cell, and type Ctrl-V to

paste the data.


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Left click on the GPS occupations tab.

Type Ctrl-A to select all the points.


Switch to the spreadsheet using Alt-Tab.

Double left click on the sheet2 tab name andchange it to GPS Occupations.

Left click on the A1 cell, and type Ctrl-V topaste the data.

Left click on the GPS Obs tab.

Type Ctrl-A to select all the baselines.


Switch to the spreadsheet using Alt-Tab.

Double left click on the sheet3 tab name and

change it to GPS Obs.

Left click on the A1 cell, and type Ctrl-V to

paste the data.

Use the Excel File/Save As menu item to save the spreadsheet to 130607.xls.

Close the spreadsheet using File/Exit.

Close Topcon Tools using the Job/Exit.

This completes processing the data using Topcon Tools v7.5.

differential gps processing guide

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