GSSI SIR 20, User Manual

Page: 77 / 100

Geophysical Survey Systems, Inc. SIR® 20
Manual
MN92-078 Rev F 71
Matching Your Own GPS/GPR Data
With other GPS units, the match up can be done, but it’s a bit complicated. Here’s how.
First Collect the GPS/GPR Data:
•
Turn on your SIR 20.
•
Plug your GPS unit in the serial port.
•
Follow the steps in the Data Collection Mode window during survey setup.
•
Set your GPS to output NMEA (the standard 0183 version 2.1) at 4800 baud.
•
Set your GPS to start logging track data.
On the Garmin units this means going to the Track menu, turning it on and setting the track
interval (i.e. every 2 seconds or every 10 meters.)
•
Start Data Acquisition:
•
Stop Data Acquisition and Close the file.
GPS Start and Stop positions and times go in the header. In our header, rh_version is set to 2. (see
Addendum A).
So far this is not complicated at all. And since most surveys will require nothing more than these two
begin/end positions, any standard GPS outputting GGA will do this job nicely.
Next Time-Synchronize GPS/GPR files.
But if the survey is along a curve, you will need to work out the GPS position of each scan.
This can be done in Microsoft Visual Basic or with Simulink MatLab to get the two data files together.
Our Binary file extension is *.TMF. The tracklog output of your GPS software will have a unique
extension. (that’s why we prefer the Oziexplorer *.plt file so that all the various GPS’s can output data in
one format).
•
For
Time
based data acquisition.
Match GPS Start/Stop position/time with records in the GPS log.
The scan rate is used to time tag individual scans. You can use the start and end system time to more
accurately determine scan rate.
•
For
Distance
based data acquisition or data with user marks.
Match GPS Start/Stop position/time and file filename.TMF to synchronize marked scans with the
time/position records from the GPS log. Interpolate time/distance data between the marked scans as
necessary.
Please see the protocols listed below in the following Addenda for help on how to extract the
necessary information.
Note:
The G30 data logger is our preferred GPS. We do not have the resources to support all the myriad
GPS products that can be used with the SIR 20. And since we believe the header update and the *.TMF
interface is flexible enough to meet most GPS needs, we offer this technical note as our only assistance
for non-standard use.