Magellan MobileMapper 6 GPS – Part 3

In part 2 of the MobileMapper instructions we collected data in the field. Now we are going to move our data from the Magellan to the PC and post-process it to improve spatial accuracy.

Move data from the Magellan to the PC

On your PC/Laptop you should have a designated folder for your GIS/GPS work, say C:\dissertation\GIS. If such a folder does not exist, create it.

• If your PC has an SD Card reader:
  1. take the SD card out of the Magellan and put it in your card reader.
  2. Using Windows Explorer, navigate to the SD Card.
  3. Here you will find
     • a folder with your name, containing the shapefiles you edited in the field, e.g. samplesites.* and the map file you created for the fieldwork, e.g.  karl260609.map.
     • a folder GPS Raw Data containing the raw GPS data data needed for post-processing.
  4. Move both folders from the storage card to your PC, e.g. to C:\dissertation\GIS.
  5. Put the SD card back into the Magellan.
• If your PC/Laptop does not have an SD Card reader:
  1. In a previous step you should have installed Microsoft Active Sync (Win XP) or Windows Mobile Device Center (Vista) If you have not installed it yet, install it now. The following steps assume XP.
  2. Connect the Magellan to your PC with the USB cable and switch it on.
  3. Using Windows Explorer, navigate to My Computer > Mobile Device > My Windows Mobile-Based Device > Storage Card.
  4. Here you will find
     • a folder with your name, containing the shapefiles you edited in the field, e.g. samplesites.* and the map file you created for the fieldwork, e.g.  karl260609.map.
     • a folder GPS Raw Data containing the raw GPS data data needed for post-processing.
  5. Move both folders from the storage card to your PC, e.g. to C:\dissertation\GIS.
  6. Disconnect the Magellan.

Install post-processing software

We post-process our data using a software tool called MobileMapper Office. If this software is not installed on your PC, install it now:

1. Download the MobileMapper software from Magellan and extract it to your local drive (e.g. to the Desktop). This creates a folder Mobile Mapping v2.0 CD.
2. Open the folder Mobile Mapping v2.0 CD and double-click setup.exe
3. From the menu select the option Install MobileMapper 6 Office 1.0.
4. Accept all defaults.
5. After installation completes, MobileMapper Office launches automatically. Cancel and close it for now.

Get post-processing reference data

In short, post-processing compares the data you collected in the field to reference data from a GPS base stations and adjusts your data accordingly.

For locations in the UK we use RINEX reference data, provided by Ordnance Survey (OS). For information on RINEX see the OS website.

1. Go to http://gps.ordnancesurvey.co.uk/active.asp, search for the RINEX data corresponds to your survey and click Process.
2. On the next page download your RINEX data. It comes as a ZIP file.  Extract it, e.g. to C:\dissertation\GIS\RINEX. This creates two files for each reference station seletced.

Post-process

1. Go to Start > All Programs > Magellan > Mobile Mapper 6 Office
2. Load the data you collected in the field:
   1. Click the top left blue button and select Open.
   1. Select the map you were using in the field, e.g. C:\dissertation\GIS\karl260609.map. This loads the map into the display as it was on the MobileMapper device.
3. Load the raw GPS data:
   1. This raw GPS data was recorded by the Mobile Mapper device along with your features. This is the data that will actually be processed. Click Add Rover Raw Data and select your raw data file, e.g. C:\dissertation\GIS\526209071000.grw.
   2. The raw data file is loaded and listed in the bottom table.
4. Load the RINEX reference data:
   1. Click Add Reference Raw Data > From File and select the RINEX data you downloaded, e.g. C:\dissertation\GIS\MANH191q.09o.
   2. The reference data file is loaded and listed in the bottom table.
   3. Repeat until all reference files are loaded.
5. Click Start Processing.
6. When processing finishes, the application automatically shows the corrected features. The original features are copied to a backup file, e.g. samplesites_bak.shp.

Done! According to Magellan, with post-processing the accuracy of your features is 1-2m in X and Y. In practive I found it to be even better.