Libelium - Development

Capturing and Storing GPS Data

Meshlium can integrate a GPS receiver which allows to know the exact location of the router any time. It is specially interesting for mobile and vehicular applications and when setting long range links as the GPS position also gives information about the height of each point so the Fresnel Zone can be accurately known.

The GPS module gives us information about:

latitude
longitude
height (meters)
speed (km/h)
number of satellites
date/time

The GPS receiver works with the NMEA mode (National Marine Electronic Association).

The different types of NMEA statements supported by Meshlium are:

NMEA GGA: provides location data and an indicator of data accuracy.
NMEA GSA: provides the status of the satellites the GPS receiver has been connected to.
NMEA GSV: provides information about the satellites the GPS receiver has been connected to.
NMEA RMC: provides information about the date, time, location and speed.
NMEA VTG: provides information about the speed and course of the GPS receiver.

The most important NMEA statements are the GGA statements which provide a validity indicator of the measurement carried out, the RMC statement which provides location, speed and date/time and the GSA statement which provides information about the status of the satellites the GPS receiver has been connected to.

Example of the information read from the GPS:

TimeStamp              Longitude        Latitude     Altitude   Satellites  Speed

2011-04-19 12:52:03    00053.1702,w     4140.8281,n  210.7,m    10          0.2,k

The idea is to capture NMEA sentences in a defined interval which can be configured in order to extract the information given by the GPS.

We can perform three different storage options with the data captured.

Local File System
Local Data Base
External Data Base

Local File System

Steps:

1º- Give a name to create a new file where the GPS data will be saved

2º- Select this file and press the "Select file" button

3º- Set the check box "Store frames in the selected file" and press the "Save" button

From now Meshlium will automatically will capture the GPS frames and it will store the results in this file. This process will also continue after restarting Meshlium.

The file will be created in the folder /mnt/user/gps_data and can be downloaded just selecting it and pressing the "Download" button.

At any time you can see the last "x" lines added to the file. Just set how many lines you want to see and press the "Show data" button.

Local Data Base

Meshlium has a MySQL data base up and running which is used to store locally the information captured. In the "Local Data Base" tab you can see the connection parameters.

Database:       MeshliumDB
Table:          gpsData
IP:             localhost / 10.10.10.1 *Depending on the parameters set in 
                                        the Interfaces section
Port:           3306
User:           root
Password:       libelium2007 *You can change this password see the Users 
                              Manager section

Steps:

1º- Set the check box "Store frames in the local data base" and press the "Save" button

From this time Meshlium will automatically read the GPS frames and will store the results in the Local Data Base. This process will also continue after restarting Meshlium.

At any time you can see the last "x" records stored. Just set how many insertions you want to see and press the "Show data" button.

Important: The Time Stamp info is extracted from the GPS frames not from the system.

External Data Base

Meshlium can also store the information captured in an External Data Base.

Steps:

1º- Pressing the "Show sql script" you will get the code needed to create the data base along with the table and the right privileges.

2º- Insert this code in your MySQL management application.

3º- Fill the Connection Data fields with the information about where the data base is located (IP, Port) and with the authentication options (Database, Table, User, Password).

4º- Now press the "Check Connection" button to see if the configuration is correct

5º- Set the check box "Store frames in the external data base" and press the "Save" button

From this time Meshlium will automatically read the GPS frames and will store the results in the External Data Base. This process will also continue after restarting Meshlium.

At any time you can see the last "x" records stored. Just set how many insertions you want to see and press the "Show data" button.

Show me now!

In the "Show me now!" tab you can see in real time the GPS frames captured.

You can specify if you want the information to be updated periodically with the defined interval just checking the "Use the Defined Interval" button.

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