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Obtaining Bat Events and Data
The Bat system has been modified from its original AT&T form to output detailed raw data over sockets. SPIRIT provides access to the basic data, so why would you ever want to just get the raw data?
The sockets interface provides access not only to the basic position result (x,y,z,error estimates) but to the raw lateration data - the pulse distance measurements and measured intensities.
You may not want to learn or use the SPIRIT build environment
You may want to reduce any latency in event delivery imposed by the layers of SPIRIT which any position event must traverse.
Where is the Data Then?
The data used to be unicast, but this is now deprecated. If you want to use this, the old protocol is below and should work for the moment (but I'm getting rid of it asap).
The new protocol uses multicast:
Multicast Group: 184.108.40.206 Port: 10256
Connect to this group and you will receive variable-sized messages. There are two events: Bat positions and Bat button presses. They can be distinguished using the 16 byte header of the message you receive:
Bytes C++ Type Description 1 unsigned char Message Version (1 at present) 2 short Event id 1 unsigned char Sequence Number for Bat messages 4 long UNIX time (seconds) 4 long UNIX time (microseconds) 4 n/a Reserved
A bat position has the event ID set to 1 and has the following message structure:
Bytes C++ Type Description 16 n/a Header (see above) 6 unsigned char The Bat ID as six unsigned chars 1 unsigned char The GCG id 5 unsigned char The GCG timestamp as 5 unsigned chars 4 float32 x value of result 4 float32 y value of result 4 float32 z value of result 4 float32 Horizontal plane angle (degrees) 4 float32 Vertical plane angle (degrees) 4 float32 Standard deviation of measurement 4 float32 GDOP value 4 float32 Temperature of room (C) 1 unsigned char Number of accepted pulses (na) 1 unsigned char Number of rejected pulses (nr) 1 unsigned char Number of secondary pulses (ns) na*20 See below Data for accepted pulse measurements nr*20 See below Data for rejected pulse measurements ns*20 See below Data for secondary pulse measurements Varies char array Textual descriptor of the relevant MM ('\0' terminated)
The 20-byte data structure for each pulse is as follows:
Bytes C++ Type Description 4 float32 The x co-ordinate of the receiver 4 float32 The y co-ordinate of the receiver 4 float32 The z co-ordinate of the receiver 4 float32 The pulse ToF as a distance (m) 4 float32 Intensity of received pulse (arbitrary)
A bat button press has the event ID set to 2 and has the following message structure:
Bytes C++ Type Description 16 n/a Header (see above) 6 unsigned char The Bat ID as six unsigned chars 1 unsigned char The GCG id 5 unsigned char The GCG timestamp as 5 unsigned chars 1 unsigned char The button pressed (0=Top, 1=Bottom)
See the BatFeed program. The code for this program can be found in /project/gsp/bat/versions/v3.1/core/src/clients/BatListen/OMMulticastListener.cc