data format

RocketLogger Data (RLD) Format Specification

Data File

The sampled data can be stored either in CSV or in binary RLD format, which is explained below.

Overview

A RLD file consists of a file header and a data structure. The header contains a constant size lead-in, a comment and a list of channel structs, describing all sampled channels. The data part contains a list of data blocks. All blocks are aligned to 32-bit and the data ist saved in Little-Endian.

The following picture shows an overview of the file structure. Red blocks define data, whereras all other colors are only used to show the logic structure.

File Header

Lead-In

The file header lead in contains general measurement information and has a fixed size.

Offset	Size (byte)	Field	Content
0x00	4	Magic Number	%RLD ( = 0x444C5225) magic number (unsigned integer)
0x04	2	File Version	Current file version number (unsigned integer)
0x06	2	Header Length	Total header length in bytes (unsigned integer)
0x08	4	Data Block Size	Data block size in samples (unsigned integer)
0x0C	4	Data Block Count	Number of data blocks (unsigned integer), last block may not be full
0x10	8	Sample Count	Total number of samples taken (unsigned integer)
0x18	2	Sampling Rate	Sampling rate in SPS (unsigned integer)
0x1A	6 x 1	MAC Address	MAC address as device identifier, stored in Big-Endian (unsigned integer)
0x20	8	Start Time Seconds	Start time seconds in UNIX UTC time (unsigned integer)
0x28	8	Start Time Nanoseconds	Start time nanoseconds in UNIX UTC time (unsigned integer)
0x30	4	Comment Length	Length of header comment in bytes (unsigned integer)
0x34	2	Binary Channel Count	Number of binary channels (unsigned integer), nb
0x36	2	Analog Channel Count	Number of analog channels (unsigned integer), na

Total size: 56 bytes

Comment

An additional comment can be put here in ASCII format. Its size is defined in the header lead-in and it is aligned to 32-bit using bit stuffing.

Channels

This part contains detailed information about all sampled channels. There can be an custom number of channels. The channel order determines the channel position in the data block. Each channel can have a different sample size, however it is recommended to have equal sizes for improved import into processing tools (e.g. Matlab).

Offset	Size (byte)	Field	Content
0x00	4	Channel Unit	Encoded channel unit 1 (integer)
0x04	4	Channel Scale	Channel scaling in power of tens, ignored for binary channels (integer)
0x08	2	Data Size	Channel sample size in bytes, ignored for binary channels (unsigned integer)
0x0A	2	Valid Data Link	Link to additional range valid binary channel (unsigned integer)
0x0C	16 x 1	Channel Name	Name of channel (char array)

Total size per channel: 28 bytes

¹ Channel unit codings:

Code	Unit
0	Undefined
1	Voltage
2	Current
3	Binary
4	Range Valid (binary)

Data

The channel data is stored in a list of blocks. Every data block contains a time stamp in UNIX format (UTC) and multiple samples. The binary channels are merged into binary values, right aligned with the first channel at LSB. The number of binary values n_bv is equal to n_bv = ceil(n_b/32).

Data Block			Size	Type
Block 1	Time Stamp	Seconds	8B	Integer
		Nanoseconds	8B	Integer
	Sample 1	Binary Channels	4B	Binary
		Channel A1	Variable	Integer
		...
		Channel An	Variable	Integer
	...
	Sample n	Binary Channels	4B	Binary
		Channel A1	Variable	Integer
		...
		Channel An	Variable	Integer
...
Block n	Time Stamp	Seconds	8B	Integer
		Nanoseconds	8B	Integer
	Sample 1	Binary Channels	4B	Binary
		Channel A1	Variable	Integer
		...
		Channel An	Variable	Integer
	...
	Sample n	Binary Channels	4B	Binary
		Channel A1	Variable	Integer
		...
		Channel An	Variable	Integer