Timestamps

[jfalquez]

Set cohesive timestamps throughout devices.. right now there is a mess of device and system times, and some applications make use of one or the other (vicalib in particular).

[dorian3d]

We should make clear the definition of device and system time first , because these terms get fuzzy when you start writing and reading from files.

[jfalquez]

Good idea. Right now as I get it, system_time is the time the data is received at the computer the sensor is connected to.. so the time HAL library receives data.

device_time, if available, is the internal time sensors often have.. usually a counter that starts upon powering on the device.

system_time is more cohesive between sensors, but there of course will be a skew of time between the real sensor reading and the actual time data is received at the computer.

[dorian3d]

That is the definition I had in mind, but it needs further clarification. Consider this case:

1. I use a sensor (e.g. a camera) to collect data that I store in a log file. These data provide a device time (camera dependent) and system time (the computer time given, for example, by hal::Tic()).
2. Now, I read the data with the log reader driver (ProtoReader).

What system time should the ProtoReader yield here?

According to the definition, it must compute the current time again with hal::Tic(). However, this does not seem completely right, because we may want to retrieve the original system timestamps of all the sensors stored in the log file for debugging. Additionally, being completely strict, the sensor time of ProtoReader should be set to the current time too (since the "ProtoReader sensor" is acquiring the data in that moment). We can make an exception here, though.

The behavior of ProtoReader should be consistent with other drivers that read files. It is to say, FileReader and CsvDriver (IMU). Right now:

• Camera ProtoReader and IMU ProtoReader: they return the system and sensor timestamps stored in the log file.
• Camera FileReader: it returns the same system and sensor time (whatever number is encoded in the filename). We may reconsider how to save the timestamps of the images, especially if we need more than one.
• IMU CsvDriver: it returns the system and sensor timestamps stored in the csv file.