On 2014-04-07 11:59, Rainer Mohr wrote:
Am 07.04.14 11:42, schrieb Jef Driesen:
I'm not sure if you are aware of this, but there are dive computers
out there that don't have a fixed sample rate. Some (older) Oceanics
support a depth based sample rate. They record a new sample whenever a
certain depth threshold is exceeded. The timestamps of such samples
are not regularly spaced.
True, the smarttrak data format also has a "repeat x times" if the
depth does not change IIRC
Fact is though, that until today, every DC data format that I have an
import for does give me regular samples inside their own format, even
if the computer does not specifically record one (except for the
Smarttrak format, where i create x dummy samples for the "repeat x
times").
if there is need for irregular sample intervals, I will be happy to
adapt
Technically, the Uwated sample interval is still regular. Omitting
samples where nothing has changed is basically some simple form of data
compression technique to reduce the amount of storage. After
decompressing the data again, you end up with evenly spaced samples
again. That's what libdivecomputer does internally for the Uwatecs.
For the Oceanics the situation is a bit different. It's a real event
based mechanism, without a base sample rate (like the 4s used by the
Uwatecs), at least not that I know about. To make things worse, is that
the resolution of the recorded timestamp is only 1 minute. The result is
that you can end up with zero or more values per minute. Currently
libdivecomputer tries to spread those evenly within that minute. Far
from perfect, but it does result in something reasonable. Multiple
values with the same timestamps is probably even more confusing for
applications. But the consequence is that the sample interval is
variable.
I can provide some data if you want to have a look.
Jef
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