Hi all,

I live in an area with a fairly high tidal range - thus it is important to ensure correct recording times so that accurate tidal corrections can be made.

I have noticed that some of my recorded SL2 files do not have the correct start times. Im not sure, but is the start time actualy calculated from backtracking from the time that the file was created (which essentialy is the time the logging is stopped). This time seems correct when viewing in windows 7. If I try and change the start time in RM track properties, the end time will then change to the wrong time.

Am I doing something incorrect when recording data on the elite-7?

Thanks for your help.

SL2 files contain time offsets for each record, but no absolute start time. RM looks at the last modified time of the file and calculates a start time by subtracting the time offset of the last record in the file. This doesn't always work because the modified time can sometimes change, which is why it is also possible to change the start time of the track. What issues are you seeing when you do this?

Matt

hi Matt,

some files will work (i.e. if i change the start time in track properties to the correct start time, the end time also corrects itself).

However, some files end up with the wrong end time if i put in the correct start time.

here are some screen captures to show what i mean - time is in the filename.

hi again Matt,

the more i fiddle with the start time in track properties, the more i seem to see some strange occurrences with end times (sometimes when i change the start time, nothing happens with the end time until i change the start time by 2 hours (i.e. end time stays the same if i change start time by 1 hour, but then it changes if i change it by another hour). Weirdly, the end time often changes to a time before my start time.

Can i email you a load of my SL2 files for you to have a look at? all the file 'modified times' that you see in windows 7 file properties seem to be correct (e.g. if i did a 1 hr 30min survey and start time was 13.30, the file modified time is correct - 15:00). Dates are correct in RM (and file properties). Ive tried putting the start time as UTC (i.e. 1 hr before start of survey local BST time).

Not 100%, but it looks like there might be something going wrong with the way RM is handling my time offsets.

cheers
mike

ps - I'm home now, so will get that c-program with data point reduction algorithm up to you in the next few days for you to have a look at.
pps, my elite 7 unit is set up for BST times (as is my laptop running RM). The start time in all my filenames is also BST Could this be something to do with the problem?? As i wrote before, i have tried changing the start time to UTC, but RM still does some weird things with end times.

Hi Mike,
Sounds a bit iffy for sure. Please do share the files - zip them up and upload to Google Drive (or similar) and send a link through to This email address is being protected from spambots. You need JavaScript enabled to view it. . I'll take a look and see if I can work out what is going on..

cheers,
Matt

ok, thanks matt.

just uploading now.

i think 1 of the files might give you some problems as i stopped the elite-7 unit before stopping the logging, but the rest should be full of good data.

I'm out on the boat tomorrow, so will try changing time setting to UTC on the unit and see what happens.

cheers
mike

hi again Matt,

ok, i think I'm getting somewhere, i think the problem was caused by my mistake.

when i imported the files, the global setting was on UTC rather than local. When i changed global settings to local, things got a lot better. start times weren't perfect, but when i went to track properties and changed them to actual start times, the end time was much more realistic.

I guess it might be good to tweak the track properties section for each imported SL2 file to include a 'local' time, rather than just UTC Dublin Edinburgh etc, so that if the user didn't have the global settings correctly defined, they could change them without it causing problems with the end time. Would also be really good if you could indicate the local time (or UTC if specified) on each spot depth as part of the info box that comes up when you click on a 'dot' in the tracks page.

Hopefully though, anyone who has the same problem I have had, will see this post and realise their mistake!

cheers
mike

Hi Mike,
My bad - I should have thought of that. The timezone/UTC thing affects display, but the time itself is stored internally in UTC. The issue here is that when you enter times, the time you enter is treated as local or UTC depending on your global setting, and things probably got even more confusing in your case because for half the year you are in UTC (so it would work either way), and for the rest you aren't.
I'm not entirely convinced of the merits of the UTC/local option, perhaps always showing in local would be less confusing?

Hi again Matt,

something else I'm puzzling about with recorded sl2 times - don't think its related to UTC / local times though .... I sometimes record several different track lines over the same day. Using the elite 7 i create my filename and 'start logging'. When i finish the track, i 'stop logging'. If i then create another file at a later start time, then 'stop logging' later on, RM seems to use the original start time of the first file when i load the files in.

Changing the start time for later files on the same date results in incorrect end times in RM. i think (but not 100% sure) that If the unit is powered down between the file creations, the start / end times seem ok and you can see this, for example, on the 3 files created on 30th july).

All the file 'modified' times are correct for every file in windows. Ive highlighted what i mean in the screen dumps below.

cheers
mike

just to finish off this thread, in case anyone is having the same query. It's related to the way the elite-7 handles times...

the default start times in RM are correct (just ensure the correct timezone is applied ;-) ) and the tidal corrections will be applied at the right times. Gets a bit confusing as the start time shown in RM might not appear the same time as you started logging a particular track (if you do several different tracks without switching the unit off, the start time in RM of each individual track will look like it starts at the start time of your first track).

However, the actual start time of each of your tracks is correct in RM and the tidal correction will be applied correctly (so i have now just left all the tracks with the default RM times). Matt has implemented a great little check in the next release which you can see track point times and tidal corrections. Ive used it with all my track lines and can confirm the correct tidal correction has been applied (Matt hope you don't mind me sharing this info).