Saguday is going to become a survey vessel

[smartcom]

Tidal corrections

Getting the tidal corrections right is taking a bit of time, but we're almost there.
We create a mesh around all the tidal stations - you can see it here http://www.teamsurv.eu/devtools/tidal_stations.html at the moment, though this is an internal document so won't always be there - and then use this as the basis of interpolation. This was initially generated automatically, and is then tweaked manually, and we're almost there. (Ignore the high latitudes and the 180 meridian, they are outside of our current area).
Then for each point we take the position and time, look up the tide heights for the polygon the vessel is in, and apply the interpolation. We have tide heights for each station calculated at 10 minute intervals using our TideWizard engine.
For the 1st release we're just using the tidal station data for the polygon the boat is in, but later we'll rerun things using an interpolation, to avoid jumps at the edges.
Tim

Umm, yes. I have been in touch and I must admit I haven't sent any data yet. I don't have one of their loggers as I have some software on this laptop which already does that. They also provide software if you can import NMEA data into the laptop. I do need to tidy up my files for them and I promise myself to get round to it but I am in the middle of a chartlet of the Nass - why I'm not sure, three quarters of the way through one of Lawling Creek, need to redo my one of the Ray Sand using better Lat/Long ratios (the old one is square). You prompt me to make sure I sort my files out when I get back on Tuesday.

I am a little intrigued about how they are going to reduce all this data to a Chart Datum. I know the plan is to start using predicted data and then go onto actual (You can rest assured that I have been using actual data for my chartlets - makes a difference of less than an enormous 2 to 3 inches in most occasions!) Having done it for rather small areas has opened my eyes to the enormity of the work, particularly in the Thames Estuary. It's not too bad when you are doing say a point across the Sunk Sand, a relatively narrow geographic area. For example when I got to the Barrow No what ever it was and when back over the sands towards the Black Deep, it was small enough an area to assume that I could use one interpolation on Sheerness that could be applied for the whole area and I just had to adjust the height of tide for the time it took me to go back and forth. But that journey includes data from Mersea Quarters, out into the Blackwater, down to and across the Spitway, across the Swin, round the East Barrow and across the Barrow Deep as well as the sands. Applying height of tide corrections for that whole journey strikes me as quite a challenge! And an impressive thing to do.

There is at least one other ECF forumite sending data - the forumite who has been working on the Gunfleet wind farm, forgive me, can't remember his name.

 

[tillergirl]

That's interesting Tim, thanks. Just back from abroad so I will get round to sending you my data.

I think the polygons are a little large but then I have had the advantage of doing set spots and not the problem of near continuous interpolation.

 

[tillergirl]

I'd like to join in but don't have a chart plotter. Thanks to all those who are doing it, though!

You don't need a chart plotter (who does? hee-hee smiley thing) but you do need an export of NMEA data from GPS and depth.

 

[Saguday]

My log widget thingy arrived yesterday (thanks Tim) complete with USB flash stick, instructions and a calibration sheet. It's quite small and doesn't require much in terms of installation and connection (2 NMEA connections and some power). Won't be able to install it until early December though...