Matt wrote: NICE!
So then i can use my NEO6P Receivers.

Yep - and if you can log the raw data and post process with base station data then you should be able to achieve very good accuracy. In the UK we have a good network of stations with publicly accessible data, and most places around the coast would be within 25km or so of such a station. In *theory* you could (quite easily) get sub-decimeter accuracy using such a set up, and do it very cheaply.

sounds good Matt - accuracy with egnos switched on is already pretty good, but differential will make it super accurate - i still remember the days of selective availability!!. We actually use a dual GPS antenna system (amongst lots of other receivers) to calculate pitch role and heave, along with an MRU (motion reference unit) at work (this in turn is used for PP of echo sounder and acoustic data). What I was thinking about was if there was anyway of using the sensor in an iPhone (not the GPS, but the mini MRU sensor in it) to get PRH info and use the angles in RM to get even more accurate depth readings? Have no idea if there is any way of recording the PRH data in an iPhone, but there are great little apps that show you 360 degree movement (ball in a circle with displayed angles) and stuff like iPhone spirit levels etc. Was just a side thought though....

www.capsicumdreams.com/iphone/gps2ip/

Useful. Can send roll and heave. I can confirm this works briliantly with just Franson GPSGate running on a laptop and anything that reads NMEA . Elegant little app.

T

AnglingCharts wrote:
I assume you mean roll and pitch, not heave? Heave is (unfortunately) very difficult to measure and there isn't really a way to do it reliably with the gyro/accelerometer/compass combo available on phones (RTK GPS or the post-processed equivalent are likely the best way). It's a shame as heave would probably be the most useful of the adjustments, but we are planning to integrate roll (and maybe pitch) support into sidescan mosaic rendering. The main issue I can see with using a phone (instead of a dedicated unit) is that you would have to position it very precisely w.r.t. the transducer and leave it there for the duration of logging. Ultimately it won't matter where the data comes from once we have implemented a way to synchronise separately logged navigational data with sonar log files.

Err yes - I did actually mean roll and pitch.... I had a little play with it today and it seems rather a useful bit of kit. Hopefully, unless the vessel is articulated, the iphone should be experiencing the same roll and pitch as the transducer wherever it is sited. to be able to simply correct for roll in a basic way would be a big bonus. I dont know if youd need to build some latency into this, or make it adjustable - it would probably be good to be able to play around with it a bit. iPhone seems a very simple solution.

T

One BIG drawback with bow mount instead of stern mount is that the bow moves a lot up/down compared to stern mount which makes the bottom a bit shaky. The solution is as mentioned above to use an accelerometer to calculate heave and remove that from the depth measurement.

To get the best possible heave calculation the accelerometer MUST be very close to the transducer.
Mounting the accelerometer a couple of meters away and then try to calculate the heave at the bow by using heave at the accelerometer + sin(pitch angle) * distance to transducer is a bad idea, the errors will get to large.
On all our systems at work we always have the accelerometer (actually an MRU) as close to the transducer as possible.

/hakan