Hi Pat,
This function is in the current beta, which will be released within a few weeks. At the moment, you cannot correct for transducer offset.

thanks,
Matt

ok :)

Than i have to wait for the new release.

Greetings

Hi Matt,

is there any way to correct the offset additional?
I have some Tracks were i did front and backtrolling in 1 Track. I thought about splitting the Tracks and correct the offset additional?!


Cheers

Hi Pat,
At the moment that is not possible.
We are considering moving away from using the heading/course in the sonar logs (they can jump around a bit sometimes, which gives undesirable results). Instead we could calculate the course ourselves using the bearing between consecutive track-points. In principle we would then be able to extend x/y offset functionality to GPX/CSV file imports - so you would be able to split your track, save the segments are reimport them with the differing x/y settings.
Maybe in the next release.

cheers,
Matt

Matt wrote:
That would be wise. Many units doesn't show correct heading unless going above a certain speed.

/Martin

Yeah - I think for most cases it would work better. The potential downside is if you are not moving forwards - eg drifting - then applying offsets using the bearing between conesecutive track-points will give the wrong results. I don't think there is a perfect solution, apart from a proper heading sensor (compass), so you need to exercise a bit of discretion and common-sense when deciding to apply an x/y offset to a track. It some cases it is probably better not to.

Matt

Matt in your oppinion: How important is it to correct an offset of Aft: 0.4 / Starboard: 0.5 ?
How does RF deal with double depth in one Coordinate? Does it build the middle?


Cheers

Honest answer Pat? I would say not very. Even if the map ended up shifted by those amounts - and, in the long run, it would make some small difference to the finished map - you'd never be able to get near to that level of accuracy when using it. If we do get multiple depths in one grid cell (which is not actually that likely with a 1m grid, even with a small map), then we tend to prefer the deeper, although any stark anomalies are likely to be removed in the smoothing process.
Given your earlier post about varying transducer position within a single track, and the small offset involved, I wouldn't bother using an offset at all and wouldn't worry about it too much.

Matt

Yes, that's what i was thinking about.
Then i'll still run without correction.

Thanks Matt!

Pat,

the errors you see as standard on your GPS are far more than the errors you want to correct for. Its certainly not worthwhile correcting for such small amounts, nor is it meaningful. With standard sonar the depth you are reading is the shallowest depth within a circle of varying diameter centred under the boat. The actual sounding that is being recorded could be many meters off to one side, ahead or astern, you have no way of knowing.

Trevor

Hi,

i didn't thought that the standard errors are such "big", thanks for this information.

I do know the principle of sounding: in fact of sounder angle and depth the circle below the sounder becomes bigger/smaller and records the shallowest depth. Thats why fish could stay shallower, if it is at the outside of the circle.

What would be a offset that should be corrected? (Just while thinking about a track of front trolling)


Greetings

But this will also depend on the GPS Receiver you are using.

For example, when you are driving forward wit a left side error of 0.5 meters.
Then drive parallel backwards you will get (worst case) 1 Meter difference.

If you then look at the GPS inaccuracy this error will also be added.
That means you can get a little better or worser Result, depending if the error in the GPS was nearer or farer than the real Point :-)

And on the other side of view, if you have a receiver with accuracy less than 1 meter
you will throw this accuracy away while not correcting.

So for all normal GPS Receivers, which are in accuracy between 1 and 3 meters,
specially if your GPS says it is only 2 or 3 meters accurate,
dont mind about correction or not.

But if you have a better Receiver which says less than 1 Meter accuracy, ...don't throw this away by not correcting.

On my old Humminbird i had an External Receiver which gives me often an accuracy about 1 Meter.
Its minimum reachable error was described under 1 Meter.
But i saw only a few times and not for long an error less than 1 Meter.

Now for my Lowrance Unit i have bought some new GPS Chips from uBlox.
They promised error rates less than 1 meters, which are reproducible been tested by some GPS Cracks.
Sometimes they reached about 0.3 Meters accuracy while testing.