I was wondering if it would ever be possible to be able to extract features from the sonar data now that it's viewable in Reefmaster. It would be really cool if we could do bottom point extraction to create even more detailed water beds from this data. I'd imagine this would be a hard interpolation/interpretation to do because of angles and shadows. Still, I'm wondering if it's possible.

I do love what RM does so far but was just curious if this is something that's ever been entertained?

Hi Chez,
Sorry for the late reply - I missed this post.
What sort of features are you talking about? Information from the sidescan? I'm not sure there is a reliable way to do that, even by looking at the sonar viewer, or are you talking about a more fine-grained 2D sonar?

Maybe by taking the mosaicked sonar data and extracting information from that? Is that even possible? It would be cool to build more precise elevation models from the sonar data rather than just have pretty images. I'm not even certain there's any data attached across the images though.

The problem is that sidecan gives us the direct line distance to the feature. From that, we can work out the horizontal distance, if we know the depth, or we could potentially work out the depth, if we knew the horizontal distance. In practice, slant-range correction (essentially, working out the horizontal distance) is done by using the depth under the boat and the straight-line distance to the feature, using simple trigonometry. Of course this can give rise to errors when the feature in question is at a different depth but it's all we have.

Multi-beam sonar, on the other hand, uses an array of narrow cone-angle beams, and this is what is generally used for professional surveying. This can give accurate, high density depths over a broad swath. The only consumer grade multi-beam sonar I have heard of was a Humminbird unit, which has now been discontinued for quite a while..

Agreed. Anything beyond 20 degrees would be big trouble to be able to vouch for accuracy. I've seen bathymetric LiDAR surveys and the corrections they have to apply are almost not worth performing the survey!

I use the Humminbird 899 HD Si which is supposed to have side scan as well as a quad beam sonar. I'll be damned if I can figure out how to get them both working together. They also have a new 360 degree unit which costs a pretty penny but might be worth exploring.

I have ask to Humminbird US to make a black box and a tranducer from 360°which work as a multbean sonar around the boat to do a verticaly one with half of it, they keep that idee!
Last one that they sell was 6 beans and work at 70m deep (desepear when side arrive), I don't remeber but at that time there was 2 softs to make "map" or 3D view from that sounder! I will loook if I find information about it!