Understanding Side scan WP placement

[Jethreaux]

Thank you to all for attempting to help me out with this. I find imaging to be really neat and I like to understand how things work.

[contium]

That video isn't completely correct. Side imaging beam isn't 90 degrees. It doesn't go straight down. It goes out at an angle and small objects directly under the boat won't show on side imaging but will on down imaging. All similar demonstrations I've seen using paper printouts don't fold all the way until the sides are touching with a vertical water column but rather as a triangle. This was a point Lowrance was making when Garmin was BS'ing their down imaging by stiching side imaging together because they couldn't run a DI beam.



http://thefishcure.blogspot.com/2015_05_01_archive.html

[DixieChicken]

Still following for sure.

I'm still seeing 358 & 359 20' off to either side of center.
But of course the boat is in roughly 20'~22' of water, and one post says they are *both* directly beneath the boat, 20' away. Say what?

If that holds true, then 355, 356, 357 are literally ZERO feet away from the boat? (As in touching the hull if 358 & 359 are directly beneath, 20' deep.) Seems by the screen that they are directly under the boat, and being as the vessel is moving forward, (using the same distance graph) would not 355 & 356 be closer to 18' (roughly) apart from one another as the boat moved forward, then 357 another 10'-ish feet or so from 356?

Then of course we have 360 that reads 60' out to the left. It can't be 60' deep, and is surely 60' from 355, 356, 357 that are obviously in a straight line.

I get readings like 360 all the time, (which is what I was talking about in my earlier post). Let's say I'm i 15' of water and go to mark a school, lunker, tree, rock etc. and it'll literally say it's 80' to the right. I can mark it on the 2D screen (which is in a window at all times), or on either the TotalScan, or the 3DSS transducer screens (depending on which one I'm reading at the time) and the distances will all be the same. Quite honestly, I've found that TotalScan is pretty darned close to 3DSS as far as the picture I'm seeing most of the time, especially in shallow water like this particular 15' for instance.

It's just strange that marking a spot will show up say 25' forward, and 60'~80' out which would make it literally in a foot of water at best. Or past the edge of the lake on dry land! Which is why I do my SI, DI from deeper water to try and map the bottom. Not to mention I know *NONE* of the transducers will read in 3' of water, been there---done that. (Although I get my shallow water alarm that I have set for 4' each and every time it hits that depth.) Just can't get any readings of the bottom when running that shallow.

Having not used such a powerful tool prior to owning a bass boat (I'd just buy a lake map and stop to read it to try and figure out where I was, and what the bottom was like) I find these tools simply amazing, and am constantly intrigued as to how I can understand AND OPERATE them better.

Even ordered Doctor Sonar's DVD's last week, hoping they'll help my old feeble mind get a better grip on all this fancy tech.

[richhat52]

indiana01 you are correct.

[LittleGazoo]

DownScan has a coverage area:


DOWNSCAN INTERPRETATION:
THIS EXPLANATION IS TO HELP EXPLAIN WHAT YOU SEE WITH DOWN IMAGING, IT IS PERTINENT TO ALL BRAND’S DOWN IMAGING.
DOWN IMAGING HAS A WIDER CONE AND WILL SHOW TARGETS OFF THE SIDE BETTER THAN THE 2D SONAR (TRADITIONAL SONAR 200 KHZ).
NOTICE THE MAN-MADE STRUCTURE PLUS THE ROCKS.
SONAR TELLS US THE DISTANCE TO THE TARGET. THE MAN-MADE STRUCTURE POINTED OUT WITH THE WHITE ARROW IS 8 FEET FROM THE TRANSDUCER. HOW ABOUT THE RED ARROW? IT IS POINTING AT ROCKS AND LONG STRIPS OF SOMETHING MAN-MADE. YOU CAN’T TELL WHICH SIDE IT IS ON SINCE THE LEFT AND RIGHT EDGE OF THE CONE IS COMBINED, SOMETHING 12 FEET FROM THE TRANSDUCER ON THE LEFT WITH BE SUPERIMPOSED ON SOMETHING 12 FEET FROM THE TRANSDUCER ON THE RIGHT SIDE.



IF YOU HAVE SIDE SCAN YOU CAN SEE WHICH SIDE OF THE BOAT A TARGET IS.
NOTICE THE ROCKS ARE OPPOSITE THE MAN-MADE STRUCTURE BUT ON THE DOWNSCAN THEY ARE OVERLAPPED.

================================================== =========
In your StructureScan, waypoint 355 marks the fish which were almost directly under transducer so you waypointed 0ft from transducer. Waypoints 358 & 359 were marked 20ft from the transducer since that just happened to be the depth(and distance from transducer) resulting in 358 & 359 coordinates 20ft horizontally to the side(wrong GPS calculating, see next post).

Here is a not quite to scale picture of DownScan and StructureScan coverage areas:


This information is from Doctor Sonar:
https://doctorsonar.com/blogs/educat...rance-downscan

And another good Lowrance SS and DI video is here:

[LittleGazoo]

And for anyone who is going to ask "How are the GPS coordinates calculated?"

GPS coordinates should be triangulated with the boat transducer at location B and target at location A.


Error will be introduced when the depths at Locations A & C differ.