Share Electronics fact I just learned on side scanning

Maybe I am in the minority that did not realize this about side scan. Saw it in an article. It took a couple times reading it for me to get it. Lol. Just sharing in case you didn't know this:

Anglers often mistakenly think when they set their side scan area to 40 feet they are scanning out 40 feet to either side. No not really. You'll notice our depth is around 23 feet. On the ranges on either side the bottom starts being drawn at 23 feet. What you are seeing is directly below the boat on the left and on the right. Then from there it starts scanning out. So really it is scanning out to the "side" roughly 17 feet. The depth alters how far "out to the side" it images. Because it has to look down and then out.

Hmmm, I've never heard that.

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Originally Posted by shadboy

Hmmm, I've never heard that.

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I also had never heard it. I was surprised. I saw it in a pro article in Wired2Fish about reading electronics. Maybe it was wrong? Not sure

Maybe Bob and Rickie can shed some light on this for us.

I'm also curious about this. Been using SI for years and never knew this. I always stop the screen, put the curser on the spot and mark it.

Ask rnvinc. What do you think on this rickie?

theysaid

.THE TRANSDUCER IS SHOOTING OUT HUNDREDS OF FEET BUT THE UNIT IS SET AT 40 FEET,MEANING 40 FEET SIDEWAYS IT WILL PICK UP A OBJECT NEAR TOP OF WATER TO WHERE 40 FEET HIT BOTTOM,SORTA LIKE HAVING A STRING THAT IS 40 FEET LONG,STRETCH IT OUT TO THE SIDE AND LET IT GO AND AS IT DROP DOWN KEEPING LINE TIGHT TILL IT HIT BOTTOM,THIS WILL BE THE DISTANT IT SHOWS THE BOTTOM BUT A FLOATING DOCK THAT IS 39 FEET AWAY WOULD SHOW AS ON BOTTOM AT 39 FEET AWAY FROM DUCER, HOPE I DID NOT CONFUSE YOU ALL

BY THE WAY,THIS IS SLANTED FEET AND SO YOU DO NOT ADD 23 AND 17 TO GET YOUR 40 FEET RANGE,THE BOTTOM COVERAGE WOULD BE ABOUT 35 T0 36 FEET BOTTOM COVERAGE

If I understand right the setting on your side distance really just changes how zoomed in your screen is, not how far the beam actually is going. The beam is going to go as far as it can based on power of the unit.


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I am adding my post just so I can follow this. I am still trying to learn my HDS7 side scan.

It is important to realize that the selected SI Range is not the actual amount of bottom coverage to the left and right (horizontal distance) ...

And while the water depth (23' is this scenario) is figured into the equation (of 40' SI range in this scenario) ... The 40' is Slant Range to the edge of the display (as Gene explained using a 40' long string and arcing this string as one end of the string is attached to the xducer) ...

Slant range is figured using the Pythagorean Theorem ...YUK!! Geometry !!!

In the OP example of 23' water depth with a SI Range setting of 40' ...
http://i477.photobucket.com/albums/r...pspf5dromh.png

Slant Range vs Horizontal Range and Calculating Waypoints

Rickie

Thx for the formula. I understand better when given a math formula.

So when I stop the side scan and mark a waypoint, it accurately log its location. I.e. In the above example, it will mark the 32.7 mark when the 40 foot mark is displayed.

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Originally Posted by crp4570

So when I stop the side scan and mark a waypoint, it accurately log its location. I.e. In the above example, it will mark the 32.7 mark when the 40 foot mark is displayed.

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The unit automatically calculates the slant range to any specific pixel you place a waypoint on ...and assigns the calculated waypoint latitude and longitude coordinates as "summed" in that calculation ... (Is "summed"'a word?) ...

So if you place a waypoint at the edge of the display (with 40' SI Range) ... And then calculate the distance difference between that waypoint's assigned longitude and the boat's present assigned longitude = the difference should sum 32.7' ... (as meaning 32.7' horizontal distance to a point on the water's surface directly above that "thing" you placed the waypoint on) ...

Remember a waypoint's coordinates do not take into account water depth (other than using the water depth in its calculation of slant range to any horizontal pixel on the SI image display) ...

See Sonar Quiz #8 here ...
http://www.crappie.com/crappie/side-...onar-quiz-8-a/

Rickie

You guys didn't know you were Mathathletes did you :highfive:Rofl

So if you turn off the contour lines on a hb unit so the beneath the boat view isn't showing will you get a true 40ft range or will it still be the slant measurement?


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So does this mean that Side imaging range show out farther to the sides when used in shallower water as it is not having to look downward as much.

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Originally Posted by deltabound

So if you turn off the contour lines on a hb unit so the beneath the boat view isn't showing will you get a true 40ft range or will it still be the slant measurement?
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Well slant range ...sorta ...

The 40' (using the same 40' SI Range) with the HB "Contour On" setting eliminates the water column from the displayed image ... but the 40' is still slant range from the xducer to the edge of the display ...

So you're still only seeing 32.7' of bottom coverage (horizontal distance) ... the 32.7' is simply "stretched out" to fill the display without the water column ...

I will explain why the engineers designed it this way in a following post (because it's a lengthy explanation) ...

Rickie

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Originally Posted by rnvinc

Well slant range ...sorta ...

The 40' (using the same 40' SI Range) with the HB "Contour On" setting eliminates the water column from the displayed image ... but the 40' is still slant range from the xducer to the edge of the display ...

So you're still only seeing 32.7' of bottom coverage (horizontal distance) ... the 32.7' is simply "stretched out" to fill the display without the water column ...

I will explain why the engineers designed it this way in a following post (because it's a lengthy explanation) ...

Rickie

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The SI image is a very complex engineering feat ...

This is because the underwater world is 3 dimensional ... and the unit display is only 2 dimensional ...

Engineering the vertical SI scroll data was not that difficult ... It was merely stacking the SI ping slice data one horizontal row of pixels onto the previous horizontal row of pixels ...(remember 1 ping slice data = 1 horizontal pixel row if the Chart speed is scrolling at the same rate as the xducer is pinging)..

The challenge was how to display a 3 dimensional bottom detail onto a 2 dimensional display ...

This is where the slant range calculation design was incorporated ... Basically take into account water depth and the SI Range (slant range) to each target echo and plot echo data into the corresponding pixel in that calculation ... (This is what we see in the HB Contour On setting with no water column) ...

Now the real challenge ... How to display a 3 dimensional water column in this same SI image .. and make it discernible ...

The engineers decided to take the vertical pixel(s) where the bottom detail starts on each side and "move" it outward to make room in the 2 dimensional display for the water column ...

So this created another challenge ... What happens to the bottom detail when the edge of the bottom detail is "moved" outward ?? ...The display is still the same size ... So the existing displayed bottom detail has to be manipulated somehow to make room in the display for the water column ...

So the engineers decided to "compress" the existing bottom detail outward to make room for the water column ...

Imagine 2 accordion style doors opening at the center ... The folds (in the accordion doors) nearest the center are compressed more than the folds at the outer edges ...

Likewise in the SI image = the data closest to the water column is compressed more than the data farther away from the water column ...

You can see in the following image how the exact same data gets compressed in the SI image as compared to the "Contour On" SI data ...

http://i477.photobucket.com/albums/r...psozwjn4xg.png

This is why it is important to understand that range to targets in the SI image should be used as no more than estimations of distance to that target ...

Not only is there slant range calculations in the SI image ...there is also horizontal compression calculations in the SI image ..

Trust that your unit will calculate your SI marked Waypoints to get you in the ballpark ...

Then go verify that waypoint with 2d ... Or hang a lure in it and "re-mark" the waypoint ...

Rickie

Wait.... Wut Happened with SI?? Too much math makes head hurt... why I don't trust no fish on no screen until it's in the boat... even then I have my doubts.. ha..

THAT WAS GOOD RICKIE

Rickie believe it or not I gotcha. Thanks for the in depth info. I can find fish and mark them close enough but it's nice to know it all works. Catching them is a whole nother story in the summer anyhow .....


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Boy, I picked an interesting subject to share. Lol

Ah, The slant. Dats why it is hard to mark and return to suspended fish accurately. If the bait fish are close to surface, you gonna be close. If the are deep, not much so. 2D is you best view when returning to marked suspended fish or bait fish. SI is relative to the bottom. When marking, I mark at the base of the object (opposite the shadow). Inches count. Always remember that everything is relative to the transducer. If your transducer is off to one side, the center of the water column is relative to the transducer, not the center of the boat.

Just some stuff to think about while working your Pythagorean calculator.

My head hurts

Thankfully cuz doesn't talk that way in the boat. He just adjusts all my HB units to where I have to re-learn how to operate them. I don't ask how or why they work, just what it takes me make me understand what is on the screen.

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Originally Posted by tncrappiebass

Boy, I picked an interesting subject to share. Lol

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Discussion is good ...

We continually have new members coming along that this info needs to be re-visited from time to time ...

Rickie

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Originally Posted by scrat

So does this mean that Side imaging range show out farther to the sides when used in shallower water as it is not having to look downward as much.

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That's one way to explain it scrat ...
http://i477.photobucket.com/albums/r...ps9rriyyng.png

Rickie

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Originally Posted by mrdux

Thankfully cuz doesn't talk that way in the boat. He just adjusts all my HB units to where I have to re-learn how to operate them. I don't ask how or why they work, just what it takes me make me understand what is on the screen.

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:biggrin

Rickie

My stuff ain't scientific per se. It is just what I lernt from Pat Haas and piddling.

I new Rickie would know.

Well done Rickie :highfive

My pal Rickie has it dialed in for sure.

The more you know...