Side image distance measurements

I was watching a fellow on YouTube, who seemed very knowable, give a class on side image distance measurements and how to determine where a brush pile, stump, etc. is from your boat and he demonstrated it by placing his boat in a parking lot and towing a cooler out to the side and behind his trailer. He proceeded to show how the fish finder displayed this objects distance from the transducer. Everything was clear to my understanding until he said that if the object showed 25 ft to the side of the boat and that you were in 10 ft of water then the object is physically only 15 ft to the side of the boat. He said the transducer shoots a beam to the bottom and then to the side and you must deduct the depth from the displayed distance displayed.

This would have to be taken into account if you threw a marker bouy for instance. But, he said if you use the “mark” button on the fish finder it would mark the correct spot.

Is that correct?


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I saw this same video the other day. Very informative and well explained I thought. Yes that is my understanding too about how he said it showed. Down then out for total. Sort of confusing.

https://youtu.be/VwWqwN28pFw

I thought it was combination of the two beams.


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Originally Posted by lugnutzz

I thought it was combination of the two beams.


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Watch that video. Think it will make it more understandable to you. I stayed confused trying to cypher out distance until I watched it. Now I think I understand it much better.

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Originally Posted by Cray

Watch that video. Think it will make it more understandable to you. I stayed confused trying to cypher out distance until I watched it. Now I think I understand it much better.

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Next time I get out in my boat I’m going to move out to at least ten ft of water and find a tree and then scan it as I pass by and compare the screen distance with the actual.


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I rely on SI to show me fish, structure etc. I then turn to DI or 2D sonar to confirm the depth of what I have discovered and marked by further examination. SI is a valuable tool, but with out down sonar or down image technology it's almost rendered useless in my opinion.

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It is really simple to me . Some say they can not know exactly where the fish are on the screen . I just run curser over and mark fish as a way point then go investigate . Works for me . lol the distance set in 1/4 increments also set on 40 ft helps .

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Originally Posted by RustyJig

I was watching a fellow on YouTube, who seemed very knowable, give a class on side image distance measurements and how to determine where a brush pile, stump, etc. is from your boat and he demonstrated it by placing his boat in a parking lot and towing a cooler out to the side and behind his trailer. He proceeded to show how the fish finder displayed this objects distance from the transducer. Everything was clear to my understanding until he said that if the object showed 25 ft to the side of the boat and that you were in 10 ft of water then the object is physically only 15 ft to the side of the boat. He said the transducer shoots a beam to the bottom and then to the side and you must deduct the depth from the displayed distance displayed.

This would have to be taken into account if you threw a marker bouy for instance. But, he said if you use the “mark” button on the fish finder it would mark the correct spot.

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Let’s start by acknowledging that calculating distance to any target in the SI image is not simply “subtract water depth from the SI range to get distance to target”...

It is physically and scientifically impossible for any Sonar beam (sound traveling in water) to travel to point A and then change directions to get to point B (as in the common misconception of measuring from the xducer to the lake bottom and then measuring out from that point) ...

Horizontal Distance to any target in the SI image is a ”slant range CALCULATION using the Pythagorean Theory” ...

Using the OP scenario of 10’ water depth and seeing a target in the SI image 25’ away from the SI image center line ...:
Attachment 362855

Next we will delve into the HB software engineer’s minds to explain why the HB software engineers designed the SI image layout as they did ...

But 1st I will give space for questions ...

Rickie

I looked at the side image screen shot in the YouTube video and notice that the measurement gradient start at the center of the boat. That would explain why you need to subtract the depth from the total measurement to an object since the screen displays the water column to the bottom before the side image appears.

So here is my conundrum, if you have your helix set to scan 50 ft to the side and you are sitting in 40 ft of water then you are really only scanning 10 ft to the side? Or, are you still scanning 50 ft to the side but only displaying the first 10 ft?

I agree that the helix is probably sending out two beams, one down and one to the side or one beam is rotating from down angle to the side.




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Originally Posted by RustyJig

I looked at the side image screen shot in the YouTube video and notice that the measurement gradient start at the center of the boat. That would explain why you need to subtract the depth from the total measurement to an object since the screen displays the water column to the bottom before the side image appears.

So here is my conundrum, if you have your helix set to scan 50 ft to the side and you are sitting in 40 ft of water then you are really only scanning 10 ft to the side? Or, are you still scanning 50 ft to the side but only displaying the first 10 ft?

I agree that the helix is probably sending out two beams, one down and one to the side or one beam is rotating from down angle to the side

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1. Water depth is not “subtracted” from anything or any measurement - water depth is squared and used in the Pythagorean calculation (a ² + b ² = c ²) to determine horizontal distance ...

2. Correct that you are not seeing but very little of the actual bottom in 40’ of water with SI Range set at 50’ ...

3. There are only 2 side imaging beams, period - one left SI beam pointing 60° left ... and one right SI beam pointing 60° right

4. There are no rotating beams that “change” from pointing one direction to pointing another direction (see #3 above) ...
Every detail in the SI image is rendered from data received from those 2 SI beams noted in #3 above ...

Rickie

We cannot visualize the total displayed SI image as 1 dimensional “plane” under the water ...

This is because the SI image dark water column is more of a geometrical semi-circle (equal to the water depth value) and the bottom detail in the SI image is more of a horizontal plane ...

So it’s important to separate in our minds how we interpret the dark water column in the SI image with how we interpret the bottom detail in the SI image ...

Using this representation of the SI image -
Attachment 362863
Any targets in the magenta color will be “painted” in the SI image dark water column - simply because those targets are closer to the xducer than the actual water depth value (picture in the mind a geometrical semi-circle)

Any targets farther away from the xducer than the value of the water depth will be painted over the bottom detail in the SI image (picture in the mind 1 horizontal plane) ...

Rickie

Once we understand that the dark water column in the SI image must be interpreted separately (in our mind) from how we interpret the bottom detail in the SI image (in our mind) ...

We can see (in the diagram below) that the HB software engineers basically took the left SI image bottom detail and the right SI image bottom detail / and shifted each section of data (left SI and right SI) outward in the displayed SI image to make room in the displayed image for the water column detail ...

Attachment 362864

Rickie

The drawing explains one thing to me I had wrong. I wondered why when I went by trees that were above water and on the edge of my SI range , only show as stumps

I had in my mind the opposite of what in the picture above shows.

This is what I thought I was seeing

Attachment 362865


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Originally Posted by tcounty

The drawing explains one thing to me I had wrong. I wondered why when I went by trees that were above water and on the edge of my SI range , only show as stumps

I had in my mind the opposite of what in the picture above shows.

This is what I thought I was seeing

Attachment 362865

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Unfortunately the HB diagrams on the web leave a little to be desired in fully explaining what is actually in the SI image ...

Rickie

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Originally Posted by rnvinc

Once we understand that the dark water column in the SI image must be interpreted separately (in our mind) from how we interpret the bottom detail in the SI image (in our mind) ...

We can see (in the diagram below) that the HB software engineers basically took the left SI image bottom detail and the right SI image bottom detail / and shifted each section of data (left SI and right SI) outward in the displayed SI image to make room in the displayed image for the water column detail ...

Attachment 362864

Rickie

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So.....if the bottom image ( directly under the boat) is shifted out so that it displays to the rh or lh side of the water column (black area) the side image measurements at the top of the display are off by the depth of the water?

Would the cursor measurement be the same as the top scale?

I noticed from some videos that the side image measurement scale at the top of the display does not change as the boat moves through various depths.






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Now that we understand that the bottom detail is shifted outward left and right in the SI image to make room for the dark water column in the SI image ... we can explain what actually happens to the bottom detail in the SI image ...

Below we see two HB SI images - of the very same bottom detail ...:
Attachment 362887

*The top half is regular SI with the dark water column displayed ...
*The bottom half is SI with HB ‘s “Contour Mode” on - which basically removes the dark water column ...and correctly represents the bottom detail from directly under the boat outward to the user set SI Range selection ...

Notice the individual green marks I have drawn on specific details showing on the lake bottom in both SI images ... and how those specific bottom details are “shifted” (some outward and some inward) when the dark water column is inserted into the SI image ...

The SI Range is not different in the 2 representations - the bottom details at each edge of the screen remain the same ...

But all the other details in the bottom detail are “compressed” to make room in the displayed SI image for the dark water column section ...

This “compression” of the bottom details in the SI image (when the dark water column is displayed) - and the fact that SI Range is “slant range distance - not horizontal distance ... is why the SI Range numbers at the top of the screen should only be used as estimates of distance to targets seen on the bottom detail ...

And the “compression” of the bottom details is also why waypoints marked away from the boat in the SI image cannot be accurate ... and should be re-marked with 2d ...

There is way more going on in the SI image than simple distance from point A to point B ...

Rickie

Quote:

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Originally Posted by rnvinc

Now that we understand that the bottom detail is shifted outward left and right in the SI image to make room for the dark water column in the SI image ... we can explain what actually happens to the bottom detail in the SI image ...

Below we see two HB SI images - of the very same bottom detail ...:
Attachment 362887

*The top half is regular SI with the dark water column displayed ...
*The bottom half is SI with HB ‘s “Contour Mode� on - which basically removes the dark water column ...and correctly represents the bottom detail from directly under the boat outward to the user set SI Range selection ...

Notice the individual green marks I have drawn on specific details showing on the lake bottom and how those specific bottom details are “shifted� outward when the dark water column is inserted into the SI image ...

The SI Range is not different in the 2 representations - the bottom details at each edge of the screen remain the same ...

But all the other details in the bottom detail are “compressed� outward to make room in the displayed SI image for the dark water column section ...

This “compression� of the bottom details in the SI image (when the dark water column is displayed) - and the fact that SI Range is “slant range distance - not horizontal distance ... is why the SI Range numbers at the top of the screen should only be used as estimates of distance to targets seen on the bottom detail ...

And the “compression� of the bottom details is also why waypoints marked away from the boat in the SI image cannot be accurate ... and should be re-marked with 2d ...

Rickie

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Thanks...makes sense now


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The deeper the water the wider your transducers cone.

Quote:

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Originally Posted by RustyJig

I was watching a fellow on YouTube, who seemed very knowable, give a class on side image distance measurements and how to determine where a brush pile, stump, etc. is from your boat and he demonstrated it by placing his boat in a parking lot and towing a cooler out to the side and behind his trailer. He proceeded to show how the fish finder displayed this objects distance from the transducer. Everything was clear to my understanding until he said that if the object showed 25 ft to the side of the boat and that you were in 10 ft of water then the object is physically only 15 ft to the side of the boat. He said the transducer shoots a beam to the bottom and then to the side and you must deduct the depth from the displayed distance displayed.

This would have to be taken into account if you threw a marker bouy for instance. But, he said if you use the “mark” button on the fish finder it would mark the correct spot.

Is that correct?


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come. Agree mind control salesmanship.

Quote:

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Originally Posted by Snubby

I rely on SI to show me fish, structure etc. I then turn to DI or 2D sonar to confirm the depth of what I have discovered and marked by further examination. SI is a valuable tool, but with out down sonar or down image technology it's almost rendered useless in my opinion.

Sent from my SM-G892A using Tapatalk

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I agree 100% the key is a marked fish. Then an immediate seek visit before they swim 50 yes. Remember what Paw said they ain't no fence around them. Constant movements guaranteed when all the electric pulses push down the water colum.

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Originally Posted by eagle 1

It is really simple to me . Some say they can not know exactly where the fish are on the screen . I just run curser over and mark fish as a way point then go investigate . Works for me . lol the distance set in 1/4 increments also set on 40 ft helps .

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My sentiments for sure. Buy fresh miners and keep them lively. Turn the graph off cast miner toward structure.Fish On!!!!!!

Quote:

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Originally Posted by rnvinc

Let’s start by acknowledging that calculating distance to any target in the SI image is not simply “subtract water depth from the SI range to get distance to target�...

It is physically and scientifically impossible for any Sonar beam (sound traveling in water) to travel to point A and then change directions to get to point B (as in the common misconception of measuring from the xducer to the lake bottom and then measuring out from that point) ...

Horizontal Distance to any target in the SI image is a �slant range CALCULATION using the Pythagorean Theory� ...

Using the OP scenario of 10’ water depth and seeing a target in the SI image 25’ away from the SI image center line ...:
Attachment 362855

Next we will delve into the HB software engineer’s minds to explain why the HB software engineers designed the SI image layout as they did ...

But 1st I will give space for questions ...

Rickie

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Yes the boat travels the black centerline of pic on si.

Quote:

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Originally Posted by RustyJig

So.....if the bottom image ( directly under the boat) is shifted out so that it displays to the rh or lh side of the water column (black area) the side image measurements at the top of the display are off by the depth of the water?

Would the cursor measurement be the same as the top scale?

I noticed from some videos that the side image measurement scale at the top of the display does not change as the boat moves through various depths.






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Mark fish as a waypoint, move to it, and fish . :twocents

Quote:

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Originally Posted by sharphook

come. Agree mind control salesmanship.

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Not a sales pitch on my part, I have no stake in the electronics market. It can be done with the same unit, as far as I know all Side Imaging units are capable of 2D and DI. I run mine on split screen the majority of the time.

So we’re better off turning the water column off?


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Quote:

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Originally Posted by RustyJig

I was watching a fellow on YouTube, who seemed very knowable, give a class on side image distance measurements and how to determine where a brush pile, stump, etc. is from your boat and he demonstrated it by placing his boat in a parking lot and towing a cooler out to the side and behind his trailer. He proceeded to show how the fish finder displayed this objects distance from the transducer. Everything was clear to my understanding until he said that if the object showed 25 ft to the side of the boat and that you were in 10 ft of water then the object is physically only 15 ft to the side of the boat. He said the transducer shoots a beam to the bottom and then to the side and you must deduct the depth from the displayed distance displayed.

This would have to be taken into account if you threw a marker bouy for instance. But, he said if you use the “mark” button on the fish finder it would mark the correct spot.

Is that correct?


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---

After reading all of this I have decided that I’m too dumb to use electronics.


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Quote:

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Originally Posted by roachjwr

After reading all of this I have decided that I’m too dumb to use electronics.


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May have to go back to cane pole, Cork and minnow


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Quote:

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Originally Posted by tcounty

So we’re better off turning the water column Offk

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Removing the water column with HB Contour Mode does actually give a better linear representation of the bottom detail without being compressed ...

The disadvantage is losing the details in the water column that one may want to see ...

Rickie

rnvinc , If we are in 30 ft,deep of water
(or less )and set the side image to 40 yds . we would never be off more than a jig pole length(approximately 12 ft ) would we ?

Attachment 363110

Deeper water will exacerbate the difference in the horizontal distance vs slant range distance ...

Rickie

Quote:

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Originally Posted by eagle 1

rnvinc , If we are in 30 ft,deep of water
(or less )and set the side image to 40 yds . we would never be off more than a jig pole length(approximately 12 ft ) would we ?

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Did you mean 40 ft? Instead of yards. If I put my small screen on 120 ft it compresses the pixels to where a stump looks like a dot. LOL


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Attachment 363112

Rickie

Quote:

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Originally Posted by RustyJig

Did you mean 40 ft? Instead of yards. If I put my small screen on 120 ft it compresses the pixels to where a stump looks like a dot. LOL

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I figured the diagram as 40’ SI Range ... (not yds) ...

Rickie