Sonar quiz #8

Below are 3 screenshots of the very same brushpile...(I froze the screen scroll and captured all 3 screenshots 1 after the other)..

Each screenshot shows the cursor position in a different spot on the display...

Which cursor position would make the most accurate waypoint in relation to the actual brush pile...??

And explain why...
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Screenshot 1...:

Attachment 272534

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Screenshot 2...:

Attachment 272535

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Screenshot 3...:

Attachment 272536

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Rickie

I'm gonna say #2 because its the highest thickest part of the pile

I am going to say #1 because it seems to work for me. I think ! Looking forward to the real answer with an explanation. Always up to learn something new!!

All of the above

My reason is, because that is where the brush pile actually is on the lakebed. I find it interesting to mark three places when I find something new. I mark one in SI and normally one or two on the DI screen. It is amazing to see how far apart they can be, on the map!

#1...:hesaid

Quote:

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Originally Posted by kosmo

All of the above

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I'm with you, Koz .... seems like the cursor is in exactly the same position (vertically, in relation to the screen), just in three different parts of the water column ... which the GPS isn't reading, anyway, as it's reading where the antenna is. Shouldn't matter where the cursor is (water column depth) for a 2d screen ... since the "brushpile" showing on the screen is locked onto by the GPS antenna, and all three cursor positions are in exact vertical alignment ... so it would seem like the GPS coordinates would be exactly the same. :twocents

... cp :kewl

Someone try it for yourself...and then come back here with your results...

And then we will discuss why this result happens like this...

Rickie

Guessing no.1
Bottom of pile is best as top may be leaning, for instance , a tree,

I think I will guess #1 since they all show different distances from the transducer I'm guessing the bottom of the pile would be closest to the pile; but then I might be wrong and it might be the mark at the top of the water column. I'm interested in the answer and I hope you really know the answer and aren't just making it up.

All three cursor positions are meant to be in a straight vertical line from one another on the 2d image...

The results should be the same on any brand....

Someone test it and come back with your results..

Freeze your screen scroll...mark the bottom of the lake....mark straight up in the 2d image somewhere in midwatercolumn...then mark straight up in the 2d image at the surface....

Check the coordinates of the 3 positions...

Then...We will discuss reasons why...

Rickie

The top one is closer to the satellites!
WINNER!

If it wer SI, I would guess #1, because of the whole slant range thing......The waypoint is more accurate when it is at the bottom contact.

In the case of 2D I woud guess #2 because the 2D cone is more narrow at the shallow point of contact on the brushpile.

Change my vote to what bobb said

Surely someone has been fishing so they can try this...:dono

If anyone has a recording handy...just replay it on the unit and make this same test...

Freeze the screen scroll ...and mark the 3 cursor positions...

(It's even the same result in Humviewer on the 2d image)...

Rickie

So this quiz has no answer?

I am no expert on sonar but I do know enough about GPS to know that the signal will not penetrate water. GPS positioning of targets from a sonar unit are the results of sofisticated software corrections and are subject to the accuracy of cursor placement. I would think that closest to the bottom of the targeted return would be the most accurate. It would still be the least accurate to mark from 2D that SI because of the beam and signal configuration.

:hesaid

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Originally Posted by GroutScout

So this quiz has no answer?

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Yes Grout...there is an answer...I had hoped someone would actually test this on their own unit...

The sonar quizzes I offer intend to spark discussion...not just a simple answer and move on to the next quiz...
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Well I guess no one has actually tried this yet...

The 3 cursor positions will have the exact same coordinates...(as long as the 3 cursor positions are in a direct vertical line)...

GPS is the calculations of "longitude", "latitude", and "altitude"...

Chartplotting "Combo" units (units that have sonar and chartplotting)...do not use the "altitude" part of the scenario ....

I guess sonar companies figure if you get the longitude and latitude correct...the structure you marked should be directly under you...

So, it doesn't matter where in the water column you mark a waypoint on the 2d image....as long as yor intended waypoint mark is in direct vertical alignment with the target you are intending to mark...

Rickie

I suppose that a Barometric altimeter,should be considered?

That's interesting. I still have a hard time coming back but my units are only 5xx units so I don't have the high end antennas like some of the bigger ones.

Good quiz

Very nice Rickie, and I did learn something! Will have to try it tomorrow. I only get to fish on the weekends and the finders are at the lake. I will follow up with my experiment, seems I might not have to be as picky as I have been about placement.

I enjoy the Quiz posts, keep it up!

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Originally Posted by Redge

Very nice Rickie, and I did learn something! Will have to try it tomorrow. I only get to fish on the weekends and the finders are at the lake. I will follow up with my experiment, seems I might not have to be as picky as I have been about placement.

I enjoy the Quiz posts, keep it up!

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Please do post what happens, I'm quite curious if it makes a difference.

You still may not get the EXACT same gps coords if you go back and forth over the structure as the structure could be a few feet wide. If you go back and forth over the structure you may mark a few feet over from your last mark but it looks the same from DI. I have been on structure that was over 20 ft long and had three separate coords marked on it and it looked almost the same each time.

I win!

Quote:

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Originally Posted by brettw

Guessing no.1
Bottom of pile is best as top may be leaning, for instance , a tree,

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Number one is the most accurate, therefore should be used. However, the difference in distance is because the tree, or brush is leaning away from the boat at the same angle as the curser was generated, and the operator should be able to fish the object from any of the marks, but the number one and two would be more accurate.

jerryT, (the new egg in the nest)

Quote:

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Originally Posted by jerryT

Number one is the most accurate, therefore should be used. However, the difference in distance is because the tree, or brush is leaning away from the boat at the same angle as the curser was generated, and the operator should be able to fish the object from any of the marks, but the number one and two would be more accurate.

jerryT, (the new egg in the nest)

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The answer is in post #19 ...
http://www.crappie.com/crappie/side-...ml#post2686994

All 3 cursor positions (when marked in a direct vertical pixel row in the 2d image) will have the exact same latitude and longitude coordinates ...

This is because the unit records and assigns the current GPS coordinates to each "entire vertical pixel row" of echoes as it is "painted" into the 2d image at the very right-most of the screen ...and because that "set" of coordinates is assigned to that vertical pixel row = those assigned coordinates follow that vertical pixel row all the way thru the visible sonar history ...

Freeze the 2d image screen scroll and test ...

Rickie