Comparison Screenshots #2 GT22, CV22, LSS1

[LWINCHESTER2]

What can I say. Sometimes when you cook it, you just have to eat it.

[Larry3215]

I didn't get paid the last time I worked for you!!

Good one , Leonard

Or as my dad used to tell me, "The satisfaction of a job well done is worth more than any amount of pay." - when ever he withheld my allowance.....

[vik]

It occurs to me we can at least test the GT transducers to see if they fire at the same time much easier than the Lowrance test Leonard did and the test Rickie is proposing. With the Garmin GT transducers, you can set the DI and SI to different frequencies. Just do the same path with them both set to the same frequency and again with them on different frequencies. That should isolate the DI and SI image data. Just be sure to have the depth range set far enough to see the fade out of the bottom return on DI.

It would be very interesting for understanding the nature of GT DI and SI views forming. In the beginning looking at first picture below I was sure that GT does not add overlays (returns) from side beams to DI view, but looking at the 2-d and third picture I can not explain why bottom coverage is so wide on 800kHz DI view, unless by getting SI beam returns the same way as Lowrance three element does. I would be excellent to check it by turning off DI and then SI beams to see what happens with DI and SI views, but I think it would be enough to cover them with foam-like materials one by one.

[vik]

You may be right that all it is involved to make the CV image better than the GT image, is a matter of tuning the sensitivity to the just right setting. But I think it is on you to be the one to prove it. In shallow enough water I do think it is possible to turn up the sensitivity and get pretty good images. Better? I've not tried. I'm already fishing water 60-90 feet deep and when you're working with returns that are coming from the edges of the side cones I'm doubtful that the sensitivity can be turned up that much. But I readily admit that this whole business has not been my thing. That is to show as much detail as possible on either the side or down. Ordinarily I would have everything turned to 95 or more and bleach out all the detail to try to get a brighter image of suspended fish. In deep water they are quite small and can be difficult to notice, especially at a glance.

But I am not going to discount what you are saying. But saying it is not sufficient for me. I will wait for the proof and readily applaud you if YOU prove it. I didn't get paid the last time I worked for you!!!

Your screen shots were very helpful for my understanding of Lowrance three element transducer working - now I am for 90% percent sure that they are firing at the same time, and I was wrong presuming that the extra overplayed views came to each view by soft (still need to confirm).
Now I am really very interested in two elements CV DI capability - it would be great if they do not miss anything up 90-95 feet under the boat. I only have Hbird units. All I can do is to check my two element Hbird compact transducer at those depths - it is the dippiest place on our new lake, and then compare with CV results. I was not very happy with my transducer at 70-75 ft depth floating above soft bottom at our old lake - I could not make it hot (bright) even setting of 100% sensitivity. I used my two element Helix 5 SI just a couple of times at new lake, and it's DI showed fish dots along with 2D fish arches quite normal, although the dots were not very bright at 25-35ft ( see screen shots below - small fish is 4-10 inch long). I am going to check it at 95ft depth passing above tennis ball size float which is 3 feet above bottom, and will try to see it on both SI sides - this would confirm that the side beams are overlapped. Not sure about this, but CV CHIRP can do this - this is just a second return to two element DI at higher level :) I am happy with my two element unit, but CV CHIRP is going to be much better.

[Larry3215]

I know its out of character for me, but I cant find anything to disagree with in either of those two posts :)

I would just add one detail - who ever does the next series of tests, be sure to set the depth on the DI views deep enough to show the bottom thickness fading out. If you dont do that you cant be sure you are seeing all of the returns that are included within the cone (or view) and the number for the cone angle will be low.

It would also be good to try the same shots with different gain/brightness levels to see if/how the cone angle changes.

You want the screen to look like this:



or this



Not like this:

http://www.bbcboards.net/attachment....3&d=1491176554


or this

[coachallen]

I would like to know the setting on the GT22.

[LWINCHESTER2]

The width of a cone of returns plays an important role in detail. The narrow cone front to back is what allows for a detailed view. The wide part of the cone, left to right contains more ambiguity. We've already seen when analyzing returns of suspended fish that all we know is how far the fish is away from the transducer, not how deep it is. Images of the bottom would best represent the bottom when we are in an area that is absent of any returns coming from the anything in the water column. The side elements are tilted; neither vertical or horizontal. The center of the cone provides the strongest returns. Above and below the center are weaker returns. Also the more distant returns will be weaker. If the software simply combines the two side views to one view without any filtering what ever structure that is on the left side of the boat would be overlaid with whatever is on the right side. The overlapped part directly under the boat might not be blurred as both elements would have essentially receive near identical returns. Over near flat terrain those images could be quite clear and since they are closest to the xd and the blurring from structure farther away would show as under the bottom. There is the complication of displaying weak signals as opposed to strong ones. A unit with a down element would be receiving much stronger returns in the center of the cone and although distortion (crosstalk) would be present and displayed if they ping at the same time, whatever distortion there would be just as minimal as that of the purposely blended xd without a down element. The distances from the xd to the target would be the same. The distortion that would be observable would be from structure farther away and would be displayed as under the bottom.

In my comparison shots the gain was the same throughout. The image from the CV xd was weaker. Vik said that the image would have been just as good, possibly better if I had turned the gain up. I'm willing to concede that if the return had been stronger the image would have been as good but the return was weaker coming from the edges, not center of the cone. Turning up the gain would help compensate for that. In the above post he acknowledged limitations on using the gain to compensate when in water 70-75 ft deep on the HBird xd. That is a significant limitation, especially for me since I spend so much time fishing water 90-120 ft deep.

The GT transducers are strong transducers. For example, the LSS1 on 800 kHz is practically worthless at 100 ft for showing fish returns. The GT transducers on 800 kHz show fish reliably at this depth. So when comparing the performance of blended DI or direct DI, the depth and the strength of returns is a relevant consideration.

I am using the term "blended DI" to mean a DI image displayed when there is not a separate DI element in the transducer and the term "direct DI" to mean there is a separate DI element in the transducer.

[LWINCHESTER2]

I would like to know the setting on the GT22.

First post
http://www.bbcboards.net/showthread.php?t=800873

[vik]

...be sure to set the depth on the DI views deep enough to show the bottom thickness fading out.

Fully agree, but also be sure that this is the lowest bottom thickness fading out, not just the first ghost shadow right under bottom line.

[Larry3215]

Fully agree, but also be sure that this is the lowest bottom thickness fading out, not just the first ghost shadow right under bottom line.

Yes. In theory, the ghost lines should not be a problem as long as the DI and SI are set to different frequencies. With the Garmin units you will also need to be sure you have any Panoptics transducers turned off. I get ghost lines on 455 when my Panoptics PS21 is on at the same time.

[vik]

... be sure to set the depth on the DI views deep enough to show the bottom thickness fading out.

Good news :) I have found a couple of videos with distinct bottom thickness fading out of Garmin Striker 7 SV GT52 - it is definitely seen that there no any signs of SI beams returns presents on it's DI view - just a pure dedicated DI view either at 455 or 800kHz. It's SI and DI beams are pretty wide and it can allow itself not using of all beams firing at the same time and to have wide SI and clear DI views.

[Larry3215]

It would be very interesting for understanding the nature of GT DI and SI views forming. In the beginning looking at first picture below I was sure that GT does not add overlays (returns) from side beams to DI view, but looking at the 2-d and third picture I can not explain why bottom coverage is so wide on 800kHz DI view, unless by getting SI beam returns the same way as Lowrance three element does. I would be excellent to check it by turning off DI and then SI beams to see what happens with DI and SI views, but I think it would be enough to cover them with foam-like materials one by one.

I think at least a portion of whats going on with the extra wide beam angles is what I mentioned before - we have no idea in most of these images how level the bottom or the target is. When the bottom is not level and flat, it throws the beam angle calculations completely off. An irregular bottom can also have a huge effect on what is blended/overlayed or mixed up on the DI and SI views.

Take a look at this example. Im going to pretend - as we always do - that the beam has nice sharp edges and a specific angle when it really does not.

Imagine you are driving your boat along the edge of a drop off. The closest point on the bottom is the top of the drop off = point A. Point A is 40 ft from the transducer and a little ways to the right of the boat. We have a purple bush sitting about 42 ft to the right. The point directly under the boat is actually about 60 ft deep. To the left side of the boat, the bottom drops off to a dsitance of 85 ft from the transducer and then rises again so that the far left edge of the beam is 80 ft from the transducer.

Note these are NOT depths. They are shown on the screen as depth but they are actually distances from the transducer.

Ive drawn in a yellow "beam" that is roughly 60 deg wide. If you do the calculations based on a bottom thickness that goes from 40 ft to 85 ft, you get a beam angle of 124 deg, when in fact it is only 60 deg. Without knowing exactly how much and which direction the bottom slopes, the calculations have no meaning.

Some other interesting things happen when the bottom is irregular.

The purple tree, that is actually sitting on top of the "bottom", is shown as being partly below the "bottom" on the screen. The further to the right is was, the lower below the bottom line it would be drawn on the screen.

The bottom line, at 40 ft, as shown on the screen, isnt really the bottom thats directly under the boat. Its the point closest to the transducer.

The red arrow represents the bottom thats to the right of point A. The blue arrow represents the part of the bottom to the left of point A. The red arrow will always be drawn on top of the blue arrow on the screen. Those two very different portions of the bottom will always be "blended" or stitched or overlayed no matter how many elements are used and no matter how they fire and no matter what the software is doing. The part of the bottom with the green arrow is also drawn on top of the lower portion of the blue arrow bottom. Note also that the green bottom gets compressed on the screen in addition to being "blended" or stitched or overlayed on top of the blue bottom.

Almost all of that is because all targets are drawn on the screen at the same time and in the order of distance from the transducer. Where they end up on the screen may have no relation to how they are sitting on the bottom. Things that are very far apart can - and will - get drawn on top of each other. This last is true even on a dead flat bottom. Everything on the right side of the beam will always get drawn on top of everything on the left side of the beam. Its just how it works.




widebeam.jpg

[Larry3215]

Good news :) I have found a couple of videos with distinct bottom thickness fading out of Garmin Striker 7 SV GT52 - it is definitely seen that there no any signs of SI beams returns presents on it's DI view - just a pure dedicated DI view either at 455 or 800kHz. It's SI and DI beams are pretty wide and it can allow itself not using of all beams firing at the same time and to have wide SI and clear DI views.

Im not following your logic on this. Its pretty clear in that last image that the portion of the DI view where you have it labeled as 455 has a much wider bottom thickness than the 800 view. It looks to me like the 455 is maybe 118 deg and the 800 is maybe 100 deg. You calculated the first two images DI views at 49 deg.

Why the big differences?

Is it differences in the brightness/gain settings or the bottom slope or is there also some overlap from the SI elements firing - or is it some unknown combination of all three?

It seems to me that there are too many unknown variables to make any conclusions based on these shots.


The brightness settings could have been different on each screen and between the SI and DI and bottom angles could have been very different in each one.

[vik]

Again, completely agree with all your explanations :), I only have changed direction of green arrow on your sketch. Also you could see on all 2D views above that the bottom thickness is small which tells that there is almost no slope, and the width of DI beam coverage depends on sensitivity settings only.

I found one more screen shot below which shows that GT52 uses DI beam only for it's DI view - you see there is no upper structure which is seen by right SI beam, and is not brought to DI view.
If GT52 beams are not firing at the same time then the SI beams overlap is big at shallow water - about 40 degree on this screen shot:
http://www.bbcboards.net/showthread....=1#post8495495

Then CV 52 SI beams overlap can be sufficient at deep water up to 90-95ft I think.

[Larry3215]

Good catch on reversing the green arrow, thanks. Note how that can make interpreting a DI image even more confusing :)

On the rest of it, I will have to get back to you later. I still think you are assuming way too much the images.

I will add one quick thing on the missing target that shows up in sideview but not in DI. Note that it is also missing from the 2D screen and that it does not have any shadow. Then remember lwinchester's images of logs on the surface. That target may not be on the bottom at all.

[LWINCHESTER2]

I found one more screen shot below which shows that GT52 uses DI beam only for it's DI view

So are you saying the Garmin alternates the pings on the GT52? We already know that if all three ping and listen at the same time that each of the three views; left, right, and down will contain return data from the other elements.

I found a GT52 image that may be worth looking at. On the left SideVu just after the school are 5 fish. The DownVu shows 7. There are some very very faint returns on the right side with one a little darker almost touching 40. This one seems to me to only show on the right SideVu. The extra 2 on the DownVu are reasonably bright compared to the others. To the right of the image I copied and slightly enlarged these selected fish. For the SideVu cutout I had to rotate it 90 degrees and flip horizontal to give it the same perspective as the down. Does this tell us anything about alternate pings?

When I posted it, it looked pretty good. Not as good as the original. Then it disappeared. I added the attachment. As an attachment I think it will be too small.

Here is the original

https://drive.google.com/open?id=0B1...FJZLVY5eHhhd1U

[Larry3215]

For some reason your image is not showing up for me.

[Larry3215]

I can see an image link when I quote the post, but it wont show up for me no matter what I do?

[LWINCHESTER2]

I can see an image link when I quote the post, but it wont show up for me no matter what I do?

I added it back along with a link to it on my drive.

[Larry3215]

Ok, I can see it now.

The one thing about that screen shot that confirms the Garmin is firing all elements at the same time is that you have very strong, wide, dark, ghost lines in the SI and DI panels. You shouldnt get those unless they were firing together. There is no way for the signal from the DI to interfere with the signal from the SI and cause that dark band in both views if they are firing alternately or on different frequencies.

It would have been interesting if you had increased the depth range on the DI view. Some more of that big school or the dip in the left side bottom might have shown up below the ghost line if you had. It looks like the bottom return is fading out, but that is really just the start of the ghost line.

As far as the individual fish returns, its really hard to generalize much because we have no idea where they were in relation to each other. The SI cones will have their strongest lobes pointed more to the side and weaker areas above and blow that and weakest in the center where they over lap. The DI will be strongest in the center, but it will also have lobes off to the side. You can see what are probably the same targets in the 2D view. Maybe as many as 8?

I would say the odds are good your assessment is pretty close but I dont think we can tell anything about alternate firing from those returns. Next time set the depth a lot lower on the DI and see what happens.

Its going to be at least another week or maybe two before I can get back on the water to do any testing.