Topic: SI -Range Lines

[RonnieB]

Probably dumb question, but I have lots to learn. When I am looking at SI, with it showing the water column, the range lines start at center line of the water column. To the first 10ft increment range line is including 1/2 of the water column.  So if am I looking at something 100 ft away, is it actually 90? Another way of stating it is: there is 20ft of water column on the map. 10ft on each side of center line. The first 10 ft is actually water column and not horizontal distance. If I took a paper map of it and pinched it together in center, the 10ft line would be actually be "0" or center. 

[rnvinc]

The SI Range lines should be used a general guide and not definite distances to anything ...

Slant Range factors makes this difficult ...

http://forums.sideimagingsoft.com/index.php?topic=946.0
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The SI image shows a left and right water column because there is a left and right SI beam ...

The point where the water column meets the bottom detail is equal to the water depth ...



Any target echo that is closer to the xducer than the water depth will show in the water column of the SI image ...

Any target echo that is farther from the xducer than the water depth will show against the bottom detail ...

*The center line in the SI image is the xducer ...
*The left water column is what the left SI beam "sees" between the xducer and the bottom ...
*The right water column is what the right SI beam "sees" between the xducer and the bottom ...

Rickie

[RonnieB]

to my rescue again rnvinc! Thanks.  I actually had saved that image and that article.    I didn't catch that though.  Slant range is a very deep subject.

[caskey_b]

SI range lines do not factor in depth... so if you are in 10 ft of water, and your first range line reads 10ft, that is actually the ZERO mark, right under the boat...

but as mentioned above... angles play a huge factor in determining suspending fish... however, you can be fairly accurate with distance with bottom objects if you factor in the water column..

I run my SI without range lines... I feel as if they clutter up my screen... I usually fish between 50-75ft ranges so if I want to cast to something, I just quickly guestimate the distance...

[rnvinc]

to my rescue again rnvinc! Thanks.  I actually had saved that image and that article.    I didn't catch that though.  Slant range is a very deep subject.

The difficulty is Slant range estimation is taking into account the compression factor involved in the SI image processing ...

Contour Mode actually gives a better scenario for estimating distances to outbound objects due to the lack of compression of the 1st few feet of bottom detail ...



Notice how the 1st few feet of the bottom detail away from the water column is compressed to allow room for the water column in the SI image ...

Rickie