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A recent post about the distance of the gps in the head unit and the transducer and the innacuracy that reaults when setting waypoints has got me thinking. Would autochart live contours be off as well if the receiver and the transducer were seperated by any distance? Jsut wondering if I will need a puck if I really want good results.
I would think the inaccuracy of the distance difference (antenna vs depth data) would still be happening ...
Each time the unit receives the return echo data (ping) - the unit assigns the current GPS data sample to that packet of Sonar data ...and plots that Sonar depth data on the Chart view background (plotting on the Chart view background happens with or without map data) ...
So the unit is "plotting" that depth data (mapping contours) relative to where the antenna is ...not where the Sonar depth data actually came from (directly under the xducer) ...
GPS antenna sample data is the Chart view background built into the unit ...
Mapping data (including AutoChart Live) is a transparent overlay layer ...
Rickie
Thanks Rickie. Any reason why Humminbird wouldnt have a head unit transducer offset setting? Seems like that would be an easy update that would take care of the issue. I guess they wouldnt be able to sell the puck at that point whch might answer my question.
I also noticed my build in maps are totally off from my autochart live contour maps. Was mapping the area between two points going from one point to the other to map the channel between them. I was no more that 5 feet from each point when i would turn. When i zoomed out and could see where the land was on my built in map my autochart live contour maps showed my turn well out from the land, close to a full third of the distance between the points. Any idea why they would be so inacurate?
There's actually no telling where HB gets the data for their built in Chart background ...
More than likely from old paper charts ...
That's why these "self mapping" technologies are becoming so popular ...people are realizing that the mapping data they have is just not accurate enough for their liking ...
Rickie
Hmm, interesting.
There's a reason there is a "GPS disclaimer" screen on every bootup of the unit ...Quote:
Originally Posted by Zippy
Rickie
Without a heading sensor GPS, the offset would be meaningless, because when creating a map, the offset for the inaccuracy would be dependent on the direction the boat is traveling....and this would make the mapping algorithm much more complicated.
lol, yupQuote:
There's a reason there is a "GPS disclaimer" screen on every bootup of the unit ...
Thanks Bob, i think i might have to breakdown and get the puck with hs. The cost just keeps adding up.
So.....would you guys recommend getting auto chart live?
It is pretty awesome. I learned to love side and down imaging but for some reason this might be better. It really explains why the fish are where they are. I had a spot on a river that always produced fish in the winter. I found it by accident and kept going back there using reference points on land to line up with it. Once I mapped it I was amazed at what was down there. A shear ledge dropping from 4 feet to over 10 and then a gentle slope to 15 feet. This 15 foot section was about 20 feet wide by 40 feet long. Just a big depression in a 10 foot flat right off a point. Probably the best spot on the river for a crappie to hide from the cold and current. With my new contour map I can get over it without even trying, so cool.
Here is that spot right as i was mapping it
Attachment 226982
ZIPPY,IF IT WAS ME I WOULD NOT WORRY ABOUT THE LITTLE DISTANT FROM DUCER TO UNIT ,I USE MINE ALL THE TIME TO MARK WP AND I CAN GET BACK ON BP THE FIRST TIME NEARLY EVERY TIME,NO NEED FOR A PERFECT WP MARK BECAUSE THE UNIT IS GOING TO BE OFF SOME WITH ANY UNIT.IF U SET ON THE BANK WITH BOAT AND TURN ON UNIT AND TRAIL U WILL SEE YOUR TRAIL MOVE ATLEASE 10 FEET OR MORE.WHEN YOU GO OVER YOUR WP MAKE SURE U ARE GOING STRAIGHT (MOST PEOPLE BIGGEST MISTAKE) AND THE WIDTH OF DUCER WILL PICK IT UP. AFTER U GET GOOD AT GOING TO WP THEN U CAN LEARN HOW TO TURN FROM ONE WP TO ANOTHER WITHOUT GOING STRAIGHT,WHEN USING ARROW TO GET TO WP WHILE TURNING U MUST STOP TURNING BOAT BEFORE ARROW LINES UP WITH TARGET,IT WILL BECOME SECOND NATURE
Sorry, I don't think I was clear enough about the need to have a heading sensor if they were going to offset for mapping purposes.......I was merely trying to point out how complex it would be for them to calculate an offset.Quote:
Originally Posted by Zippy
I didn't mean to say that the unit WILL calculate that offset ..... They have no accommodation for this in their software. The HS GPS is a very nice thing to have, but it won't help you any with gaining mapping accuracy if the transducer and GPS antenna aren't close to each other.
AutoChart Live is only built in to the HELIX 9, 10, 12, and ONIX ...Quote:
Originally Posted by LowePro
AutoChart and AutoChart Pro are Windows based PC software ...which uses Sonar logs to create a map that is then loaded onto a special Zero Lines SD Card and used as a regular LakeMaster map card in the unit ...
If you're not satisfied with the mapping on your home lakes ... Any of the AutoChart products will help you make more accurate maps ...
Rickie
No matter how you offset it or what you buy GPS is only accurate within a couple of feet. It all depends on which satellites you are hitting and strength of signal.
If you're going to do much mapping, you'll absolutely want to get an external GPS receiver placed as close as practical to the transducer.
Here's why:
When mapping, you're basically gathering hundred of datapoints. Each data point includes Lat,Long, and Depth. AutoChart takes allthose data points, and creates a map from those points.
If your gps receiver is gathering Lat, Long coordinatesthat are 8ft away from your transducer, you automatically have at least thatmuch error in your map.
Now, lets say you're surveing an area in a gridpattern. You go over a drop off one way,and come back over it going the other way, and continue. Your GPS coordinates will be 8ft in front ofyour depth from your transducer going each direction. So, if you were to map a drop off with thissetup, your dropoff would look very uneven, when in fact it might be a straightwall without turns.
The closer your gps receiver is to your transducercollecting depths, the better your map will be.