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Chartplotter resolution setting advice?

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lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Initially Posted - 09/05/2013 : 21:46:51

A few days ago I replaced the old greyscale Garmin 168 GPS/Sounder in Quiet Time with a newer Garmin 440S color unit that had previously been installed in my last C-22, "Magic". When I went to download it and clear it's track log for use in Quiet Time, I discovered that the tracklog had "wrapped", destroying the tracklog of the first two days of my last San Juans trip. This glitch appears to be due to two issues: 1. the unit was left on all night for two nights on the hook to act as an anchor alarm, recording several thousand useless tracklog points as the boat swung on the anchor with tide changes (I know, I should have stopped track log recording as soon as the hook was set for the night, but I forgot). and 2: For the entire time the unit was installed in Magic, the tracklog resolution was apparently set at some very small default. 40% of the track points were less than 1 boat length apart, and 60% were less than 50 feet apart. That's obviously overkill for cruising.
So, my question to the Forum is, for those of you who have GPS's and like to save your cruising tracklogs for posterity, what tracklog resolution do you favor? I am thinking somewhere between 100~150 feet seems adequate.

Larry Charlot
Catalina 25WK/TR Mk. IV #5857 "Quiet Time"
Folsom Lake, CA

"You might get there faster in a powerboat, but in a sailboat, you're already there"

Edited by - on

britinusa
Web Editor

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USA
5404 Posts

Response Posted - 09/06/2013 : 03:33:27

Great question Larry and something I have not considered.

Regarding the anchor alarm: We use a handheld garmin 72cx (?) for overnight anchor alarms, it has saved our butt several times. It's our backup gps so we don't using while underway unless there is an issue with our main gps a garmin 546.

Regarding memory usage: We download our data from the GPS after most trips onto a PC, but rarely delete tracks. On our older Garmin 192C we had years worth of tracks!

I'll ask the admiral to look at this thread as she is the one that plays with the gps/pc interface regularly.

Thanks for bringing this to light!

Paul

Edited by - on

GaryB
Master Marine Consultant

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USA
4304 Posts

Response Posted - 09/06/2013 : 05:06:57

I just checked the setup on my GPSMAP378 and the "Record Mode" is set to Wrap, the "Interval" is set on Resolution, and the "Value" is set at 82 feet. You may want to set the "Interval" to distance instead of resolution when you are at anchor.

Here's what the manual says about the above values:

1.) Record Mode - Wrap records over the oldest tracks when the track log reaches 100%. Fill records a track log until the track log is full (100%).
2.) Interval - Distance records track points after a specified distance is traveled. Time creates track points after a specified time has elapsed.
Resolution records track points based on the resolution. The higher the resolution entered, the more points the unit creates to make the track.
3.) Value - Records a track according to the Interval and Value. Enter a specific distance, time, or resolution.

Another thing to consider, the track log for my unit will record 10,000 points. I can save 15 tracks on my unit and download others to my PC but don't normally. Yours may record more or less. I couldn't find any info about your unit so check the manual.

Edited by - GaryB on 09/06/2013 05:21:06

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 09/06/2013 : 09:07:19

My Garmin 276 is also set to 82 feet. I wonder what that signifies?

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TakeFive
Master Marine Consultant

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2272 Posts

Response Posted - 09/06/2013 : 10:44:22

I have a Garmin Oregon 400c, so my options may be different. I can't check the settings right now - it's at whatever resolution the default is for the Marine profile.

Every month or so I transfer the current.gpx log file to a computer, and clear out the existing current.gpx file, as well as all stored data.

The one time I failed to clear the stored data and allowed the track points to "wrap," I started getting corruption in my current.gpx log file. Even after clearing it, I still get corruption in the file. I'm not sure that allowing it to wrap caused the problem, but the timing is suspicious.

On my device (YMMV), the current.gpx file is created from scratch every time you plug it into the computer via USB. Apparently the device takes the stored data and writes it into a brand new file called current.gpx. So if you clear the current.gpx file but don't delete the stored data, the same current.gpx file (with the corruption) will reappear later.

Right now I can go for a few trips without the current.gpx file getting corrupted, but at a certain point the corruption always happens. So I'm clearing my data a little more often than I used to.

Fortunately, the corruption consists of a few hundred blank characters that are easily edited out of the current.gpx file with a text editor. But it's annoying, and you can't open the current.gpx file in Homeport, Mapsource, OpenCPN, or any other program without correcting the corruption first.

I've called Garmin to try to get help with this problem, and their phone guys are pretty clueless. Their only resolution is for me to send the device back and get a refurbished one for $100. But I don't really want to do that, since the refurbished one may have the same problem - I won't know until months later when the logs "wrap."

So the moral of my story is, based on my experience, don't allow your device to "wrap." Archive the logs to your computer and clear them out frequently.

Edited by - on

GaryB
Master Marine Consultant

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USA
4304 Posts

Response Posted - 09/06/2013 : 12:26:02

Check to see if you have the Fill option under the Record Mode. If you do and you set it to that option the unit will stop recording your track when it gets to 100% instead of wrapping.

Edited by - on

lcharlot
Master Marine Consultant

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Antigua and Barbuda
1301 Posts

Response Posted - 09/08/2013 : 17:47:19

Thanks for all of your suggestions! If I had known someone who owned a Garmin 440S and been able to check theirs out, I would not have purchased mine. I have never liked the way Garmin totally changed the user interface and menu structure on these newer units compared to the previous generation (those model numbers ending in "8", starting with the 168 and ending with the 498). The 440S is fancier in some ways than the older units, like having a color screen, but it has far less User Information display options than my old Garmin 168 did. It's like Garmin decided that pretty screen graphics were more useful (not!) and would sell more product than lots of numerical data, and redesigned the units accordingly. Worst of all on the 440S there's no way to show depth all by itself in really big numbers. When I am sailing in the shallower parts of SF Bay and the Delta, I can see the shorelines and don't really need the horizontal position stuff; I DO need to see IMMEDIATELY if the water is shoaling and I am about to get outside of the channel: the water to either side of the dredged channel in the San Joaquin River might be only two feet deep, and it doesn't look any different on the surface than the 40' deep water in the middle of the channel. So I want that depth display to be BIG and unmistakeable.

I have reset the tracklog resolution to 100' and will try that next time I take the boat out. I just wish that Garmin would add one feature to all of it's units that support an external memory card: On my Garmin 60CX, there is a setting in the SD Card Menu that causes the operating system to automatically append/record the active tracklog as GPX files (one per calendar day) to the SD card in real time. It's a wonderful feature! I never have to worry about losing tracklog data if the active tracklog goes past 10,000 points and wraps. These backups are not affected by the user erasing the active or saved tracklogs, and they can only be lost permanently if the card itself is deliberately erased or formatted, and that is nearly impossible to do "by accident", you have to key OK at least once at "WARNING! ALL DATA WILL BE LOST!" screens.

Like Rick, I have also had one encounter with corrupt tracklog data on this 400S. About 10 minutes of the tracklog on July 13, 2009 (in the San Juans) was completely haywire: the track suddenly started see-sawing hundreds of yards to the left and right, and all of the leg speeds during that 10 minutes were 1398 knots exactly (bet you didn't know a Catalina 22 could go that fast

). I was in completely open water, no obstructions in the sky over the GPS antenna, no other electrical or RF devices emitting interference on the boat or nearby that I was aware of. Whatever it was, it ended as suddenly as it started and the unit went back to recording a normal tracklog for the rest of the cruise.

Edited by - lcharlot on 09/08/2013 17:58:29

awetmore
Master Marine Consultant

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USA
1144 Posts

Response Posted - 09/08/2013 : 18:08:12

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by delliottg
 My Garmin 276 is also set to 82 feet. I wonder what that signifies?
<hr height="1" noshade id="quote"></blockquote id="quote">

25 meters?

Edited by - on

GaryB
Master Marine Consultant

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USA
4304 Posts

Response Posted - 09/08/2013 : 18:11:58

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by lcharlot
 Thanks for all of your suggestions! If I had known someone who owned a Garmin 440S and been able to check theirs out, I would not have purchased mine. I have never liked the way Garmin totally changed the user interface and menu structure on these newer units compared to the previous generation (those model numbers ending in "8", starting with the 168 and ending with the 498). The 440S is fancier in some ways than the older units, like having a color screen, but it has far less User Information display options than my old Garmin 168 did. It's like Garmin decided that pretty screen graphics were more useful (not!) and would sell more product than lots of numerical data, and redesigned the units accordingly. Worst of all on the 440S there's no way to show depth all by itself in really big numbers. When I am sailing in the shallower parts of SF Bay and the Delta, I can see the shorelines and don't really need the horizontal position stuff; I DO need to see IMMEDIATELY if the water is shoaling and I am about to get outside of the channel: the water to either side of the dredged channel in the San Joaquin River might be only two feet deep, and it doesn't look any different on the surface than the 40' deep water in the middle of the channel. So I want that depth display to be BIG and unmistakeable...

<hr height="1" noshade id="quote"></blockquote id="quote">
I understand your frustration with not being able to set the display to big numbers. As I get older the sight gets worse and I hate having to wear my glasses when trying to see the display while sailing.

Check to see if your unit allows you to set a depth alarm. Might be a workaround for not having the big numbers.

Edited by - GaryB on 09/08/2013 18:12:51

britinusa
Web Editor

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USA
5404 Posts

Response Posted - 09/11/2013 : 13:38:17

Regarding the Interface, I agree with Larry. We had the 192C and it had a 'Page' feature where we could setup which page would display when we pressed the Page Button, it would cycle from the end to the beginning, really nice feature. Our new 546 model requires that we have to navigate to home and then move the cursor to get to the bar that leads to the desired page, it can be several clicks which requires that you have to look at the screen.The old interface required us to just press a button x times to get to the page desired without having to look at the screen. I wrote to Garmin about it, no response, which is unusual as we have had really good customer responses from them previously.

And don't bother asking the reps at the Big Marine Stores! Grrrrr.

Paul

Edited by - on

Stu Jackson C34
Admiral

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844 Posts

Response Posted - 09/12/2013 : 11:20:32

Larry, I hear you! Our GPS Map 76Cx is great in that regard. I forget what I have the track log set to, but when I return from trips I always download the tracks, name them and save them. In many cases, like for races and neat cruises, I print them out and stick them in our log book along with a few pictures. I then erase the tracks from the unit, and can always stick them back on from my computer.

I've sailed a LOT in the Delta, and suggest that you may want to consider avoiding using your depth alarm for guidance. Rather, continue to carefully check both fore and aft that you're staying in the channel, by ranging on the day beacons. While we all know the charts are way old as far as depths, i have found they are pretty accurate. The biggest challenge for me has always been to find the deeper water getting into the Moke from the San Joaquin! I frequent Three River Reach, Potato Slough and Lost Slough, so there's plenty of places to bump bottom, but "knock on wood..." You know the saying...:)

Good luck. Oh, RTFM (F stands for Funny - I got banned from one website for a few weeks because some overly-sensitive moderator didn't get it! :)

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