More external GPS (AS GRP)

[exx1976]

So, I'm about to order an AS GRP. Yes, I had a thread about where to put it, but I still haven't ordered it. LOL

I've been busy, so I haven't gotten out on the lake anyway. This weekend looks good, so the plan is to order one today and get it here and installed for use this weekend.


But - The reason I'm doing this is because my maps looks a bit offset depending on which way I was travelling over what I was mapping, due to the offset between the Helix unit and the transducer location. It was my understanding that the AS GRP was designed to overcome this (or at least minimize it). However, all the sites I've looked at state the AS GRP is "accurate to 2.5 meters". Well, how is that going to help me? My Helix is less than 2.5 meters away from the transducer already, so will I really see an improvement?? I don't want to spend $150 and put more holes in the boat if it's not going to legitmately improve things.


Thanks!

[Wayne P.]

"It was my understanding that the AS GRP was designed to overcome this", no it was not "designed" for that. It does that though.

Adding an external GPS antenna and placing it near the transducer gives you the best accuracy for GPS data that is sonar related.

Some craft with overhead structures that block satellite signals have to use an external GPS antenna located away from the blocking structure to have a functioning GPS.

You won't know in which direction any possible position error is, so at least to minimize the error, adding one will lessen it some. I see 1'-2' EPE with my setups.

[sfw1960]

And an EPE of a few feet will certainly help, I know I can count on my externals heavily too.

[exx1976]

OK, ordered one. Planning to install this week and get on the water this weekend with it.

I'll let you guys know how it does. Hopefully the map turns out better than the last one.

As an aside, does anyone know how to remove autochart pro maps from my ZLC card? Can I just delete the AC folder and then generate new maps with the data I want from autochart pro and update those back into the card? The goal is to remap the lake I did last trip and hopefully remove the anomalies near the shoreline where I was making U turns back and forth across the lake.

Thanks!

[sfw1960]

Don't delete the folder - you can take the files (sort by date) and remove the ones you want (or all if you want to start fresh, but I wouldn't)...

You are aware the more you "run over" a hunk of lake the better the map becomes and will change over "re-sampling" time?

[exx1976]

I figured it would, but how do I ensure that the the newest data with the more accurate GPS location is used to build the map, rather than the old data I used before that cause some bad spots?

[sfw1960]

Because new files overwrite old files.....

[exx1976]

Except that they are different files. Every recording is a different number, so.. ?