Topic: Waypoints from a NAD27 Topo

[Stymie]

Next weekend, I'm going to a lake I don't fish regurlarly.

I have a topo map but the hot spots are in NAD27 coordinates. I also have some friend coordianates that are "standard".

If I enter the NAD27 data per topo in Humminbird PC, copy to the SD card. then set the unit to be in NAD27 before inserting the SD card with the new coordinates, will all these spots be on?

I was thinking of creating two waypoint directories, one in NAD27 and one in "standard" ( think is something 84 ), and changing the setting prior to loading each set.

[RGecy]

Here is a conversion tool.  Not sure how many you have, but switching back and forth would be a pain.  Convert them and just enter manually in to HB PC and transfer to SD card.

http://www.fcc.gov/mb/audio/bickel/DDDMMSS-decimal.html

Robert

[sonar2000]

the most common GPS datum is WGS84.  NADS27 is probably second.  dont know for sure what Google Earth uses.  but if your GPS data is not the same datum the points can be off  enough to miss the relocate spot.  Chuck

[Humminbird_Greg]

Stymie,
I believe that HumminbirdPC references the WGS84 map datum but still waiting for confirmation on this.  So for now I would either convert the waypoints to their WGS84 equivalent using one of the on-line converters like Robert posted or power your unit up while on your boat, set it to the NAD27 (Mean) menu setting (I am assuming that this is the reference the Topo map is using) and manually enter the waypoints one at a time to your Humminbird unit.

[Stymie]

Greg,

You are correct, HPC is WGS84.  I came home today and played around with by entering a few coordinates in HPC, setting the Unit to NAD27 Mean and inserting the SD card.  Moving the cursor to the new waypoints revealed a different setting than what I entered into HPC.  When I changed back to WGS84, and moved the cursor off the waypoint and then back onto it, it showed the entered coordinates.

So, like you said, I started manually entering the coordinates into the units with it set to NAD27 Mean.

I will take a look at the link above tomorrow during lunch.  If it looks like it can be faster, I will finish with that method.  Right now, entering, converting and then entering into HPC, then copying over to SD card seems like a lot of effort.

I did use the HPC for my friend's coordinates.  That's where I hope to catch the fish.  The topo has some old roads, ruins, and dams that I want to locate.  Maybe I can catch some fish there, but if not, should be good practice on the unit.

[Stymie]

Greg,

Some of my waypoints are in H DDD MM SS.S but the unit doesn't do that resolution unless I first convert to H DDD MM.MMM.

Why can't they 1/10 of Seconds?  That should be same resolution as 1/1000 of Minute, right?

That's one more conversion that I was forced to do.  Kind of a pain.

[Humminbird_Greg]

Muskyhunter,
Why wouldn’t you use a GPS Receiver for each unit?  You will already have the GPS Receivers, Y-cable and InterLink module so will not need anything else to make it happen.  The advantage of this is in mounting the GPS Receiver as close to the transducer as possible so you get more accurate waypoints.


It is kind of a pain to have to convert the waypoints Stymie.  I use an Excel spreadsheet and an old version of HumminbirdPC to do large numbers of waypoints just to speed things up.  Takes a while to set the spreadsheet up but it’s a lot quicker than punching in numbers one at a time…

The tenths of a second coordinate format has been asked for but I don’t know if they will do it or not.  If I did my math correctly a tenth of a second of latitude is 10.15 feet while a thousandth of a minute is 6.09 feet.

With the DD.ddddd coordinate format (one-hundred thousandth (1/100,000th or 0.000 01) degree of Latitude) we use now we can show a difference of 3.65 feet.  So I doubt that they will add tenths of a second to the format selection.

[sonar2000]

It took me a bit to convert to the DD.DDDDD   that is decimal degres with a 5 place decimal.  you are right that the accuracy is 3.5 feet.  We have moved all our references to the DD.DDDDD.  It works great.  Unless of courese you want to use UTM.     chuck

[Stymie]

Hey Greg,

The  SS.S helps those of us that have to convert old coordinates given in that format.  Right now, to have any resolution, I have to convert this to either the DD.DDDDD format or the DD MM.MMMMM format.  ( I'm guessing from a shaky memory on the number of decimals for minutes).

Or I can be lazy and round up/down the .S but can be off my spot by 70' or so.

I'd rather the unit to that conversion for me.

It looks like it converts everything to the DD.DDDDD format anyway, so I'm guessing it is a couple of programming scripts that need the calculation adjusted.

This particular lake's topo shows some foundations, bridges, cemetaries, dykes, ponds and what not that I thought would be fun to find whenever the kids needed a break from the fishin.

 I figured instead of landing the boat and going for lunch, we'd pack a lunch and go treasure huntin.  But it was a pain to plug everything in. 

[Humminbird_Greg]

Actually Stymie the unit saves everything in mercator meters and than displays or outputs them in the various coordinate formats.