GPS coordinates units

[+mchaos]

Ok, I searched for a bit, checked the faq and did a quick search on google and didn't find the answer I needed. My question is this....

 

There are a few different kinds of coordinate units you can use and I am not sure which is the most accurate. I am sure the reason that I cannot find an answer is because I just don't know the correct wording for the search.

[+twolpert]

There are a few different kinds of coordinate units you can use and I am not sure which is the most accurate. I am sure the reason that I cannot find an answer is because I just don't know the correct wording for the search.

Makes no difference which you use. The precision is the same. The three formats for lat/lon (decimal degrees, degrees/decimal minutes, degrees/minutes/decimal seconds) have different numbers of decimal places on the smallest unit (degrees, minutes, seconds, respectively). But when you consider the difference in magnitude of the units (60 seconds to the minute, 60 minutes to the degree), they have basically equivalent precision.

 

Accuracy is a different issue. Your recreational or automotive GPSr isn't going to get you any better than maybe +/- 10 feet even with WAAS correction. This error is the limiting factor, not the precision of the lat/lon representation.

 

So pick whichever units suit you and enjoy

[+mchaos]

There are a few different kinds of coordinate units you can use and I am not sure which is the most accurate. I am sure the reason that I cannot find an answer is because I just don't know the correct wording for the search.

Makes no difference which you use. The precision is the same. The three formats for lat/lon (decimal degrees, degrees/decimal minutes, degrees/minutes/decimal seconds) have different numbers of decimal places on the smallest unit (degrees, minutes, seconds, respectively). But when you consider the difference in magnitude of the units (60 seconds to the minute, 60 minutes to the degree), they have basically equivalent precision.

 

Accuracy is a different issue. Your recreational or automotive GPSr isn't going to get you any better than maybe +/- 10 feet even with WAAS correction. This error is the limiting factor, not the precision of the lat/lon representation.

 

So pick whichever units suit you and enjoy

 

So when I am marking a waypoint for where I would like to place a prospective cache, and I take one type of coords, and put it in the cache form, and it converts it to what it shows, it will not be off at all?

[+TotemLake]

There are a few different kinds of coordinate units you can use and I am not sure which is the most accurate. I am sure the reason that I cannot find an answer is because I just don't know the correct wording for the search.

Makes no difference which you use. The precision is the same. The three formats for lat/lon (decimal degrees, degrees/decimal minutes, degrees/minutes/decimal seconds) have different numbers of decimal places on the smallest unit (degrees, minutes, seconds, respectively). But when you consider the difference in magnitude of the units (60 seconds to the minute, 60 minutes to the degree), they have basically equivalent precision.

 

Accuracy is a different issue. Your recreational or automotive GPSr isn't going to get you any better than maybe +/- 10 feet even with WAAS correction. This error is the limiting factor, not the precision of the lat/lon representation.

 

So pick whichever units suit you and enjoy

 

So when I am marking a waypoint for where I would like to place a prospective cache, and I take one type of coords, and put it in the cache form, and it converts it to what it shows, it will not be off at all?

As long as you use the same datum the cache page uses (WGS84), this is a correct statement.

[+mchaos]

Ok, I only ask because on my most recent cache placement, I recorded the waypoint and put it in on the site. I have people saying its 100ft off. I had recently changed the conversion of coords and thought that it may mess with it.

 

I may have been the leaves I guess, but that's the first time I have have gotten such bad coords from my triton.

 

I have to go back and double check them.

[+twolpert]

You'll confuse yourself less if you stick to degrees/decimal minutes which is what gc.com uses. Also, we're all assuming that you're allowing the unit to do the conversion by changing the format. If you're doing it by hand, you're leaving yourself open to simple arithmetic errors. And, as TL points out, be sure to use the WGS84 datum.

 

More likely, though, you just got a high-error fix. When placing a cache, it's always best to do the following. (If you already know this, sorry for the repeat. Maybe somebody else will benefit.)

 

1) Stand still, or better yet, set the unit down for a minute or two BEFORE you mark the waypoint. This allows the unit to "settle", which will result in a more accurate fix.

 

2) If your unit supports averaging, average the waypoint for at least 5 minutes (usually 300 samples or so).

 

3) Test your coordinates by walking a hundred feet or so, then try navigating back to the waypoint. Try this from several different directions. If you can't repeatedly navigate to the WP, cachers certainly won't be able to.

 

4) If it's particularly critical (that ugly micro in the woods), return and repeat on a couple of different days and average the results. This gives you a variety of readings with different satellite constellations, which will hopefully eliminate bad coordinates due to sub-standard constellations.

[+mchaos]

I have never set it down to mark waypoints, just held it still. I will try setting it down.

[AZcachemeister]

Antenna orientation is important here.

If it's a helical antenna, it should be kept upright for best performance. (Magellan meridian, Garmin 60 series)

If it's a patch antenna, it should be horizontal.

 

As far as setting it down goes, the advantage is getting your body (which is mostly water) away from where it can block satellite signals. You could get the same effect by pretending to be the Statue of Liberty.

 

A quick look at the spec sheet for your unit should tell you what kind of antenna it has.