Format

[stude]

If you have a 121.48922 and change the format my gps60 will read 121.29.353

Will it give the same location?

[+Seay me]

All three of the numbers listed below should be the same geographic location, just in different formats.

 

To put it simply, yes, both of the numbers you listed are the same.

 

DMS 121°29'21.19"

MinDec 121°29.3532

DegDec 121.48922

Edited February 1, 2005 by Seay me

[+Bob Blaylock]

If you have a 121.48922 and change the format my gps60 will  read  121.29.353

Will it give the same location?

  I assume that by “121.29.353”, you mean 121 degrees, 29.353 minutes.  That would be, in decimal degrees, 121.4892167.  Assuming that's a longitude, (too big to be a latitude), and assuming you're at the equator, the difference is about 14 inches.  (The difference is less the farther from the equator).

[stude]

Thanks, That narrows it down a bit.I think it's my compass that is throwing me off.

Edited February 1, 2005 by stude

[+AtoZ]

Since you mentioned your compass what are you trying to do?????

 

cheers

[+strikeforce1]

<Snip> <Snip>The difference is about 14 inches.  (The difference is less the farther from the equator).

WOW,

A whopping 14 inches.

I don't know if I could live with that.

That might put the cache "not under my gps".

 

Yes! I'm making fun at the 14 inches.

Considering we accept distances out past 60 feet as acceptable.

 

The 14 inches, shouldn't be an issue, anywhere in the world.

Happy Caching SF1

[stude]

oh,I been looking up old mine shafts and the ones with the gps readings are differnt sometimes. i joined this group to learn how to use the gps and it's working out good.The last time I turned my compass off because it had me walking in circles.Much better .And the 17' is no big deal with something this large. I'm SE of seattle 30 miles. Thanks

[+briansnat]

oh,I been looking up old mine shafts and the ones with the gps readings are differnt sometimes. i joined this group to learn how to use the gps and it's working out good.The last time I turned my compass off because it had me walking in circles.Much better .And the 17' is no big deal with something this large. I'm SE of seattle 30 miles. Thanks

Are you using the same datum? That can put you pretty far off if you're using different datums.

[stude]

I think I'm ok with the datum but I'll check it.

[noticon75]

Not trying to hijack or anything but why do we use the XX°XX.XXX ' format instead of XX°XX'XX.X"? I prefer degrees minuts seconds over degrees minutes. This may have been discussed before but I didn't know how to word the serch so I wouldn't have to weed thru 1000's of posts. I also thought it fit into this thread well.

[stude]

I can't answer that but if you change the format in my gpsmap60 all my stored locations change also.So it must recalibrate some how.

[+AtoZ]

What you see on the screen is not how the GPS stores values in it's database so when you change units you are just having values displayed in a diffeant format. If you are trying to find mines with a GPS then there is a good chance the listed coordinates are in NAD27 which can be off by 50+ meters from WGS84 coordinates in you neck of the woods.

cheers

[+Poindexter]

The coordinate system used by GPS is called ECEF (earth centered, earth fixed) and is stored internally in this format. This format is converted and displayed to whatever format you select from your setup menu.

 

[+Cardinal Red]

why do we use the XX°XX.XXX ' format instead of XX°XX'XX.X"? I prefer degrees minuts seconds over degrees minutes

 

Use whatever you prefer. You probably won't notice any real difference.

 

The best reason I can think of is how fine is the resolution of your least significant digit in the display. In other words, how far do you have to walk to be able to see a change in the GPS display. Remember I only said DISPLAY. I am sure that internally the math is all done to the same precision.

 

All the numbers I will list below are for LATITUDE only, because they will be the same anywhere on the Earth.

 

DD°MM'SS.S" - the Least Significant Digit represents about 121.5223" - Over a 10' walk.

 

DD°MM.MMM' - the Least Significant Digit represents about 72.9134" - Over a 6' walk.

 

DD.DDDDD° - the Least Significant Digit represents about 43.7480" - Less than a 4' walk.

 

The distance East and West (LONGITUDE) will always be shorter, except on the Equator where it will be equal. On average in the U.S. just multiply the above numbers by about 75%

 

If you want a better idea of distance in LONGITUDE, find a calculator with Trig functions. Enter the Decimal Degrees of the LATITUDE at YOUR location and press the COS (Cosine) button. At 41° Lattitude the ratio between Latitude and Longitude is about 75.47%

 

Why don't I notice those nagging typo's till after it's posted?

Edited February 3, 2005 by Cardinal Red

[+Shoebox]

Here's a free , downloadable program to put on your desktop that converts the formats: http://www.mentorsoftwareinc.com/freebie/FREE1198.HTM

[+Markwell]

DD°MM'SS.S" - the Least Significant Digit represents about 121.5223" - Over a 10' walk.

 

DD°MM.MMM' - the Least Significant Digit represents about 72.9134" - Over a 6' walk.

 

DD.DDDDD° - the Least Significant Digit represents about 43.7480" - Less than a 4' walk.

Also keep in mind that each of those walking distances are less than the EPE of the standard commercial grade GPS. I've never known a GPS to give me the same reading within 10 feet on different days at the same precise location.

 

What you're calling the "Least Significant Digit" is actually just the last displayed digit.

 

So - how significant are those significant digits? UTM coordinate system will get you within 1 meter (3.28 feet). But displaying the coordinates in UTM doesn't make the GPS any more accurate. Just more precise.

 

The drawing is to scale...

Degrees/minutes/seconds to one decimal point at around 10 feet radius of the actual point (shown in the red circle)

Degrees/minutes to three decimal points at around 6 feet radius of the actual point (shown in the purple circle)

Decimal Degrees to five decimal points at under 4 feet radius of the actual point (shown in the light green circle)

UTM at 3.28 feet radius of the actual point (shown in the yellow circle)

 

GREY CIRCLE is the probable error area of the GPS.

 

FWIW, the GPS DOES store even more precise positions internally. I download track logs routinely and they show up to 8 decimal points after the degree, which would be a movement of 0.004 feet - but that doesn't mean my GPS is accurate to that distance.

[+Markwell]

Here's a free , downloadable program to put on your desktop that converts the formats: http://www.mentorsoftwareinc.com/freebie/FREE1198.HTM

And a nicer one here called GeoCalc, written by our own FizzyMagic.

[+Cardinal Red]

Also keep in mind that each of those walking distances are less than the EPE of the standard commercial grade GPS.

 

Nice chart. Somewhere I had referenced displayed digits. I will add to your observation on EPE. That is an estimate of actual accuracy relative to a real world position. Wouldn't you think the accuracy of the distance between two positions only relative to each other would be considerably better than the EPE?

[stude]

Ok,now that I got all that.Finding a pile of rock with a mine in it that has been overgrown and abandon for 40 years shouldn't be that hard.But with the old location description from then and converted to gps it's a challenge.

Thanks Hey,I'm doing better with cashes!