How many feet is a .001 difference

[+LaPaglia]

yet another newbie question

 

with the format DD MM.mmm:

 

how many feet between

N00 00.001 and 00 00.002 ?

N00 00.010 and 00 00.020 ?

N00 00.100 and 00 00.200 ?

 

Does it change from Lat to Lon or is the difference the same?

 

Thanks

 

Lapaglia

"Muga Muchu" (forget yourself, focus).

[+brdad]

There is a difference! Check out out the 1Mile = ??? thread for detailed info. There are many more but this was a recent one I responded to that had numerous interesting responses.

 

Keep Earth clean, it's not Uranus.

[+Brown Dwarf]

Lots of very precise information on these threads -- but for cache hunting purposes in commonly hunted areas -- like the US -- all you really need is an approximation: 1 minute of angle is about 1 nautical mile is about 6000 feet. Therefore one thousandth of a minute of angle is about 6 feet. Yes, this is an approximation, and yes, the precise answer does depend on whether we're talking about latitude or longitude -- but the other sources of error in the GPS are big enough that moving from an approximation to the precise answer doesn't really buy us anything.

 

Having said that, getting very precise really isn't that hard. Any saltwater sailor has a copy of Bowditch::The American Practical Navigator -- which includes the table Length of a Degree of Latitude and Longitude. [i think NIMA also maintains it on their website.] Easy enough to make up your own crib sheet that tells you that if your latitude is off by x thousandths of a minute, and your longitude is off by y thousandths of a minute, you are z feet from the nominal location of the cache.

 

I've done it, just to see what would happen, but find the six foot approximation mentioned above works just fine in the field.

 

Hope this helps,

BD

[+brdad]

Brown Dwarf, I hear what you're saying and don't want to rehash the subject, did enough of that in the above thread.

 

But if I were to tell you to find a cache at 1º east of my house, which we'll say is at N 45º W 68º, one degree would be just under 49 miles. If you instead used the 6 foot rule, you would be 68 miles from my house. A good deal worse than GPS accuracy.

 

Keep Earth clean, it's not Uranus.

[+Brown Dwarf]

True enough. Guess I leaped to a conclusion here -- that the origin of the question was another question: "how close is 'close'?"

 

Perhaps we can both agree that my approximation is easy and fast in the critical last 0.01 mile. And I'll certainly agree that it's too rough an approximation to use for any distance greater than one or two hundredths of a mile.

 

To recap: 0.01 mile is about 50 feet +/- 25 feet for rounding error; and each 0.001 of a degree is about 6 feet, again +/- 3 feet for rounding.

 

Despite finds that are spot on -- and I've had my share -- this is really about all the accuracy we can coax out of a recreational handheld GPS used under trees.

 

BD

[+Waterboy]

For Latitude, one minute of angle is one nautical mile. For Longitude, one minute of angle is one nautical mile only at the equator. At other locations it varies as the cosine of the Latitude. In other words at 45° Latitude (either north or south) one minute of angle in longitude is equal to 0.7071 nautical mile.

 

A nautical mile is equal to 6,076 ft or 1,852 m.

[+Don&Betty]

Here is a table of "feet per 0.001 minute (miliminute)" that should cover the entire US range of latitudes (and I suppose much of Europe and the southern hemisphere as well). This too I logged somewhere in July 2001. It is based on: feet/mmin = 6.074 * cos(latitude).

 

Find the row which is the degrees of your latitude and the column which is the minutes of your latitude. The entry there is the ft/mmin of longitude at that latitude. The ft/mmin of latitude is always 6.074 ft/mmin, for any longitude.

 

Feet per 0.001 Minute of Longitude at the Degrees and Minutes of Latitude Tabulated

 

____min __0___5___10___15__20__25__30__35___40__45__50__55__

deg

26______5.46 5.46 5.45 5.45 5.44 5.44 5.44 5.43 5.43 5.42 5.42 5.42

27______5.41 5.41 5.40 5.40 5.40 5.39 5.39 5.38 5.38 5.38 5.37 5.37

28______5.36 5.36 5.35 5.35 5.35 5.34 5.34 5.33 5.33 5.33 5.32 5.32

29______5.31 5.31 5.30 5.30 5.30 5.29 5.29 5.28 5.28 5.27 5.27 5.26

 

30______5.26 5.26 5.25 5.25 5.24 5.24 5.23 5.23 5.22 5.22 5.22 5.21

31______5.21 5.20 5.20 5.19 5.19 5.18 5.18 5.17 5.17 5.17 5.16 5.16

32______5.15 5.15 5.14 5.14 5.13 5.13 5.12 5.12 5.11 5.11 5.10 5.10

33______5.09 5.09 5.08 5.08 5.07 5.07 5.07 5.06 5.06 5.05 5.05 5.04

34______5.04 5.03 5.03 5.02 5.02 5.01 5.01 5.00 5.00 4.99 4.99 4.98

 

35______4.98 4.97 4.97 4.96 4.96 4.95 4.94 4.94 4.93 4.93 4.92 4.92

36______4.91 4.91 4.90 4.90 4.89 4.89 4.88 4.88 4.87 4.87 4.86 4.86

37______4.85 4.85 4.84 4.83 4.83 4.82 4.82 4.81 4.81 4.80 4.80 4.79

38______4.79 4.78 4.78 4.77 4.76 4.76 4.75 4.75 4.74 4.74 4.73 4.73

39______4.72 4.71 4.71 4.70 4.70 4.69 4.69 4.68 4.68 4.67 4.66 4.66

 

40______4.65 4.65 4.64 4.64 4.63 4.62 4.62 4.61 4.61 4.60 4.60 4.59

41______4.58 4.58 4.57 4.57 4.56 4.56 4.55 4.54 4.54 4.53 4.53 4.52

42______4.51 4.51 4.50 4.50 4.49 4.48 4.48 4.47 4.47 4.46 4.45 4.45

43______4.44 4.44 4.43 4.42 4.42 4.41 4.41 4.40 4.39 4.39 4.38 4.38

44______4.37 4.36 4.36 4.35 4.34 4.34 4.33 4.33 4.32 4.31 4.31 4.30

 

45______4.29 4.29 4.28 4.28 4.27 4.26 4.26 4.25 4.24 4.24 4.23 4.23

46______4.22 4.21 4.21 4.20 4.19 4.19 4.18 4.17 4.17 4.16 4.16 4.15

47______4.14 4.14 4.13 4.12 4.12 4.11 4.10 4.10 4.09 4.08 4.08 4.07

48______4.06 4.06 4.05 4.04 4.04 4.03 4.02 4.02 4.01 4.00 4.00 3.99

49______3.98 3.98 3.97 3.96 3.96 3.95 3.94 3.94 3.93 3.92 3.92 3.91