How to make additions and subtractions with coordinates?

[MrAxwolf]

Hello everyone, 

 

I'd like to resolve some of mystery cache, but a lot of them require to addition or subtract number to the coordinates. I don't know how to proceed. 

 

An example with random numbers : 

N 56 47.000 + 37 + 62

W 084 15.000 - 40 - 39

Would it be :

N 56 47.099

W 084 14.921

 

If my operations are wrong, can someone tell me how to do the operations!

 

~MrAxwolf

Edited April 19, 2018 by MrAxwolf

[+kunarion]

That's what I often see on cache pages.  But it's good to ask the Cache Owner who knows where the decimal point goes, or at least use the included Geochecker (if it's there).  There is no standard for adding whole numbers to coordinates on cache pages.

[+NYPaddleCacher]

1 hour ago, MrAxwolf said:

Hello everyone, 

 

I'd like to resolve some of mystery cache, but a lot of them require to addition or subtract number to the coordinates. I don't know how to proceed. 

 

An example with random numbers : 

N 56 47.000 + 37 + 62

W 084 15.000 - 40 - 39

Would it be :

N 56 47.099

W 084 14.921

 

If my operations are wrong, can someone tell me how to do the operations!

 

~MrAxwolf

That looks correct to me.  Although the CO may have intended something different, typically when a puzzle requires adding or subtracting a number (or numbers) from coordinates the values for those numbers are in "minutes".  Keep in mind that the "minutes" portions will always be less than 60.0 (there are sixty minutes in a degree) so if the number of minutes added or subtracted results in a value greater than 59.999 or less than zero, the degrees value will have to be adjusted as well.  

That's why, for coordinate math I prefer using Decimal Degrees format.   Decimal Degrees is a single decimal value so "simple math" can be used to calculate new values. 

[MrAxwolf]

35 minutes ago, NYPaddleCacher said:

That looks correct to me.  Although the CO may have intended something different, typically when a puzzle requires adding or subtracting a number (or numbers) from coordinates the values for those numbers are in "minutes".  Keep in mind that the "minutes" portions will always be less than 60.0 (there are sixty minutes in a degree) so if the number of minutes added or subtracted results in a value greater than 59.999 or less than zero, the degrees value will have to be adjusted as well.  

That's why, for coordinate math I prefer using Decimal Degrees format.   Decimal Degrees is a single decimal value so "simple math" can be used to calculate new values. 

And how do you calculate the coordinates with decimal degrees? 

[+Viajero Perdido]

You're trying to read a cache owner's mind here.  There are no standards*.  Try something, check out the result in satellite view, and if it looks reasonable, go there and hunt.

(* N56 47.000 is a poor format for coordinate math, because 0.001 to the west isn't the same distance as 0.001 to the north.  Long story.)

[+arisoft]

2 hours ago, MrAxwolf said:

If my operations are wrong, can someone tell me how to do the operations!

There is no "correct" way as long as the calculation is made with unknown units. It is like adding five bananas to three apples. That makes it a mystery.

For example if we add some arbitrary units to the example it will look like this: N 56° 47.000' + 37 meters + 62 meters = N 56° 47.053'

And another example N 56° 47.000' + 37' + 62' = N 56 47.016

Anyway the most propable unit for this addition is milliminutes N 56° 47.000' + 37*1/1000' + 62*1/1000' = N 56 47.099 as you guessed.

 

[+icezebra11]

10 minutes ago, MrAxwolf said:

And how do you calculate the coordinates with decimal degrees? 

It's just a mathematical conversion.  For example N 12 34.567 converted to decimal degrees is N12 + (34.567/60) = N12.57612

[+NYPaddleCacher]

4 minutes ago, MrAxwolf said:

And how do you calculate the coordinates with decimal degrees? 

In your example above (N 56 47.000 + 37 + 62), 37 and 62 are actually .037 minutes  and .062 minutes which gives you N 56 47.099.

If, however your starting coordinate was N 56 59.950 and you added .037 and .062 you would have to adjust the degrees value as well.  If you did the calculation using DD, all of the values would be represented in degrees as a decimal value.  N 56 59.950 is the same as 55.999167 in decimal degrees.   If you add .037 degrees and .062 degrees to it, the math is 55.999167 + .037 + .062 = 56.098167.   

When doing coordinate math near the equator or greenwhich mean line, things can get confusing when using DDM coordinates.  Typically,  DDM coordinates are written using the hemisphere (N, S, E, W) but they (and DD format) can be written without the.  A coordinate north of the equator always has positive degrees and negative below.  Longitude coordinates east of the greenwich mean line are always negative an positive west of the line.  In order to do coordinate match using DDM one has to first convert the hemisphere character to a 1 or -1 as a multiplier (-1 x 0.2345678 is below the equator, 1 x 0.2345678 is north of it)

If one wanted to add an offset for a a latitude just south of the equator adding a couple of degrees (2.0) would make it a positive value without having to parse and convert the hemisphere string.  

[+icezebra11]

14 minutes ago, NYPaddleCacher said:

Longitude coordinates east of the greenwich mean line are always negative an positive west of the line.

Just the opposite, East is positive and West is negative.

[MrAxwolf]

Ok so if I understand, it does have a lot of possibilities to add and subtract numbers from coordinates. So I only need to figure out which manner the cache owner did his operations. 

[+NYPaddleCacher]

2 hours ago, icezebra11 said:

Just the opposite, East is positive and West is negative.

Oops.  That's correct.  Where things can go wonky is when someone (or more likely, an application) removes the hemisphere but assumes that the degree value is positive.  Note that "S 42 76.123" is valid, but removing "S" without changing the degrees to a negative value would refer to a location in the northern hemisphere.