Convert longitude/latitude formats from DMS to D.dec or DM.dec

Test of different packages to convert long/lat data

 Package sp

 Several packages can do the job. First, let use sp package. The orignal data can be in character string or in numbers.

> library("sp")
> essai <- char2dms(from="01d33'01.6\"N", chd="d", chm="'")
> as.numeric(essai)
[1] 1.550444
> essai <- char2dms(from="01°33'01.6\"N", chd="°", chm="'")

Take care, the " character cannot be omitted:

> essai <- char2dms(from="01°33'01.6N", chd="°", chm="'")
> essai
[1] 1d33'N
> as.numeric(essai)
[1] 1.55

Numeric data can be used directly using:

> essai <- new(Class = "DMS", WS=FALSE, deg=1, min=33, sec=1.6, NS=TRUE)
> essai
[1] 1d33'1.6"N
> as.numeric(essai)
[1] 1.550444

And such DMS class object can be obtained from D.dec format using:

> dd2dms(1.550444, NS=TRUE)
[1] 1d33'1.598"N

essai is a S4 object and elements can be accessed using @

> str(essai)
Formal class 'DMS' [package "sp"] with 5 slots
  ..@ WS : logi FALSE
  ..@ deg: int 1
  ..@ min: int 33
  ..@ sec: num 1.6
  ..@ NS : logi TRUE
> essai@deg
[1] 1

 ________________
Package epiR

 Let try now with the epic library. The format data must be in matrix with one, two or 3 columns.

 > library("epiR")
Le chargement a nécessité le package : survival
Package epiR 0.9-77 is loaded
Type help(epi.about) for summary information
> dat <- matrix(c(1, 33, 1.6), nrow=1)
> epi.dms(dat)
         [,1]
[1,] 1.550444
> epi.dms(dat)[1, 1]
[1] 1.550444
> epi.dms(matrix(c(1, 33.02665), nrow=1))[1, 1]
[1] 1.550444

 en conclusion, sp library is more flexible but epiR is the only one to enter data using format DM.dec.

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