Spatial function

[Rafnuss]

Provide three new functions related to spatial ability:

• find_pentad Find the pentad code of GPS coordinate
• find_pentad_coordinate Find the GPS coordinate of pentad code
• find_pentad_within Find the pentad overlapping a given shape

Note that I'm not using any pre-existing pentads (e.g. geojson file) but I'm using the name convention.

The symbole between lat and lon is determined with :

    if (lat < 0 & lon > 0){
      letter <- '_'
    } else if (lat < 0 & lon < 0) {
      letter <- 'a'
    } else if (lat > 0  & lon < 0) {
      letter <- 'b'
    } else if (lat > 0 & lon > 0) {
      letter <- 'c'

I don't know what happen if lon >99 and therefore the functions are not implemented for this yet.

[davidclarance]

Excellent work @Rafnuss !

[Rafnuss]

Thanks! I found several bug with this set of functions. Happy to submit the corrected version if implmented.