Equivalent of rgdal::make_EPSG()

[Robinlovelace]

Following discussion here we were looking to a way of getting some kind of description of available CRSs and according to @Nowosad this is not possible in sf:

head(rgdal::make_EPSG(), 3)
#>   code     note
#> 1 3819 # HD1909
#> 2 3821  # TWD67
#> 3 3824  # TWD97
#>                                                                                            prj4
#> 1 +proj=longlat +ellps=bessel +towgs84=595.48,121.69,515.35,4.115,-2.9383,0.853,-3.408 +no_defs
#> 2                                                         +proj=longlat +ellps=aust_SA +no_defs
#> 3                                    +proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs

I was tempted to put this in #210 but thought it would be more useful as a separate issue and in case it's already implemented in a way we don't know about.

Thanks.

[edzer]

What you can do is

> st_crs(3819)
Coordinate Reference System:
  EPSG: 3819 
  proj4string: "+proj=longlat +ellps=bessel +towgs84=595.48,121.69,515.35,4.115,-2.9383,0.853,-3.408 +no_defs"
> st_crs(3821)
Coordinate Reference System:
  EPSG: 3821 
  proj4string: "+proj=longlat +ellps=aust_SA +no_defs"
> st_crs(3824)
Coordinate Reference System:
  EPSG: 3824 
  proj4string: "+proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs"

but you don't have access to the set of valid EPSG codes, indeed.

[Robinlovelace]

Is that intended? I can see potential benefits of being able search CRSs by name, e.g. for a user who knows about OSGB but does not know that its EPSG code is 27700.

[Nowosad]

I think that users would find a new function useful. I just used google and searched for "make_EPSG()" - there are many examples of functions and tutorials using this function.

[Robinlovelace]

Reproducible use case (similar searches have been useful for me in the past):

e <- rgdal::make_EPSG()
e[grepl("OSGB", e$note), ]
#>       code                                             note
#> 206   4277                                      # OSGB 1936
#> 207   4278                                         # OSGB70
#> 4003 27700              # OSGB 1936 / British National Grid
#> 5060  7405 # OSGB 1936 / British National Grid + ODN height
#>                                                                                                                    prj4
#> 206                                                                                +proj=longlat +datum=OSGB36 +no_defs
#> 207                                                                                  +proj=longlat +ellps=airy +no_defs
#> 4003           +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +datum=OSGB36 +units=m +no_defs
#> 5060 +proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +datum=OSGB36 +units=m +vunits=m +no_defs

[edzer]

Could one of you explain to me what exactly is wrong with rgdal::make_EPSG?

[Robinlovelace]

Nothing, just another dependency to do a common query possible in the sp world.