Previous changes to projection format

Question

I have an issue trying to find out the default values from the previously used projection format LCC in R. I can't find any information for that nor an explanation from when they changed it, so I am a bit lost with my old data.

The format used to be:
"+proj=lcc +lat_1=75 +lat_2=50+ellps=WGS84"

The format required now:
"+proj=lcc +lat_1=75 +lat_2=50 +lat_0=?? +lon_0=?? +x_0=? +y_0=? +ellps=WGS84 +datum=WGS84 +units=m +no_defs"

Now a lot more parameters are required which I presume were previously set automatically but I can't figure out how they were defined previously to make my data set work again.

Any ideas?

Answer 1

Running st_crs("+proj=lcc +lat_1=75 +lat_2=50 +ellps=WGS84") gives me:

CONVERSION["unknown",
    METHOD["Lambert Conic Conformal (2SP)",
        ID["EPSG",9802]],
    PARAMETER["Latitude of false origin",0,
        ANGLEUNIT["degree",0.0174532925199433],
        ID["EPSG",8821]],
    PARAMETER["Longitude of false origin",0,
        ANGLEUNIT["degree",0.0174532925199433],
        ID["EPSG",8822]],
    PARAMETER["Latitude of 1st standard parallel",75,
        ANGLEUNIT["degree",0.0174532925199433],
        ID["EPSG",8823]],
    PARAMETER["Latitude of 2nd standard parallel",50,
        ANGLEUNIT["degree",0.0174532925199433],
        ID["EPSG",8824]],
    PARAMETER["Easting at false origin",0,
        LENGTHUNIT["metre",1],
        ID["EPSG",8826]],
    PARAMETER["Northing at false origin",0,
        LENGTHUNIT["metre",1],
        ID["EPSG",8827]]],

Which tells me your four missing parameter defaults are all zero.

So these two should be equivalent:

c1 = "+proj=lcc +lat_1=75 +lat_2=50 +ellps=WGS84"
c2 = "+proj=lcc +lat_1=75 +lat_2=50 +lat_0=0 +lon_0=0 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"

As a quick test lets project some lat-long coords to both and see:

pts = st_as_sf(data.frame(x=runif(10,-180,180), y= runif(10,-90,90)), coords=1:2, crs=4326)
p1 = st_transform(pts, c1)
p2 = st_transform(pts, c2)
st_coordinates(p1) == st_coordinates(p2)

gives:

      X    Y
1  TRUE TRUE
2  TRUE TRUE
3  TRUE TRUE
4  TRUE TRUE
5  TRUE TRUE
6  TRUE TRUE
7  TRUE TRUE
8  TRUE TRUE
9  TRUE TRUE
10 TRUE TRUE

which convinces me.