rozap / reproject

elixir nif for proj4, inspiration from greenelephantlabs/proj4erl

reproject

Reproject a point. This is just a nif that calls into proj4 and gdal

Setup

You need proj4 and gdal installed on your system. Install it with

sudo apt-get install libproj-dev libgdal1-dev

You may need to build from source. Download proj 4.9.3 here and ./configure && make && make install. On ubuntu 20, you may need to add /usr/local/lib to your library path, like export LD_LIBRARY_PATH=/lib:/usr/lib:/usr/local/lib

Then mix compile should work and mix test should pass.

Usage

Initialize a projection from a proj4 string

iex> {:ok, prj} = Reproject.create("+init=epsg:4326")

Initialize a projection from a PRJ component of a shapefile

{:ok, prj} = Reproject.create_from_prj("""
  GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433],AUTHORITY["EPSG",4326]]
""")

Initialize a projection from a WKT string

{:ok, prj} = Reproject.create_from_wkt("""
  GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.257223563]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.0174532925199433],AUTHORITY["EPSG",4326]]
""")

Transform a point from source projection to dest projection

iex> {:ok, wgs84} = Reproject.create("+init=epsg:4326")
iex> {:ok, crs2180} = Reproject.create("+init=epsg:2180")
iex> Reproject.transform(wgs84, crs2180, {21.049804687501, 52.22900390625})
{:ok, {639951.5695094677, 486751.7840663176}}

Get the expanded projection definition

iex> Reproject.expand(prj)
" +init=epsg:4326 +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0"