I have some general questions about how to go about solving this problem:
I am trying to incorporate FEWSnet's monthly Rainfall Estimate data from 2014-2015 for Southern Africa into an analysis where I am using a combination of survey data that I collected myself (projected in long/lat coords, WGS84 ellipsoid), the FEWSnet data, and some other rasters/SPDF's that already have projections defined (these are not my concern - I have been able to use projectRaster() and spTransform() to coerce these to new coordinate systems as needed).
The FEWSnet data are challenging because according to their documentation (http://earlywarning.usgs.gov/fews/product/120) they are published in an "Albers Equal Area Conic projection that uses the Clarke 1866 spheroid". But, when I download and read the files into R and call crs() on them, I get "CRS Arguments: NA" in return.
Still being a newbie to these things (and being largely self-taught) I'm confused about exactly what information to use to inform how to correctly set the projection of these data. I've tried looking for an EPSG code for AEA projections in Africa, as well as simply searching the internet for a solution, but am coming up empty. Here is the code that I used to import the data:
# Assume that data are downloaded from the above link, and stored in # a directory on the desktop entitled "Map_Layers". Set this as wd. # "Map_Layers", in my case, contains data from various sources including FEWS # and within FEWS subdirectory are further directories for the raster files # representing year, month, and dekadal periods of rainfall data. DecRFE1 <- raster("./FEWS/2014_Dec_dd1_RFE/s14121rf.bil") DecRFE1 # printed output below... # class : RasterLayer # dimensions : 530, 640, 339200 (nrow, ncol, ncell) # resolution : 8000, 8000 (x, y) # extent : -1456000, 3664000, -4224000, 16000 (xmin, xmax, ymin, ymax) # coord. ref. : NA # data source : /Users/HenryHWells92/Desktop/Map_Layers/FEWS/2014_Dec_dd1_RFE/s14121rf.bil # names : s14121rf # values : 0, 255 (min, max) list.files("./Map_Layers/FEWS/2014_Dec_dd1_RFE") #  "s14121rf.bil" "s14121rf.blw" "s14121rf.clr" "s14121rf.hdr"
So, consider this question a general plea for help on several things:
- How to choose the correct CRS given the information in the files themselves and in the documentation on FEWSnet's website.
- What are the uses of each of the four file types that the FEWSnet data downloads give you? (The .bil files are not in a format that I'm familiar with...)
- If the best way forward is to set a custom projection, what information do I need to do so? Is there an EPSG crs I could take advantage of?