I'm looking to produce a map from two separate maps in R. My Maps files are as follows:
ftp://ftp.cpc.ncep.noaa.gov/GIS/us_tempprcpfcst/610prcp_20140822.zip #Map1 ftp://ftp.cpc.ncep.noaa.gov/GIS/us_tempprcpfcst/610prcp_20140812.zip #Map2
These are 6-10 day weather Precip maps from NOAA.
I would like to create a map with the area showing, being only the difference of the two maps. So Map1 - Map2 = Map3. Also, I would like it to show the relative strength of the change for the above or below normal moisture. Which can be seen in the "Prob,N,13,11" & "Cat,C,254" files of the dbf file.
Without success I have tried:
converting to PolySet and then using joinPolys with the Operation="DIFF".
Also:
using readOGR, checking for gIsValid, and then trying to use gDifference.
When I run the second one I get this error:
Error in RGEOSBinTopoFunc(spgeom1, spgeom2, byid, id, drop_not_poly, "rgeos_difference"): TopologyException: no outgoing dirEdge found at -168.86604844949545 63.300706978948405
I am sorry if it seems like such a simple question of taking the difference between two maps but I have been stuck on this question for a number of days now.
