What does the following error mean: TopologyException: found non-nonded intersection between LINESTRING

问题

I'm trying to fortify a shape file that I loaded into R with rgdal, but I get the following error:

"Error: TopologyException: found non-noded intersection between LINESTRING 
        (34.7279 1.59723, 34.7278 1.59729) and LINESTRING 
         (34.7278 1.59723, 34.7278 1.59729) at 34.727793021883102 1.5972887049072426"

I am using a shape file for the continent of Africa from maplibrary.org. It is available from my dropbox here: https://www.dropbox.com/s/etqdw3nky52czv4/Africa%20map.zip

I am using the following code:

library(rgdal)
library(ggplot2)

africa = readOGR("Africa_SHP",    layer = "Africa")
africa.map = fortify(africa, region="COUNTRY")

And I get the error I mentioned before. I take it that R has some problems with the polygon - is there a way around this?

回答1:

As you can see from the comments mdsumner and agstudy were able to answer why this is happening, though agstudy was unable to recreate it with the dataset available. I did find a work-around for this problem.

library(rgdal)
library(rgeos)
library(ggplot2)
#LOADING IN DATA
africa = readOGR("directory", layer="filename")
#FIXING THE NON-NODED INTERSECTS#
africa = gBuffer(africa, width=0, byid=TRUE)
africa.map = fortify(africa, region="ID")

来源：https://stackoverflow.com/questions/13662448/what-does-the-following-error-mean-topologyexception-found-non-nonded-intersec