存在 - 缺少数据集

Question

我试图在R中生成缺席和存在数据集以用于后续模型。我有多个带有位置的csv表和与这些位置匹配的植被栅格。我需要生成一个存在缺失数据集来模拟栖息地选择。我已经完成了脚本：

setwd("~/Masters/Research Project/GIS/GIS_Focal_Raster")    
library(raster)    

## import the raster layer used as the mask                            ##

absent<-raster("Veg_B2.tif")    
mask<-raster(absent)    

present<-read.csv("B2_Lon_Lat.csv")    
present    

## select 500 random points                                            ##
## set seed to assure that the examples will always have the same      ##
## random sample.                                                      ##

library(dismo)    
set.seed(1963)     
bg<-randomPoints(mask,500)     

## set up the plotting area for two maps                               ##
par(mfrow=c(1,2))     
plot(!is.na(mask),legend=FALSE,main="random")     
points(bg,cex=0.5)     

## repeat the sampling, but limit the area of sampling using a spatial ##
## extent                                                              ##

library(raster)     
library(extent)    

r<-raster("Veg_B2.tif")    
e<-extent(r)     

bg2<-randomPoints(mask,50,ext=e)     
plot(!is.na(mask),legend=FALSE)    
plot(e,add=TRUE,col='red')     
points(bg2,cex=0.5)     

## pseudo-absence points                                               ##

library(rgdal)     
present<-read.csv("B2_Lon_Lat.csv")      
coordinates(present)=~lon+lat     

然后我想出了错误

  

坐标（本）=〜经度纬度+   eval中的错误（predvars，data，env）：object＆＃39; lon＆＃39;未找到   有什么建议怎么继续？