r-计算Home Range区域时出现问题

Question

我在R计算动物的家园范围时遇到了很多麻烦。我想一旦我产生了一个主射程（如果我做得正确的话），计算面积会很容易，但没有

我已经粘贴了一些我一直在尝试的代码。我想知道有人有什么见解吗？

# Load package
    library(adehabitat)
#Load file Frodo
    dd <- read.csv(file.choose(), header = T)
# Plot the home range
    xy <- dd[,c("X","Y")]
    id <- dd[,"name"]
    hr<- mcp(xy,id,percent=95)
    plot(hr)
    points(xy[xy$id=="frodo",])
#Great. Home range produced.  Now calculate area
    area <- mcp.area(xy, id,percent = 95),
# Result 2.287789e-09 Ha.  Way to small.  Maybe it doesnt like Lat / Long.  
# Will try and convert coordinates  into M or Km
# Load map project
    library(mapproj)
    x<-mapproject(t$X,t$Y,projection="mercator")
# Its converted it to something but its not M's  or Km's.  
# I'll try and run it anyway
    xy <- x[,c("X","Y")]
# incorrect number of dimensions
# Ill try Project 4
library(proj4)
    xy <- dd[,c("X","Y")]
    tr <- ptransform(xy/180*pi, '+proj=latlong +ellps=sphere',
                 '+proj=merc +ellps=sphere')
    View(tr)
# There seems to be a Z column filled with 0's. 
# It that going to affect anything? 
# Let's look at the data
    plot(tr)
# Looks good, Lets try and create a home range
    xy <- tr[,c("x","y")]
#  'incorrect number of dimensions'

不知道问题出在哪里。不知道我是走在正确的轨道上还是做了完全错误的事情。

Answer 1

为了计算面积，您需要在投影坐标系中的点（长/纬度中的面积只是度数单位）。你使用的投影类型会对结果区域产生很大影响。例如，墨卡托投影使区域偏离赤道——您可能需要查看您所在位置的最佳等面积投影。我将回答你问题的编程部分，一旦你找到了正确的投影，你就可以在中替换它们

require(sp)
require(rgdal)
orig.points <- dd[,c("X","Y")]
# geographic coordinate system of your points
c1 <- CRS("+proj=latlong +ellps=sphere") 
# define as SpatialPoints
p1 <- SpatialPoints(orig.points, proj4string=c1) 
# define projected coordinate system of your choice, I am using the one you 
# defined above, but see:     
# http://www.remotesensing.org/geotiff/proj_list/mercator_1sp.html
# to make sure your definition of the mercator projection is appropriate
c2 <- CRS("+proj=merc ellps=sphere")
p2 <- spTransform(p1, c2) # project points
# convert to Polygon (this automatically computes the area as an attribute)
poly <- Polygon(p2)
poly@area #will print out the area