R语言circlize包是怎样的

library(circlize)
library(RColorBrewer)
col<-RColorBrewer::brewer.pal(6,"Paired")
df<-data.frame(chr=sample(c(paste0("chr",1:6)),1000,replace = T),
               x=rnorm(1000),
               y=rnorm(1000))
head(df)
circos.initialize(factors = df$chr,x=df$x)
circos.trackPlotRegion(factors = df$chr,y=df$y,
                       panel.fun = function(x,y){
                         circos.axis()
                       })
for(i in 1:6){
  highlight.sector(sector.index = paste0("chr",i),col=col[i])
  circos.text(CELL_META$xcenter, CELL_META$ycenter,
              labels = paste0("chr",i),sector.index = paste0("chr",i))
}
circos.trackHist(df$chr,df$x,col=col)
circos.link("chr1",0,"chr2",0)
circos.link("chr4",c(-2,0),"chr3",c(-2,2),col="blue")
circos.link("chr4", c(0, 2), "chr6", c(-2, 0), col = "orange")
circos.link("chr5", c(0, 2), "chr1", c(-2, 2), col = "lightgrey")
circos.clear()

这里遇到一个问题是

circos.trackPoints(df$chr,df$x,df$y,pch=16,cex=0.5,col=col)
circos.trackHist(df$chr,df$x,col=col)

为什么circos.trackPoints(df$chr,df$x,df$y,pch=16,cex=0.5,col=col)没有新创建一圈呢？
第二个问题是：
circos.text()函数的两个参数

CELL_META$xcenter

CELL_META$ycenter

是哪里来的呀？如果我想把文本放在每个单元格的中间是固定用这两个参数就可以吗？

另外的参数

• sector.index

• track.index