在gglot2中将SVG图像用作符号 [英] Use SVG images as symbols in gglot2

问题描述

我想将存储在外部文件(例如SVG)中的矢量图形用作 ggplot2 图中的绘图符号.例如按照grImport插图的示例进行操作(图8)

此示例导入​​自定义shapefile，然后使用 lattice 例如

对其进行绘制

  xyplot(V8〜V7，data = flower，xlab ="Height"，ylab =分开距离"，panel = function(x，y，...){grid.symbols(PSflower，x，y，units ="native"，大小=单位(5，"mm"))}) 

来自 grImport 包的 grid.symbols()，而 PSflower 是由 grImport导入其他位置的Picture对象

代码>.

ggimage 包接近完成此操作，但是它将图像转换为绘图以下的栅格，这是我要避免的事情.

有什么办法可以在 ggplot2 中实现类似的功能吗?

标记

解决方案

这是我想出的解决方案-效果很好.您也可以使用 grImport 做类似的技巧.关键是要确保grob的标准化绘图坐标与ggplot的原始坐标相匹配.

  #Setup图书馆(grImport2)库(ggplot2)图书馆(秤)src.file<-system.file("SVG"，"lwd-rsvg.svg"，package ="grImport2")img<-readPicture(src.file)#现在创建一些数据d<-data.frame(x = 1:5，y = 1:5)#需要指定绘图的xlims和ylims-这可以让我们计算#normalized绘图坐标xlims<-c(0,6)ylims<-c(0,6)#使用symbolGrob创建绘图点sym.grob<-symbolsGrob(img，x = rescale(d $ x，from = xlims)，y = rescale(d $ y，from = ylims)，default.units ="npc"，大小= 0.3)#阴谋ggplot(d，aes(x，y))+geom_point()+注解_自定义(sym.grob)+coord_cartesian(xlim = xlims，ylim = ylims，expand = FALSE)#别忘了这个！ 

I would like to use vector graphics stored in external files (e.g. SVG) as my plotting symbols in a ggplot2 figure. e.g. following this example from the grImport vignette (Fig. 8) https://cran.r-project.org/web/packages/grImport/vignettes/import.pdf

This example imports a custom shapefile and then plots it using lattice e.g.

xyplot(V8 ~ V7, data = flower, xlab = "Height",
               ylab = "Distance Apart",
               panel = function(x, y, ...) {
                                grid.symbols(PSflower, x, y, units = "native",                     
                                             size = unit(5, "mm"))})

with grid.symbols() coming from the grImport package and PSflower being a Picture object imported elsewhere by grImport.

The ggimage package gets close to doing this, but it converts the image to a raster below plotting, which is what I'm trying to avoid.

Is there any way I could implement something similar in ggplot2?

Mark

解决方案

This is the solution that I came up with - seems to work pretty well. You can also do a similar trick with grImport. The key is making sure that the normalised plot coordinates of the grob matches up with the native coordinates of ggplot.

#Setup
library(grImport2)
library(ggplot2)
library(scales)
src.file <- system.file("SVG", "lwd-rsvg.svg", package="grImport2")
img <- readPicture(src.file)

#Now createa some data
d <- data.frame(x=1:5,y=1:5)

#Need to specify xlims and ylims of plot - this lets us calculate the
#normalised plot coordinates
xlims <- c(0,6)
ylims <- c(0,6)

#Create the plot points using symbolsGrob
sym.grob <- symbolsGrob(img,
                        x=rescale(d$x,from=xlims),
                        y=rescale(d$y,from=ylims),
                        default.units="npc",
                        size=0.3)

#Plot
ggplot(d,aes(x,y))+
  geom_point()+
  annotation_custom(sym.grob)+
  coord_cartesian(xlim=xlims,ylim=ylims,expand=FALSE) #Don't forget this!

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