使用R和Lattice的XYZ图中高程数据的颜色渐变 [英] Color gradient for elevation data in a XYZ plot with R and Lattice

问题描述

我有一堆XYZ数据，其中X和Y是坐标，而Z应该是高程(LiDAR点).我正在尝试根据Z值绘制带有渐变的点云.

I have a bunch of XYZ data where X and Y are coordinates and Z is supposed to be the elevation (LiDAR points). I am trying to plot this point cloud with a gradient based on the Z value.

这是我到目前为止所拥有的:

Here is what I have so far:

# Read the CSV file with the LiDAR point cloud (which was conveniently converted to CSV)
myData <- read.csv("./52I212_plot10.las.csv")
# We don't need all attributes, let's keep only X, Y and Z.
myData <- subset(myData, select=c(X,Y,Z))
# We want a normalized version of Z (between 0 and 1)
myData$normalZ <- (myData$Z-min(myData$Z))/(max(myData$Z)-min(myData$Z))
str(myData)

为此，我尝试使用以下方式创建情节

With this I try to create the plot with

library(lattice)
ramp <- colorRampPalette(c("lightblue", "red"))
cloud(myData$Z ~ myData$X + myData$Y, xlab="X", ylab="Y", zlab="Z",pch=20,
  col.point=ramp(10)[myData$normalZ*10]) 

我希望Z值具有浅蓝色和红色之间的十种可能的颜色之一.

I expected Z values to have one of ten possible colors between lightblue and red.

当我将plot命令更改为

When I change the plot command to

cloud(myData$Z ~ myData$X + myData$Y, xlab="X", ylab="Y", zlab="Z",pch=20,
  col.point=gray(myData$normalZ))

我得到的东西与我需要的东西更近了:

I get something that is much closer to what I need:

我怀疑我在色带上做错了什么，但无法弄清楚是什么.

I suspect I am doing something wrong on the color ramp, but cannot figure out what.

预先感谢

拉斐尔

编辑

此问题:如何将矢量值与R中的色带中的颜色进行匹配?对我有很大帮助，但是我仍然不明白我做错了什么.这段代码有效:

This question: How to match vector values with colours from a colour ramp in R? helped me a lot, but I still don't understand what I did wrong. This code works:

myData$normalZ <- (myData$Z-min(myData$Z))/(max(myData$Z)-min(myData$Z))
ramp <- colorRamp(c("lightblue", "red"))
cols <- ramp(myData$normalZ)
cloud(myData$Z ~ myData$X + myData$Y, xlab="X", ylab="Y", zlab="Z",pch=20,
      col.point=rgb(cols,maxColorValue = 256))

请指出可以在原始代码上进行哪些更改以使其起作用-我无法弄清楚为什么在第一幅图中颜色看起来是随机的.

Please point what could be changed on the original code to make it work -- I cannot figure out why in the first figure colors appear to be randomish.

谢谢 拉斐尔

推荐答案

没有数据也无法确认，但我认为0会让您失望.您的normalZ在0到1之间，所以10 * normalZ在0到10之间.您将这些非整数传递给[并对其进行了四舍五入. (我必须对此进行查找，但是从?"["开始:"[i]的数值被as.integer强制转换为整数(并因此被截断为零).)

Can't confirm without data, but I think 0's are throwing you off. Your normalZ is between 0 and 1, so 10 * normalZ is between 0 and 10. You're passing these non-integers to [ and they get rounded down. (I had to look this up, but from ?"[": "Numeric values [of i] are coerced to integer as by as.integer (and hence truncated towards zero)".

将0(或小于1的任何内容)作为子集索引使用会弄乱您的颜色矢量的长度，并因此弄乱了它们的匹配方式:

Giving 0 (or anything less than 1) as a subset index messes with your color vector's length and hence how things match up:

ramp(10)[c(0, 0.4, 0.8, 1.2, 1.6)]
# [1] "#ACD8E5" "#ACD8E5"

然后太短的向量将被回收.因此，您的代码可能会与

and then the too-short vector gets recycled. So, your code will probably work with

col.point = ramp(10)[ceiling(myData$normalZ * 10)]

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