在R中创建地形图 [英] Create topographic map in R
问题描述
我正在尝试创建一个脚本,该脚本将为给定的一组坐标生成二维地形图或轮廓图.我的目标与
I am trying to create a script that will generate a 2d topographic or contour map for a given set of coordinates. My goal is something similar to what is produced by
轮廓(火山)
,但对于用户设置的任何位置.事实证明,这极具挑战性!我已经尝试过:
but for any location set by the user. This has proved surprisingly challenging! I have tried:
library(elevatr)
library(tidyr)
# Generate a data frame of lat/long coordinates.
ex.df <- data.frame(x=seq(from=-73, to=-71, length.out=10),
y=seq(from=41, to=45, length.out=10))
# Specify projection.
prj_dd <- "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs"
# Use elevatr package to get elevation data for each point.
df.sp <- get_elev_point(ex.df, prj = prj_dd, src = "epqs")
# Convert from spatial to regular data frame, remove extra column.
# Use tidyr to convert to lat x lon table with elevation as fill.
# Sorry for the terrible code, I know this is sloppy.
df <- as.data.frame(df.sp)
df$elev_units <- NULL
df.w <- df %>% spread(y, elevation)
df.w <- as.matrix(df.w)
这将创建一个类似于 volcano
数据集的矩阵,但将其填充为 NA
s,除了带有海拔数据的10个经纬度对. contour
可以处理 NA
,但是 contour(df.w)
的结果只有一条细线.我不确定从这里要去哪里.我是否只需要更多积分?预先感谢您提供的任何帮助-我对R还是很陌生,我认为我付出的努力超过了我对这个项目的了解.
This creates a matrix similar to the volcano
dataset but filled with NA
s except for the 10 lat/lon pairs with elevation data. contour
can handle NA
s, but the result of contour(df.w)
has only a single tiny line on it. I'm not sure where to go from here. Do I simply need more points? Thanks in advance for any help--I'm pretty new to R and I think I've bitten off more than I can chew with this project.
推荐答案
抱歉,响应延迟.我想我需要检查 elevatr
问题!
Sorry for delay in responding. I suppose I need to check SO for elevatr
questions!
我将使用 elevatr :: get_elev_raster()
,它返回一个栅格对象,可以直接使用 raster :: contour()
绘制该对象.
I would use elevatr::get_elev_raster()
, which returns a raster object which can be plotted directly with raster::contour()
.
下面的代码示例以较小的分辨率捕获较小的区域.最终的轮廓看起来不错.
Code example below grabs a smaller area and at a pretty coarse resolution. Resultant contour looks decent though.
library(elevatr)
library(raster)
# Generate a data frame of lat/long coordinates.
ex.df <- data.frame(x=seq(from=-73, to=-72.5, length.out=10),
y=seq(from=41, to=41.5, length.out=10))
# Specify projection.
prj_dd <- "+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs"
# Use elevatr package to get elevation data for each point.
elev <- get_elev_raster(ex.df, prj = prj_dd, z = 10, clip = "bbox")
raster::contour(elev)
如果需要使用 graphic :: contour()
,则需要先使用 raster :: as.matrix(elev)将栅格对象转换为矩阵.
.但这使坐标发生了变化,我还没有花费足够的时间尝试弄清楚那一部分...希望 raster
解决方案对您有用.
If it is a requirement to use graphic::contour()
, you'll need to convert the raster object to a matrix first with raster::as.matrix(elev)
. That flips the coords though and I haven't spent enough time to try and get that part figured out... Hopefully the raster
solution works for you.
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