我正在使用raster在R leaflet映射上绘制大型的NetNetF shinydashboard。当我单击 map 时，会弹出一个窗口，并显示行，列，纬度位置和所单击的栅格点的值。 (请参见下面的可复制代码)
问题是，如果栅格足够大，我正在经历栅格的移动。例如，在这里我单击了一个应该具有值的点，但是结果是所识别的点是上面的点。
我认为这与leaflet使用的栅格是投影的事实有关，而我用来标识点的原始数据是Lat-Lon，因为leaflet将单击的点作为Lat-Lon返回。我无法使用投影文件(depth)，因为它的单位是米，而不是度!
即使我尝试将那些米重新投影到度，我也得到了转变。
这是代码的基本可运行示例:
#Libraries
library(leaflet)
library(raster)
library(shinydashboard)
library(shiny)
#Input data
download.file("https://www.dropbox.com/s/y9ekjod2pt09rvv/test.nc?dl=0", destfile="test.nc")
inputFile = "test.nc"
inputVarName = "Depth"
lldepth <- raster(inputFile, varname=inputVarName)
lldepth[Which(lldepth<=0, cells=T)] <- NA #Set all cells <=0 to NA
ext <- extent(lldepth)
resol <- res(lldepth)
projection(lldepth) <- "+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0"
#Project for leaflet
depth <- projectRasterForLeaflet(lldepth)
#Prepare UI
sbwidth=200
sidebar <- dashboardSidebar(width=sbwidth)
body <- dashboardBody(
box( #https://stackoverflow.com/questions/31278938/how-can-i-make-my-shiny-leafletoutput-have-height-100-while-inside-a-navbarpa
div(class="outer",width = NULL, solidHeader = TRUE, tags$style(type = "text/css", paste0(".outer {position: fixed; top: 50px; left: ", sbwidth, "px; right: 0; bottom: 0px; overflow: hidden; padding: 0}")),
leafletOutput("map", width = "100%", height = "100%")
)
)
)
ui <- dashboardPage(
dashboardHeader(title = "A title"),
sidebar,
body
)
#
#Server instance
server <- function(input, output, session) {
output$map <- renderLeaflet({#Set extent
leaflet() %>%
fitBounds(ext[1], ext[3], ext[2], ext[4])
})
observe({#Observer to show Popups on click
click <- input$map_click
if (!is.null(click)) {
showpos(x=click$lng, y=click$lat)
}
})
showpos <- function(x=NULL, y=NULL) {#Show popup on clicks
#Translate Lat-Lon to cell number using the unprojected raster
#This is because the projected raster is not in degrees, we cannot use it!
cell <- cellFromXY(lldepth, c(x, y))
if (!is.na(cell)) {#If the click is inside the raster...
xy <- xyFromCell(lldepth, cell) #Get the center of the cell
x <- xy[1]
y <- xy[2]
#Get row and column, to print later
rc <- rowColFromCell(lldepth, cell)
#Get value of the given cell
val = depth[cell]
content <- paste0("X=",rc[2],
"; Y=",rc[1],
"; Lon=", round(x, 5),
"; Lat=", round(y, 5),
"; Depth=", round(val, 1), " m")
proxy <- leafletProxy("map")
#add Popup
proxy %>% clearPopups() %>% addPopups(x, y, popup = content)
#add rectangles for testing
proxy %>% clearShapes() %>% addRectangles(x-resol[1]/2, y-resol[2]/2, x+resol[1]/2, y+resol[2]/2)
}
}
#Plot the raster
leafletProxy("map") %>%
addRasterImage(depth, opacity=0.8, project=FALSE, group="Example", layerId="Example", colors=colorNumeric(terrain.colors(10), values(depth), na.color = "black"))
}
print(shinyApp(ui, server))
如果栅格很大，如何正确识别点？
编辑:
我还想提供一些指向(可能)相关文档或问题的附加链接:
最佳答案
我发现我可以重新投影input$map_click给出的X-Y(lon-lat)位置。
在这种情况下，我假设输入投影为Lon-Lat，但我认为不一定必须如此。它只需要有Lat-Lon单位。
#Set projections
inputProj <- "+proj=longlat +datum=WGS84 +ellps=WGS84 +towgs84=0,0,0"
leafletProj <- "+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378137 +b=6378137 +towgs84=0,0,0,0,0,0,0 +units=m +nadgrids=@null +wktext +no_defs"
#Note that for some reason "+nadgrids=@null +wktext" is very important
#as hinted to by other questions and answers linked in my question.
xy <- SpatialPoints(data.frame(x,y))
proj4string(xy) <- inputProj
xy <- as.data.frame(spTransform(xy, leafletProj))
#Get the cell number from the newly transformed metric X and Y.
cell <- cellFromXY(depth, c(xy$x, xy$y))
#At this point, you can also retrace back the center of the cell in
#leaflet coordinates, starting from the cell number!
xy <- SpatialPoints(xyFromCell(depth, cell))
proj4string(xy) <- leafletProj
xy <- as.data.frame(spTransform(xy, inputProj))
#Here XY will again be in lat-lon, if you projection says so,
#indicating the center of the clicked cell
关于r - 在R中标识单击传单中的栅格的位置，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/37523323/