r - spTransform() : "No transformation possible from NA reference system"

Question

我有一个包含 2017 年发生的所有 Stop 和 Frisks 的表格。我得到了它们在长岛坐标中发生位置的坐标，但我想将其转换为纬度和经度坐标，以便我可以在 Leaflet 中绘制它。

我有以下代码片段:

library(sp)
library(dplyr)

fd <- "https://www1.nyc.gov/assets/nypd/downloads/excel/analysis_and_planning/stop-question-frisk/sqf-2017.csv"
stop_and_frisk <- read.csv(fd)

saf <- stop_and_frisk %>% filter(STOP_FRISK_ID < 5 ) # filtering to keep data small
saf_spdf <- saf

coordinates(saf_spdf) <- ~STOP_LOCATION_X + STOP_LOCATION_Y
CRS_obj <- CRS('+proj=lcc +lat_1=41.03333333333333 +lat_2=40.66666666666666 +lat_0=40.16666666666666 +lon_0=-74 +x_0=300000.0000000001 +y_0=0 +ellps=GRS80 +datum=NAD83 +to_meter=0.3048006096012192 +no_defs')
spTransform(saf_spdf, CRS_obj)

我希望坐标会发生变化，但我不断收到错误消息
No transformation possible from NA reference system
我不知道为什么。我之前没有做过很多 CRS 转换。我认为上面的代码应该足以重现问题

Answer 1

proj4string (与 CRS 相同)未设置，这解释了错误:spTransform(): “No transformation possible from NA reference system” .
如果您检查 proj4string ，你会看到它是 NA .

coordinates(saf_spdf) <- ~STOP_LOCATION_X + STOP_LOCATION_Y
proj4string(saf_spdf)

返回:

[1] NA

您需要先 套装 proj4string这个对象，然后你可以 变换 它到纬度/经度 leaflet()需要。

# make data.frame a spatial object
coordinates(saf_spdf) <- ~STOP_LOCATION_X + STOP_LOCATION_Y

# SET the CRS of the object
proj4string(saf_spdf) <- CRS('the CRS of these coordinates as a character string')
# NOW we can transform to lat/lon
new <- spTransform(saf_spdf, CRS("+proj=longlat +ellps=WGS84 +datum=WGS84"))

# and finally, leaflet will accept this spatial object
new %>% leaflet()

这个错误背后的一些直觉:

Spatial transforms work like this: (1) R needs to know what reference system you're in to begin with; (2) once we know what the starting reference system is, then and only then can we transform those points into a new reference system. You're getting this error because you haven't specified WHERE to begin. You can't transform something if you don't know where it's starting from. This like asking a computer to "multiply by 5". We need something to "multiply" in the first place! Setting a CRS tells R where to start the transformation.