Dear List,
I am trying to determine the speed an animal is traveling on each leg of a
track. My data is in longitude and latitude, so I am using the package rgdal to
convert it into a spatial points data frame and transform it to UTM. I would
then like to find the difference between successive longitudes and latitudes,
find the euclidean distance between points, and compute the speed of the animal
on each leg.
My problem is that once I convert the lat and long into a spatial points data
frame I can not access the lat and long individually. As far as I know I need
to convert them in order to transform the lat and long to UTM. Is there a way I
can call each variable separately in the sp dataframe? My code with example
data is below. Any suggestions would be appreciated.
library(rgdal)
date.diff<-(20,30,10,30)
Long<-c(-156.0540 ,-156.0541 ,-156.0550 ,-156.0640)
Lat<-c(19.73733,19.73734,19.73743,19.73833)
SP<-data.frame(Long,Lat)
SP<-SpatialPoints(SP,proj4string=CRS("+proj=longlat
+ellps=WGS84"))
SP.utm<-spTransform(SP, CRS("+proj=utm +zone=4 +ellps=WGS84"))
long.diff<-diff(SP.utm$Long)
lat.diff<-diff(SP.utm$Lat)
d=(long.diff^2+lat.diff^2)^.5
speed=d/date.diff
Aloha,
Tim
Tim Clark
Department of Zoology
University of Hawaii
If your goal is to get the distance between geographic points, you might try computing the distance along the "great circle arc" and forget about projection. Several packages have functions that do this. See https://stat.ethz.ch/pipermail/r-help/2007-October/144546.html. hope that helps, Ian Tim Clark wrote:> > > Dear List, > > I am trying to determine the speed an animal is traveling on each leg of a > track. My data is in longitude and latitude, so I am using the package > rgdal to convert it into a spatial points data frame and transform it to > UTM. I would then like to find the difference between successive > longitudes and latitudes, find the euclidean distance between points, and > compute the speed of the animal on each leg. > > [ removed from quote ] > > Aloha, > > Tim > > > > Tim Clark > Department of Zoology > University of Hawaii > > >-- View this message in context: http://www.nabble.com/Calculating-distance-between-spatial-points-tp24212875p24220923.html Sent from the R help mailing list archive at Nabble.com.
Hello, to call each variable separately, you can coerce your sp object back to a dataframe. The code below should to the job: DF.utm <- as.data.frame(SP.utm) long.diff<-diff(DF.utm$Long) Nicolas Tim Clark wrote:> > > Dear List, > > I am trying to determine the speed an animal is traveling on each leg of a > track. My data is in longitude and latitude, so I am using the package > rgdal to convert it into a spatial points data frame and transform it to > UTM. I would then like to find the difference between successive > longitudes and latitudes, find the euclidean distance between points, and > compute the speed of the animal on each leg. > > My problem is that once I convert the lat and long into a spatial points > data frame I can not access the lat and long individually. As far as I > know I need to convert them in order to transform the lat and long to UTM. > Is there a way I can call each variable separately in the sp dataframe? > My code with example data is below. Any suggestions would be appreciated. > > library(rgdal) > date.diff<-(20,30,10,30) > Long<-c(-156.0540 ,-156.0541 ,-156.0550 ,-156.0640) > Lat<-c(19.73733,19.73734,19.73743,19.73833) > > SP<-data.frame(Long,Lat) > SP<-SpatialPoints(SP,proj4string=CRS("+proj=longlat +ellps=WGS84")) > SP.utm<-spTransform(SP, CRS("+proj=utm +zone=4 +ellps=WGS84")) > > long.diff<-diff(SP.utm$Long) > lat.diff<-diff(SP.utm$Lat) > > d=(long.diff^2+lat.diff^2)^.5 > speed=d/date.diff > > > Aloha, > > Tim > > > > Tim Clark > Department of Zoology > University of Hawaii > > ______________________________________________ > R-help at r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > >-- View this message in context: http://www.nabble.com/Calculating-distance-between-spatial-points-tp24212875p24775433.html Sent from the R help mailing list archive at Nabble.com.