vmask | R Documentation |
This function filters location data obtained from Argos, using the MacConnell al. (1992) algorithm.
vmask(lat, lon, dtime, vmax)
lat |
a numeric vector of latitudes, in decimal degrees |
lon |
a numeric vector of longitudes, in decimal degrees |
dtime |
a vector of class POSIXct with date and time for each location |
vmax |
speed threshold, in m/s |
Locations are filtered using the algorithm described in MacConnell et al. (1992). Since this algorithm calculates for each location the root mean square (rms) of the speeds to the previous, 2nd previous, next and 2nd next location, high swimming speeds can be obtained for points that are adjacent to outlier locations. Therefore, when the algorithm is applied to a set of locations, only the peaks in rms (that are above the maximum speed) are removed. Other locations are not removed even if above the speed limit. rms is then recalculated n times until all locations are below the speed threshold.
Returns a vector with the following elements: "removed"
(location removed by the filter),
"not"
(location not removed) and "end_location"
(location at the end
of the track where the algorithm could not be applied).
Carla Freitas
McConnell, B.J., Chambers, C. and Fedak, M.A. (1992) Foraging ecology of southern elephant seals in relation to the bathymetry and productivity of the Southern Ocean. Antarctic Science 4:393-398.
sdafilter
data(seal) lat<-seal$lat lon<-seal$lon dtime<-seal$dtime lc<-seal$lc # filter by speed mfilter<-vmask(lat,lon,dtime,2) # plot unfiltered (grey) and filtered data (green) plot(lon,lat,col="lightgrey",type="l",xlim=c(5,18), ylim=c(77.1,79.1),xlab="Longitude",ylab="Latitude") lines(lon[which(mfilter=="not")],lat[which(mfilter=="not")],col="darkgreen")
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.