[R-sig-Geo] average bearing of animal movement data

Michael Sumner mdsumner at gmail.com
Thu Aug 3 10:00:45 CEST 2017

Also, trip is really outdated and dopey and homedist is likely not working
properly, very happy to help find he answers here there are many options.

Cheers, Mike at tripIsMyFault.org

On Thu, 3 Aug 2017, 17:27 Barry Rowlingson, <b.rowlingson at lancaster.ac.uk>

> You can convert a "trip" object to a SpatialPointsDataFrame with
> as("SpatialPointsDataFrame",my_trip). Then you can use functions like
> "spDistsN1" from sp to compute the distance from "home" to each point,
> find the maximum, and then use "bearing" from the "geosphere" package
> to get the bearing for that row.
> A complication I see is that this will only return the maximum
> distance to a vertex point on the trip. For a trip in two flat
> dimensions the maximum distance will always be a vertex point on the
> trip but I think on a sphere its possible for great circles between
> two points to have a location on the circle that is further from a
> given point than either of the end points. But I can't get my head
> quite round the 3d triangular geometry this early in the morning. For
> small steps in a trip where you can approximate the geometry as flat
> this is not a problem.
> In contrast, the minimum distance from a trip to a "home" point is
> rarely a vertex point on the trip because its possible for the trip
> path to go very close to the home point in question. e.g a trip from
> (10,0) to (-10,0) goes right through (0,0) but its points are both 10
> units away.
> Barry
> On Wed, Aug 2, 2017 at 7:25 PM, Alice Domalik <adomalik at sfu.ca> wrote:
> > Hi there,
> >
> > I have seabird tracking data and I have used both the packages 'trip'
> and 'move' to calculate the max distance travelled (using the function
> 'homedist' in 'trip', and 'distanceSummary' in 'move').
> > I would also like to describe the bearing of each animal when it is at
> its maximum displacement from the colony. I am wondering if anyone knows
> any packages that can calculate this. Alternatively, if someone knows how I
> can extract the coordinates of the location of maximum displacement.
> >
> > thanks so much!
> >
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> >
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Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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