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

Bart kranstauber at orn.mpg.de
Thu Aug 3 11:14:01 CEST 2017

Dear Alice,

Since Move inherits a SpatialPointsDataFrame the finding the location 
furthers away can be done as follows (under the assumption the data are 
longlat and the caveat pointed out by Barry):

 > require(move)
 > data(leroy)
 > which.max(spDistsN1(leroy, c(-40,40), longlat=T))
[1] 600



On 03.08.2017 10:00, Michael Sumner wrote:
> Also, trip is really outdated and dopey and homedist is likely not working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>
> wrote:
>> 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!
>>>          [[alternative HTML version deleted]]
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