There is a function "interpequal" in the trip package that provides a way to generate new points "equally spaced in time" between irregular track points. Obviously this can only be approximate depending on the spacing you want. The function also maintains the input points without change. This was used by a simplistic time-spent-in-cell method, that is now replaced by an exact method on the inter-point line segments using pixellate in the spatstat package.
That might be of interest, there are quite a lot of implications though - at least you must validate your data as a trip object to use that function as it is and I suggest the R-Sig-Geo or Animov mailing lists for exploring this question rather than R-help. Apart from trip and spatstat, the adehabitat family of packages (note that the original is now split into 4 separate replacement packages) is probably of more general interest to you. Cheers, Mike. On Tue, Jun 14, 2011 at 9:55 PM, anneloes de raad <anti...@hotmail.com> wrote: > > Dear help-list members, > > I am a student at Durham University (UK) conducting a PhD on spatial > representation in baboons. Currently, I'm analysing the effect of sampling > interval on home range calculations. > > I have followed the baboons for 234 days in the field, each day is > represented by about 1000 waypoints (x,y coordinates) recorded at irregular > time intervals. Consecutive waypoints in this raw data set have an average > distance interval of 5 meters an average time interval of 23 seconds (but > when baboons were stationary the time interval could be much larger - e.g. > waypoint 7 below).This raw data set needs to become a data set with waypoints > at regular intervals and thus, 'new' waypoints have to be 'created'. > Eventually, I want to use seven different time intervals: 2, 5, 10, 15, 30, > 45 and 60 minute intervals. I have tried in Excel, but I am not managing it. > I have some experience with R, and although I can 'read' quite complicated > scripts, I am unable to write them, so I would very much appreciate any help > anybody would be willing to offer me. > > > > My current data set has 9 columns (in csv / excel file): > x coordinate, y coordinate, year, month, day, record, time interval (duration > between this waypoint and the previous) (hh:dd:ss), summed time intervals, > distance interval (m) > > > EXAMPLE (24th of april 2007) > > (wp1) x1, y1, 2007, 7, 24, 1, 00:00:00, 00:00:00, 0 > (wp2) x2, y2, 2007, 7, 24, 2, 00:00:23, 00:00:23, 2 > (wp3) x3, y3, 2007, 7, 24, 3, 00:00:50, 00:00:73, 3 > (wp4) x4, y4, 2007, 7, 24, 4, 00:01:20, 00:02:33, 5 > (wp5) x5, y5, 2007, 7, 24, 5, 00:00:03, 00:02:36, 1 > (wp6) x6, y6, 2007, 7, 24, 6, 00:00:12, 00:02:48, 2 > (wp7) x7, y7, 2007, 7, 24, 7, 00:05:45, 00:08:33, 2 > > Now I need to change this data set into one with waypoints at regular > intervals: for example 2 minutes = 120 seconds >> 2 minutes after the first > waypoint (x1,y1) the baboons would be somewhere between WP3 and WP4 (at WP3 > sum duration is 73 seconds and after WP4 sum duration is 153 seconds), and so > this is where I would like a new waypoint created. Note that there are time > intervals which will be so large that multiple 'new' waypoints have to be > made / copied (e.g. WP 7 for a 2 minute interval). > > Three ways of calculating the new coordinates for this new waypoint from very > precise to not so precise (in order of preference) are: > > > > 1) Basing the new waypoint coordinates on the relative 'time distance' to > each waypoint of the two surrounding waypoints (therewith assuming a constant > movement during the time interval). The 'time distance' bewteen WP3 and WPnew > is (120-73) 47 seconds and the 'time distance' between WPnew and WP4 is > (153-120) 33 seconds (whereas total time interval between WP3 and WP4 is 80 > seconds). WPnew (with coordinates Xnew,Ynew) should then be located at > 80/33*100=41.25% from WP3: Xnew = X3 + (X4-X3)*41.25% and Ynew= Y3 + > (Y4-Y3)*41.25% > > > 2) Calculate the average location (average of x3,y3 and x4,y4), at which to > create a new waypoint at 2 minutes. > > > 3) A simpler alternative is that the location of the 'closer waypoint in > time', in this example WP 4, (WP4: 153-120=33 versus WP3: 120-73=47) could be > copied as being the new location. > > > > I hope I explained my query so that it makes sense to you. I realize I am > asking a 'big' question and apologize for this - the software programs I have > thorough knowledge of (ArcGIS, excel, Mapsource), are all unable to solve > this problem. I would be very grateful for any advice or suggestions. > > Best wishes, > Louise > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help@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. > -- Michael Sumner Institute for Marine and Antarctic Studies, University of Tasmania Hobart, Australia e-mail: mdsum...@gmail.com ______________________________________________ R-help@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.
