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.
