[R] Class ltraj and function as.ltraj

[tandi perkins]

Hello R Help Group:

I have been struggling to create
an object of class ltraj with the function as.ltraj (adehabitatLT) with my bird
data.  Regarding my data structure, I
have GPS for 10 birds that transmit three times/day, over the course of a year
(with missing data).  I have a L10.csv
file with the following headers: Craneid, Date, Time, Long, Lat, Habitat, ID
(for burst).  

 

Step 1:  Bring in my data with: “stringsasFactors=FALSE” to convert all variables from Factor (except Lat/Long) to strings.  Thanks to David Carlson for that tip! Step 2: Transform my date, time vectors into POSIXct as follows: datetime=as.POSIXct(strptime(paste(L10$Date, L10$Time, sep=" "),format="%m/%d/%Y %H:%M:%S", "America/Chicago")) Thanks to Petr Pikal for that tip! Result: head(datetime)[1] "2011-07-10 17:00:38 CDT" "2011-07-11 00:01:06 CDT"[3] "2011-07-11 08:00:38 CDT" "2011-07-11 17:00:38 CDT"[5] "2011-07-12 00:01:06 CDT" "2011-07-12 08:00:38 CDT"   Good so far…. Step 3: Coord=L10[c("Longitude", "Latitude")]> head(Coord)  Longitude Latitude1    522598  33602852    522579  33601743    522618  33602744    522656  33601965    522397  33602076    522425  3360285 Good so far….now comes the tricky part for me. Step 4: Craneid=as.character(L10$Craneid)  id=as.character(L10$ID)

 

Step 5: Test=as.ltraj(Coord, datetime, Craneid, burst=id,
type=TRUE)

 

Drum Roll Please…. Error in
as.ltraj(Coord, datetime, Craneid, burst = id, typeII = TRUE) : 

 
non unique dates for a given burst

I include my data.frame for your
review.

 

head(l10b)

 
Longitude Latitude           
datetime               Craneid    id

1    522598 
3360285 2011-07-10 17:00:38  
L1_10 L1_10

2    522579 
3360174 2011-07-11 00:01:06  
L1_10 L1_10

3    522618 
3360274 2011-07-11 08:00:38  
L1_10 L1_10

4    522656 
3360196 2011-07-11 17:00:38  
L1_10 L1_10

5    522397 
3360207 2011-07-12 00:01:06  
L1_10 L1_10

6    522425 
3360285 2011-07-12 08:00:38  
L1_10 L1_10

 

  
Longitude Latitude           
datetime                     Craneid    id

3803    558205 
3346410 2011-04-15 17:00:38  
L5_10 L5_10

3804    552813 
3341251 2011-04-16 08:00:38  
L5_10 L5_10

3805    552784 
3341373 2011-04-28 08:00:38  
L5_10 L5_10

3806    552833 
3341262 2011-04-28 17:00:38  
L5_10 L5_10

3807    573502 
3407390 2011-06-21 17:00:38  
L8_10 L8_10

3808    573271 
3407499 2011-06-23 08:00:38  
L8_10 L8_10

 

I have checked and re-checked for
duplicates and there are no duplicates.  However,
when ask for duplicates in the datetime I get some “False” but a lot of “True’s”
So, I am thinking it has to do with the fact that R is not picking up the
individual birds which were monitored over the same time period.

 

How do I structure my data in R to recognize the 10 separate birds with their associated coordinates and time
stamps?

 

I would ultimately like to run
Bias Bridge Movement on these data but I can’t get from square one!  Help!  

 

Thanks in advance for any and all
assistance you can provide…You all are so valuable.  
TLP


 		 	   		  
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