# STI to STTDF with attributes computation

### Description

Converts a list of STI objects into a single STTDF object and computes some basic attributes of trajectory, including: distance, time lapsed, speed (km/h), change in elevation, change in moving direction between consecutive GPS points recorded. Also allows marking all attribute values with ID and trip.

### Usage

1 | ```
STItoSTTDF(list, id = NA, trip = NA, elev = NA)
``` |

### Arguments

`list` |
a list of STI objects. |

`id` |
A vector of IDs of GPS point record. If NA, numeric value "1" will be added as a dummy id for all GPS points. The length of the vector should be equal to the total number of GPS points in list. |

`trip` |
A vector of trip of GPS point record. If NA, numeric value "1" will be added as a dummy trip for all GPS points. The length of the vector should be equal to the total number of GPS points in list. |

`elev` |
A vector of levation of GPS point record. The length of the vector should be equal to the total number of GPS points in list. |

### Value

`sttdf`

return a single STTDF object with all attribute values stored in the data slot of STTDF object.

### Author(s)

Jinlong Yang - jinlong at psu.edu

### Examples

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | ```
lat <- runif(10, 39, 40)
long <- runif(10, 115, 116)
elev <- runif(10, 95, 100)
t1 <- "2008-10-24 02:09:59"
t2 <- "2008-10-24 02:10:08"
t1 <- as.POSIXct(t1, tz = "GMT")
t2 <- as.POSIXct(t2, tz = "GMT")
time <- seq(t1, t2, by = 1)
traj <- data.frame(lat, long, elev, time)
traj <- STI(SpatialPoints(traj[,2:1]), traj$time)
lst <- list()
lst[[1]] <- traj
STItoSTTDF(list = lst, elev = elev)
``` |

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