| Safe Haskell | None |
|---|---|
| Language | Haskell2010 |
Ros.Topic.Stamped
Description
Functions for fusing Topics based on TimeStamp fields of the
underlying messages. This module shadows some of the functionality
of the Ros.TopicUtil module. The difference is that the functions
exported by this module use time stamps to correlate two
Topics.
The correlation uses a bracketing pair of values from one Topic
to pick a correspondance for each value from the other
Topic. This bracketing approach induces some latency. The most
common use case is calling the bothNew function with a Topic
that produces very quickly (faster than the minimum required update
rate), and another Topic that imposes a rate limit.
Documentation
everyNew :: (HasHeader a, HasHeader b) => Topic IO a -> Topic IO b -> IO (Topic IO (a, b)) Source
Returns a Topic that produces a new pair for every value
produced by either of the component Topics. The value of the
other element of the pair will be the element from the other
Topic with the nearest time stamp. The resulting Topic will
produce a new value at the rate of the faster component Topic.
interpolate :: (HasHeader a, HasHeader b) => (a -> a -> Double -> a) -> Topic IO a -> Topic IO b -> Topic IO (a, b) Source
The application interpolate f t1 t2 produces a new Topic that
pairs every element of t2 with an interpolation of two temporally
bracketing values from t1. The interpolation is effected with the
supplied function, f, that is given the two values to interpolate
and the linear ratio to find between them. This ratio is determined
by the time stamp of the intervening element of t2.
batch :: Double -> Topic IO a -> Topic IO [a] Source
Batch Topic values that arrive within the given time window
(expressed in seconds). When a value arrives, the window opens and
all values received within that window are returned in a list, then
the next value is awaited before opening the window again. Intended
usage is to gather approximately simultaneous events into
batches. Note that the times used to batch messages are arrival
times rather than time stamps. This is what lets us close the
window, rather than having to admit any message that ever arrives
with a compatible time stamp.