Update README.md

README.md

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 # Fluvial Transport
 
-This app calculates the transport distance along a stream.
+This app calculates the transport distance along a stream or other route.
 It is designed for tracking RFID tracers across multiple survey dates.
 
-It works by assigning a location along the stream centerline for each tracer on each date. Then the distance between locations is calculated for each tracer between all dates.
-A total distance traveled is also calculated.
+It works by assigning a location along the stream centerline for each tracer on each date. Then the distance between locations is calculated for each tracer between all dates. The scrpit relies on the `sf` and `sfnetworks` for spatial data hadnling and `data.table` for other data processing.
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+A total distance traveled is determined by selecting the maximum distance moved from all date pairs. Because a tracer may not be found in all survey dates, `NA` values are returned when a tracer is missing from a particular survey.
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+Processing times when using many files can be very slow.
 
 Example data from surveys on Amethyst Brook, MA is provided.
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+Input files should be preprocessed to have a standardized tracer identification column, date column, and coordinate columns. See the example data for examples.