Pick each FDIS site visit's stream from the nearest snap and the streams its 1:50k code names
Source:R/fdis_place.R
knw_fdis_place.Rdscripts/0230 snaps every visit twice with fresh::frs_point_snap(): once
to the nearest stream, and once to each stream its FDIS 1:50k watershed code
names (the code's 20k blue_line_keys from fwa_streams_20k_50k, passed as
a hint, so that snap can land only on that stream). This function makes the
pick from the two results, with no database.
Arguments
- nearest
data.frame, one row per visit to place:site_visit,blue_line_key,downstream_route_measure,linear_feature_id,distance_to_stream, with the four position columns missing where no stream lies within the search.- hinted
data.frame, one row per visit and stream its code names:site_visit,hint_blue_line_key(the stream named) and the four position columns of the hinted snap, missing where that stream is not within the search. A visit with no row here has no code the cross-reference knows. Everysite_visitmust be innearest.- limit_near
numeric(1)metres: an unconfirmed pick farther than this is flaggedflag_far_snap.- limit_code
numeric(1)metres: a confirmed pick farther than this is flaggedflag_far_snap.
Value
A tibble, one row per row of nearest in its order: site_visit,
blue_line_key, downstream_route_measure, linear_feature_id,
distance_to_stream (the pick's), snap_method (code, nearest, or
NA when not placed), snap_confirmed, snap_moved,
nearest_distance_m, ws50_checked (the visit has a code the
cross-reference knows), flag_not_placed, flag_far_snap and
flag_ws50_mismatch. integer64 columns are refused: convert them with
as.numeric() first, as 0230 does.
Details
A visit whose code names a stream within the search takes the nearest such
stream (snap_method = "code", snap_confirmed = TRUE): the placement is
on a stream the code names, which is what 0230's check has always asked.
Where that stream is not the nearest one, the visit is moved to it
(snap_moved). A visit with no code the cross-reference knows takes the
nearest stream (snap_method = "nearest", unconfirmed). A visit whose code
names streams none of which lies within the search keeps the nearest
placement and is flagged flag_ws50_mismatch: the code contradicts every
stream in reach, so there is nothing to move it to.
A confirmed pick and an unconfirmed one are held to different limits,
because distance predicts a wrong stream only where nothing names the
stream: flag_far_snap marks an unconfirmed pick beyond limit_near and a
confirmed one beyond limit_code. Ties in distance go to the lowest
linear_feature_id, as in frs_point_snap().
The default limits are the ones 0230 uses, set by
data-raw/snap_limit_sensitivity.R (#91): 200 m, the widest distance band
whose code-checked disagreement stays under one in three, for an unconfirmed
pick, and the 500 m search radius for a confirmed one.
Examples
nearest <- data.frame(
site_visit = c("a", "b", "c"),
blue_line_key = c(1, 1, 2), downstream_route_measure = c(10, 50, 5),
linear_feature_id = c(11, 12, 21), distance_to_stream = c(4, 30, 150)
)
# b's code names stream 3, 60 m away; c's code names stream 2, its nearest
hinted <- data.frame(
site_visit = c("b", "c"), hint_blue_line_key = c(3, 2),
blue_line_key = c(3, 2), downstream_route_measure = c(80, 5),
linear_feature_id = c(31, 21), distance_to_stream = c(60, 150)
)
knw_fdis_place(nearest, hinted, limit_near = 100, limit_code = 500)
#> # A tibble: 3 × 13
#> site_visit blue_line_key downstream_route_measure linear_feature_id
#> <chr> <dbl> <dbl> <dbl>
#> 1 a 1 10 11
#> 2 b 3 80 31
#> 3 c 2 5 21
#> # ℹ 9 more variables: distance_to_stream <dbl>, snap_method <chr>,
#> # snap_confirmed <lgl>, snap_moved <lgl>, nearest_distance_m <dbl>,
#> # ws50_checked <lgl>, flag_not_placed <lgl>, flag_far_snap <lgl>,
#> # flag_ws50_mismatch <lgl>