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Fetch FWA Lakes

Source: R/frs_lake_fetch.R
frs_lake_fetch.Rd

Retrieve lake polygons from an FWA lakes table. Filter by watershed group code, blue line key, bounding box and/or area of interest.

Usage

frs_lake_fetch(
  conn,
  watershed_group_code = NULL,
  blue_line_key = NULL,
  bbox = NULL,
  area_ha_min = NULL,
  table = "whse_basemapping.fwa_lakes_poly",
  cols = c("waterbody_poly_id", "waterbody_key", "waterbody_type", "area_ha",
    "gnis_name_1", "blue_line_key", "watershed_group_code", "geom"),
  limit = NULL,
  aoi = NULL,
  simplify_m = NULL,
  order_by = "waterbody_poly_id"
)

Arguments

conn

A DBI::DBIConnection object (from frs_db_conn()).

watershed_group_code

Character. Watershed group code (e.g. "BULK"). Default NULL.

blue_line_key

Integer. Blue line key for lakes on a specific stream. Default NULL.

bbox

Numeric vector of length 4 (xmin, ymin, xmax, ymax) in BC Albers (EPSG:3005). Matches on envelope overlap (&&), so a lake whose envelope touches the box is returned even when the lake does not; use aoi for exact intersection. Default NULL.

area_ha_min

Numeric. Minimum lake area in hectares. Default NULL.

table

Character. Fully qualified table name. Default "whse_basemapping.fwa_lakes_poly".

cols

Character vector of column names to select. Default includes the most commonly used FWA lake attributes.

limit

Integer. Maximum rows to return. Default NULL (no limit).

aoi

Area of interest. An sf/sfc polygon (transformed to EPSG:3005, so it must carry a CRS) filters with ST_Intersects(). For WKT, pass sf::st_as_sfc(wkt, crs = 3005). Also accepts the other forms of frs_extract()'s aoi; its character form (watershed group codes) is an envelope prefilter, so use watershed_group_code to select groups. Default NULL.

simplify_m

Numeric. Simplification tolerance in metres, applied in the database. Drops M coordinates. Default NULL (full resolution).

order_by

Character vector. Columns to order rows by. Default "waterbody_poly_id", the FWA table's unique key; give another table's unique key (one or more columns) when table is changed, or NULL for no ORDER BY. With limit, the first limit rows in this order are returned.

Value

An sf data frame of lake polygons.

Details

Rows come back ordered by order_by (the table's unique key by default), so the same database returns the same sf on every call. For map layers, simplify_m simplifies in the database with ST_Normalize(ST_SimplifyPreserveTopology(geom, simplify_m)); ST_Normalize() fixes the order of parts, rings and ring start vertices so equal polygons serialise equally. area_ha is the stored, unsimplified area. Two databases on different GEOS versions can still simplify a ring differently, so a caller that saves the result should record postgis_full_version() with it.

See also

Other fetch: frs_stream_fetch(), frs_wetland_fetch()

Examples

if (FALSE) { # \dontrun{
conn <- frs_db_conn()
lakes <- frs_lake_fetch(conn, watershed_group_code = "BULK")
lakes_big <- frs_lake_fetch(conn, watershed_group_code = "BULK",
  area_ha_min = 10)

# Map layer: inside a watershed polygon, simplified to 25 m
ws <- frs_watershed_at_measure(conn, 360873822, 208877, simplify_m = 25)
lakes_map <- frs_lake_fetch(conn, aoi = ws, simplify_m = 25)
DBI::dbDisconnect(conn)
} # }