Data quality from GPS elevation

[meztez]

Negative elevation, most likely bad record has it is pretty hard to fly underground.

read_GPX <- function(file) {
  layers_data <- sf::st_layers(file)
  non_empty <- layers_data[["name"]][which(layers_data[["features"]] > 0)] |>
    setNames(nm = _)
    lapply(non_empty, sf::st_read, dsn = file, quiet = TRUE) |> 
      `class<-`("flightGPX")
}
dem_extract <- function(pts, method = c("simple", "bilinear"), ...) {
  method <- match.arg(method)
  dem <- 
    sf::st_bbox(pts) |> # simplify geometry to retrieve required dem
    sf::st_as_sfc() |> # recast to sfc to allow buffer around
    sf::st_buffer(units::set_units(50, m), nQuadSegs = 1) |> # add a margin to allow bilinear
    sf::st_bbox() |> # recompute bounding box before querying dem
    bcmaps::cded(aoi = _, ...) |> # obtain tiles
    terra::rast() # cast as raster
  terra::extract(
    x = dem, 
    y = sf::st_transform(pts, crs = sf::st_crs(dem)) |> terra::vect(),
    method = method,
    ID = FALSE
  )[,1]
}
#TODO: Investigate
# GPS Elevation not reliable unless you can fly below mountains?
f <- read_GPX("./data-raw/Heli data/NEH/2021/20220317-145549-0032969-139533.gpx")
pts <- f$track_points[3673:3713,] |> sf::st_geometry()
gps_ele <- f$track_points[3673:3713,]$ele
real_ele <- dem_extract(pts, method = "bilinear", check_tiles = FALSE)
leaflet::leaflet(pts) |> 
  leaflet::addProviderTiles("OpenTopoMap") |> 
  leaflet::addMarkers(
    label = sprintf(
      "<p>GPS Elevation: %s<br>DEM Elevation: %s</p>",
      gps_ele,
      round(real_ele, 2)
    ) |> lapply(FUN = htmltools::HTML)
  )

GPS : -90.2 DEM : 1691

Solution: Smooth, Moving Average?

[meztez]

For now, we will use a simple pmax(0, agl) as was done in the python code.

[meztez]

Approved, see meetings note