Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Feature suggestion: add get_profile_elev() function for returning elevation along a line #93

Open
elipousson opened this issue Nov 3, 2023 · 1 comment
Open

Feature suggestion: add get_profile_elev() function for returning elevation along a line #93

elipousson opened this issue Nov 3, 2023 · 1 comment

Comments

@elipousson
Copy link

Thanks for the handy package! I was wondering if you may be interested in a get_profile_elev() function that uses sf::st_line_sample() to get points along a line before calling elevatr::get_elev_point() and optionally get distance between points on the line. I put together a prototype that I think works pretty well – let me know if you're interested and I'd be happy to open a pull request.

library(sf)
#> Linking to GEOS 3.11.0, GDAL 3.5.3, PROJ 9.1.0; sf_use_s2() is TRUE
library(elevatr)
#> elevatr v0.99.0 NOTE: Version 0.99.0 of 'elevatr' uses 'sf' and 'terra'.  Use 
#> of the 'sp', 'raster', and underlying 'rgdal' packages by 'elevatr' is being 
#> deprecated; however, get_elev_raster continues to return a RasterLayer.  This 
#> will be dropped in future versions, so please plan accordingly.
library(ggplot2)

get_profile_elev <- function(locations,
                             units = NULL,
                             dist = FALSE,
                             n = NULL,
                             density = NULL,
                             type = "regular",
                             sample = NULL,
                             ...,
                             keep_units = FALSE,
                             cumulative = FALSE) {
  if (!inherits(locations, "sf")) {
    locations <- sf::st_as_sf(locations)
  }

  if (is.numeric(sample) || is.numeric(n) || is.numeric(density)) {
    locations <- sf::st_line_sample(
      locations,
      n = n, density = density,
      sample = sample, type = type
    )

    locations <- sf::st_cast(locations, to = "POINT")
  } else if (!sf::st_is(locations, "POINT")) {
    locations <- suppressWarnings(sf::st_cast(locations, to = "POINT"))
  }

  location_coords <- as.data.frame(sf::st_coordinates(locations))
  location_coords <- setNames(location_coords, tolower(names(location_coords)))
  locations_crs <- sf::st_crs(locations)

  elev_point <- elevatr::get_elev_point(location_coords, prj = locations_crs)

  if (nrow(elev_point) < 2) {
    dist <- FALSE
  }

  if (dist) {
    dist_point <- 0
    elev_point_geom <- vctrs::vec_chop(sf::st_geometry(elev_point))

    for (i in (seq(length(elev_point_geom) - 1))) {
      dist_add <- sf::st_distance(
        elev_point_geom[[i]],
        elev_point_geom[[i + 1]]
      )

      dist_point <- c(dist_point, dist_add)
    }

    if (cumulative) {
      dist_point <- cumsum(dist_point)
    }

    elev_point[["distance"]] <- units::set_units(
      dist_point, locations_crs$units_gdal,
      mode = "standard"
    )
  }

  elev_units <- unique(elev_point[["elev_units"]])

  if (!is.null(units)) {
    mode <- "standard"
    elev_units_label <- units

    if (!is.character(units)) {
      elev_units_label <- unique(as.character(base::units(x)[["numerator"]]))
      mode <- units::units_options("set_units_mode")
    }

    elev_point[["elevation"]] <- units::as_units(
      elev_point[["elevation"]],
      elev_units
    )

    elev_point[["elevation"]] <- units::set_units(
      elev_point[["elevation"]],
      value = units, mode = mode
    )

    elev_point[["elev_units"]] <- elev_units_label

    if (dist) {
      elev_point[["distance"]] <- units::set_units(
        elev_point[["distance"]],
        value = units, mode = mode
      )
    }
  } else if (dist) {
    elev_point[["distance"]] <- units::set_units(
      elev_point[["distance"]], elev_units
    )
  }

  if (!keep_units) {
    elev_point[["elevation"]] <- units::drop_units(elev_point[["elevation"]])

    if (dist) {
      elev_point[["distance"]] <- units::drop_units(elev_point[["distance"]])
    }
  }

  elev_point
}

nc <- st_read(system.file("shape/nc.shp", package = "sf")) |>
  st_transform(3857)
#> Reading layer `nc' from data source 
#>   `/Library/Frameworks/R.framework/Versions/4.3-arm64/Resources/library/sf/shape/nc.shp' 
#>   using driver `ESRI Shapefile'
#> Simple feature collection with 100 features and 14 fields
#> Geometry type: MULTIPOLYGON
#> Dimension:     XY
#> Bounding box:  xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS:  NAD27

nc_line <- suppressWarnings(
  st_cast(
    st_union(
      st_centroid(nc[1, ]),
      st_centroid(nc[2, ])
    ),
    to = "LINESTRING"
  )
)

elev_profile <- get_profile_elev(
  nc_line,
  units = "ft",
  dist = TRUE,
  cumulative = TRUE,
  n = 15
)
#> Downloading point elevations:
#> Note: Elevation units are in meters

elev_profile |>
  ggplot(aes(distance, elevation)) +
  geom_area() +
  scale_x_continuous(labels = scales::label_number()) +
  labs(
    x = "Distance (ft.)",
    y = "Elevation (ft.)"
  )

Created on 2023-11-03 with reprex v2.0.2
@pnogas67
Copy link

pnogas67 commented Nov 3, 2023 via email

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Assignees
No one assigned
Labels
None yet
Projects
None yet
Milestone
No milestone
Development

No branches or pull requests
2 participants
@elipousson @pnogas67