For forms with spatial types, such as geopoint, geotrace, or geoshape,
ruODK gives two options to access the captured spatial data.
Firstly, to make spatial data as simple and accessible as possible,
ruODK extracts the lat/lon/alt/acc from geopoints, as well as from the first coordinate of geotraces and geoshapes into separate columns. This works for both GeoJSON and WKT. The extracted columns are named as the original geofield appended with
Secondly, this vignette demonstrates how to turn the spatial data types returned from ODK Central into spatially enabled objects. To do so, we have to address two challenges.
The first challenge is to select which of the potentially many spatial fields which an ODK form can capture shall be used as the primary geometry of a native spatial object, such as an
sf SimpleFeature class. If several spatial fields are captured, it is up to the user to choose which field to use as primary geometry.
The second difficulty is that the parsed data from ODK Central is a plain table (
tbl_df) in which some columns contain spatial data. WKT is stored in text columns, GeoJSON is stored in list columns. This format is not recognised as a standard spatial input format.
The data shown in this vignette is hosted on the ODK Central Sandbox as one of the forms used in
ruODK package tests. The form contains every spatial widget supported by ODK Build for every supported spatial field type.
With working credentials to the ODK Sandbox, we can download the data directly.
# Set ruODK defaults to an ODK Central form, choose tz and verbosity ruODK::ru_setup( svc=paste0("https://sandbox.central.getodk.org/v1/projects/14/", "forms/build_Locations_1589344221.svc"), un = get_test_un(), pw = get_test_pw(), odkc_version = 0.8, tz = "Australia/Perth", verbose = TRUE) data_wkt <- ruODK::odata_submission_get(wkt = TRUE) data_gj <- ruODK::odata_submission_get(wkt = FALSE)
To allow users to build this vignette without credentials to the ODK Central Sandbox,
ruODK provides above form data also as package data.
We can turn data with a text column containing WKT into a SimpleFeatures object.
In addition, we can leave the
tbl_df as non-spatial object, and instead use the separately extracted latitude, longitude, altitude, and accuracy individually e.g. to plot a Leaflet map.
# Leaflet using sf leaflet::leaflet(data = geo_sf_point) %>% leaflet::addTiles() %>% leaflet::addMarkers(label = ~ device_id, popup = ~ device_id)
sf::st_as_sf on a text column containing a WKT geotrace.
# Leaflet using first extracted coordinate compoments from plain tbl_df # Note this represents the geotrace (line) with a simple point leaflet::leaflet(data = geo_wkt) %>% leaflet::addTiles() %>% leaflet::addMarkers( lng = ~ path_location_path_gps_longitude, lat = ~ path_location_path_gps_latitude, label = ~ device_id, popup = ~ device_id)
Again, we’ll use
sf::st_as_sf but select a WKT geoshape column.
# Leaflet using first extracted coordinate compoments from plain tbl_df # Note this represents the geoshape (polygon) with a simple point leaflet::leaflet(data = geo_wkt) %>% leaflet::addTiles() %>% leaflet::addMarkers( lng = ~ shape_location_shape_gps_longitude, lat = ~ shape_location_shape_gps_latitude, label = ~ device_id, popup = ~ device_id)
The above examples show how to turn spatial data into an
sf object, and give very rudimentary visualisation examples.
There are several other good entry points for all things R and spatial, including but not limited to:
The above list of examples and resources is far from comprehensive. Feel free to contribute or suggest other working examples for turning data from
ruODK into spatial formats.