Extend DescribeFeatureType methods to support multiple typeNames

[Maëlle Salmon]

• Could one get all feature types at once? At the moment it seems one can only get the feature type per feature, but a request like https://geo.vliz.be/geoserver/Dataportal/wfs?SERVICE=WFS&REQUEST=DescribeFeatureType&VERSION=2.0.0 actually exists.
• From that URL above some layers are "complexType" and some are "element". Could that help guessing the output format? In that case the one that are "elements" are the one sf::st_read() (that's used in ows4R) returns a data.frame.

The context is that I'm wondering how we could get more info on what we're going to get before using getFeatures() itself.

Thanks in advance!

[Maëlle Salmon]

I think I misread what the element vs complexType are, however I'm still wondering whether the metadata could help one see what's geographical (sf) vs not (data.frame).

[Emmanuel Blondel]

DescribeFeatureType should target 0..* cardinality for typeNames , as part of the WFS spec, so in principle we should be able to implement it. Possibly the same for GetFeatures, but i can't work on it immediatly. In general DescribeFeatureType and GetFeature are not used on more than one typeNames, although it is possible in the standard model.

You can get information of feature type before doing Get Feature, you do it when finding/accessing a feature type where a DescribeFeatureType operation is done when triggering getDescription() method.

For example

wfs <- WFSClient$new("https://www.fao.org/fishery/geoserver/wfs", "2.0.0", logger = "INFO")
fao_areas <- wfs$capabilities$findFeatureTypeByName("fifao:FAO_MAJOR")
fao_areas_desc <- fao_areas$getDescription(pretty = T)

[Maëlle Salmon]

Thank you!

Oh right and if none of the types is "geometry" then one can conclude it'll be a data.frame, correct?

[Emmanuel Blondel]

Yes ows4R behaves like that. You can publish (in particular in Geoserver) geometryless data through WFS protocol, ows4R will retrieve a data.frame instead of a sf object.

[Emmanuel Blondel]

You can still filter over the properties you want to be part of the output with the WFS propertyName parameter. See below an exampe where I skip the geometry:

fao_areas_data = fao_areas$getFeatures(propertyName = "F_CODE,F_LEVEL")

[Maëlle Salmon]

Thanks!

Is this "type guessing before download" something that should happen in ows4R (like getTitle() there could be getRType() or so) or in EMODnetWFS?

[Emmanuel Blondel]

The type is the R type already. The guessing is done in https://github.com/eblondel/ows4R/blob/master/R/WFSFeatureTypeElement.R#L119. For backward compatibility reasons, I can't really change the method now so getType will give the R type, but if you need the WFS type, I can add a method getNativeType or something similar

fao_areas_desc <- fao_areas$getDescription(pretty = F)
will give you the raw list of WFSFeatureTypeElement from which you can apply the getType. The above with pretty = T is just a convenience to get tabular view over the feature type definition

[Maëlle Salmon]

I think by type I meant layer type actually. I.e. knowing in advance when we do getFeatures(), if the resulting thing will be a data.frame or a sf. Sorry for getting this mixed up.

[Maëlle Salmon]

Example:

library("EMODnetWFS")
wfs <- emodnet_init_wfs_client(
    service = "biology_occurrence_data"
)
#> Loading ISO 19139 XML schemas...
#> Loading ISO 19115 codelists...
#> Loading IANA mime types...
#> No encoding supplied: defaulting to UTF-8.
#> ✓ WFS client created succesfully
#> ℹ Service: 'http://geo.vliz.be/geoserver/Dataportal/wfs'
#> ℹ Version: '2.0.0'

layers <- emodnet_get_wfs_info(wfs)[["layer_name"]]

is_geom <- function(layer_name, wfs) {
    layer <- wfs$capabilities$findFeatureTypeByName(sprintf("Dataportal:%s", layer_name)) 
    geom <- any(layer$getDescription(pretty = T)$type == "geometry")
    tibble::tibble(
        layer = layer_name,
        geom = geom
    )
} 

layers_info <- purrr::map_df(layers, is_geom, wfs = wfs)
knitr::kable(layers_info)

layer	geom
abiotic_observations	TRUE
biotic_observations	TRUE
eurobis-obisenv_basic	FALSE
eurobis-obisenv_count	FALSE
eurobis-obisenv_full	TRUE
eurobis-obisenv	TRUE
eurobis_grid_15m-obisenv	TRUE
eurobis_grid_1d-obisenv	TRUE
eurobis_grid_30m-obisenv	TRUE
eurobis_grid_6m-obisenv	TRUE
eurobis_points-obisenv	TRUE
iucn_grid	TRUE
abiotic_observations_count	FALSE
biotic_observations_count	FALSE
categories	FALSE
categories_get_by_datatype	FALSE
datafiches_get_by_datasource_and_dataorigin_and_datatype	FALSE
dataorigin_get_by_datasource_and_datatype	FALSE
dataportal_get_observations_where	TRUE
dataproviders_get_by_datatype	FALSE
datasets	FALSE
eurobis	TRUE
geoobjects	TRUE
geoobjects_get_by_name	FALSE
parameters	FALSE
parameters_get_by_name_and_category	FALSE
taxa	FALSE

^{Created on 2022-03-11 by the reprex package (v2.0.1)}