mregions2 (version 1.1.2)

mrp_get: Get a data product

Description

Get a data product

Usage

mrp_get(
  layer,
  path = getOption("mregions2.download_path", tempdir()),
  cql_filter = NULL,
  filter = NULL,
  count = NULL
)

Value

An sf object with the Marine Regions data product

Arguments

layer

(character) Identifier of the data product. See mrp_list

path

(character) Path to save the requests. Default is base::tempdir(). See details.

cql_filter

(character) Contextual Query Language (CQL) filter. See details.

filter

(character) Standard OGC filter specification. See details.

count

(numeric) Maximum number of features to be retrieved.

Details

This function uses WFS services to download the Marine Regions layers as ESRI Shapefiles.

Caching

By default, the layers are downloaded to a temporal directory (base::tempdir()). You can provide a path in the path argument. But you can also set a path with # options("mregions2.download_path" = "my/path/").

Because it is possible to add filters, each request is identified with a crc32 hash, provided with digest::digest() and attached to the file downloaded.

Once a layer is downloaded, it will be read from the cache during the next two weeks. To avoid this, simply delete the layers in the cache path.

Filters

Both the Contextual Query Language (CQL) filter and the standard OGC filter specification allow to query the server before performing a request. This will boost performance as you will only retrieve the area of your interest. It is possible to query on attributes, but also perform geospatial queries. For instance, you can query a bounding box of interest.

CQL filters are possible only in geoserver. Marine Regions uses a geoserver instance to serve its data products. A tutorial on CQL filters is available in the geoserver web site.

See Also

mrp_list to describe the list of products, mrp_view() to visualize the data product in advance, mrp_colnames() and mrp_col_unique() to get the name, data type and unique values of a the columns of a data product, useful to query with the arguments cql_filter or filter

Examples

# \donttest{
# Set cache path. Default is a temporal directory
options(mregions2.download_path = tempdir())

getOption("mregions2.download_path")
#> [1] "/tmp/RtmpARLgoE"

# See the list of all data products
mrp_list

# We want the Exclusive Economic Zones of Portugal. Let's first visualize the product:
mrp_view("eez")

# See all the columns on this data product
mrp_colnames("eez")

# We should query on sovereign
# See all the possible values of sovereign1, sovereign2 and sovereign3
sov1 = mrp_col_unique("eez", "sovereign1")
sov2 = mrp_col_unique("eez", "sovereign2")
sov3 = mrp_col_unique("eez", "sovereign3")

# Is Portugal a value in the sovereign1, 2 and 3?
"Portugal" %in% sov1
#> [1] TRUE

"Portugal" %in% sov2
#> [1] FALSE

"Portugal" %in% sov3
#> [1] FALSE

# Portugal is only in sovereign1. Let's write a CQL filter to get only
# the EEZs of Portugal, or those where Portugal is a party of a dispute or a joint regime
portugal_eez <- mrp_get("eez", cql_filter = "sovereign1 = 'Portugal'")

# If you perform this request again, it will be read from the cache instead
portugal_eez <- mrp_get("eez", cql_filter = "sovereign1 = 'Portugal'")
#> Cache is fresh. Reading: /tmp/RtmpARLgoE/eez-1951c8b7/eez.shp
#> (Last Modified: 2023-04-24 17:45:16)

# You can also limit the number of features to be requested
mrp_get("eez", count = 5)
# }