watersurfaces_refpoints: reference points for the watersurfaces_hab polygons

watersurfaces_refpoints is a data source that reflects spatial points in the Belgian Lambert 72 coordinate reference system (EPSG-code 31370). Each point uniquely represents one polygon of the watersurfaces_hab data source.

watersurfaces_refpoints is designed to 'only grow', i.e. rows are added to represent new polygon_id values from new watersurfaces_hab versions, and rows from a previous version are kept. Care is taken to recycle the same point for different polygon_id values if the latter represent the same location across different watersurfaces_hab versions.

The data source is composed of two text files, watersurfaces_refpoints.tsv and watersurfaces_refpoints.yml,  written by the R package git2rdata. The corresponding R data frame can be reproduced using the same package.

See R-code in the 'n2khab-mhq-design' GitHub repository for the creation starting from version watersurfaces_refpoints_v4, and from version watersurfaces_hab_v5 of the watersurfaces_hab data source.

A reading function is provided by the R-package n2khab to return the data source in a standardized way in the R environment, either as a data frame or as a spatial object, by default filtered according to a specific version of watersurfaces_hab.

Columns of the dataset:

• polygon_id: the polygon_id from watersurfaces_hab, either version watersurfaces_hab_v5 or older
• grts_ranking: the GRTS address of the point as derived from the GRTSmaster_habitats data source
• in_object: did the point fall within the corresponding polygon at the time of creation? Note that the polygon's geometry may have changed since then; it may not currently hold.
• x: easting coordinate of the point (EPSG:31370)
• y: northing coordinate of the point (EPSG:31370)