Find the area, grid cells, or other zone that a building polygon overlaps or is located in. Implements an efficient spatial join by intersection.
zonalIndex(X, zone, zoneField = NULL, method = "centroid", returnObject = TRUE) # S3 method for sf zonalIndex(X, zone, zoneField = NULL, method = "centroid", returnObject = TRUE) # S3 method for sfc zonalIndex(X, zone, zoneField = NULL, method = "centroid", returnObject = TRUE) # S3 method for sp zonalIndex(X, zone, zoneField = NULL, method = "centroid", returnObject = TRUE) # S3 method for stars zonalIndex(X, zone, zoneField = NULL, method = "centroid", returnObject = TRUE) # S3 method for Raster zonalIndex(X, zone, zoneField = NULL, method = "centroid", returnObject = TRUE) # S3 method for character zonalIndex(X, zone, zoneField = NULL, method = "centroid", returnObject = TRUE)
| X | Spatial data (or path to file) with building footprint polygons |
|---|---|
| zone | Spatial data (or path to file) with polygon zones or a spatial grid (i.e. "raster") |
| zoneField | (Optional) Column name of unique identifiers in |
| method | One of |
| returnObject | Logical of whether to return an sf object of X with zonal
information. Default is |
'sf' object with attributes of X plus the unique zone ID or a
data.table with the row number to the record in X matched to
the zone IDs.
Zone assignments for building footprints can be done using three
possible methods, set by the method= parameter. Defining by
'centroid' allocates and entire building and its characteristics to the
zone(s) which its centroid intersects. Centroids are defined by
st_centroid which could be outside the polygon shape.
This is the default mode. Defining zones by 'intersect' uses the geometric
binary predicate from st_intersects. This method will
include a whole building and its characteristics into all zones that it
intersects. Therefore a building could appear to be "counted" twice. The
final approach, 'clip', uses st_intersection to split
footprints so that only that area of the polygon intersecting the zone is
include. This method is more time consuming because the geometries are
modified.
When zone is a multi-layer stars or Raster*,
zoneField can be used to select a specific layer to define the
areas, or NULL to use each pixel as a unique zone.
data("kampala", package="foot") buildings <- kampala$buildings clusters <- kampala$clusters # assign zones and return a new 'sf' object zonalIndex(buildings, clusters)#> Simple feature collection with 348 features and 2 fields #> Geometry type: POLYGON #> Dimension: XY #> Bounding box: xmin: 32.60631 ymin: 0.328119 xmax: 32.63543 ymax: 0.349785 #> Geodetic CRS: WGS 84 #> First 10 features: #> FID_1 zoneID geometry #> 1 6293 1 POLYGON ((32.60739 0.338599... #> 2 17706 1 POLYGON ((32.60662 0.339353... #> 3 29106 1 POLYGON ((32.60735 0.339238... #> 4 53393 1 POLYGON ((32.60778 0.339552... #> 5 57187 1 POLYGON ((32.60827 0.338821... #> 6 59496 1 POLYGON ((32.60698 0.339543... #> 7 68588 1 POLYGON ((32.60787 0.338906... #> 8 68590 1 POLYGON ((32.60774 0.339637... #> 9 72387 1 POLYGON ((32.60769 0.338973... #> 10 78504 1 POLYGON ((32.60703 0.338654...# assign all intersecting zones zonalIndex(buildings, clusters, method="intersect")#> Simple feature collection with 350 features and 2 fields #> Geometry type: POLYGON #> Dimension: XY #> Bounding box: xmin: 32.60631 ymin: 0.328119 xmax: 32.63543 ymax: 0.349785 #> Geodetic CRS: WGS 84 #> First 10 features: #> FID_1 zoneID geometry #> 1 6293 1 POLYGON ((32.60739 0.338599... #> 2 17706 1 POLYGON ((32.60662 0.339353... #> 3 29106 1 POLYGON ((32.60735 0.339238... #> 4 53393 1 POLYGON ((32.60778 0.339552... #> 5 57187 1 POLYGON ((32.60827 0.338821... #> 6 59496 1 POLYGON ((32.60698 0.339543... #> 7 68588 1 POLYGON ((32.60787 0.338906... #> 8 68590 1 POLYGON ((32.60774 0.339637... #> 9 72387 1 POLYGON ((32.60769 0.338973... #> 10 78504 1 POLYGON ((32.60703 0.338654...# return only a table of indices - note column names zonalIndex(buildings, clusters, zoneField="Id", returnObject=FALSE)#> xID Id #> 1: 97 1 #> 2: 242 1 #> 3: 390 1 #> 4: 712 1 #> 5: 762 1 #> --- #> 344: 3744 11 #> 345: 4127 11 #> 346: 4702 11 #> 347: 4788 11 #> 348: 4834 11