Spatial Data Table

Summary

A spatial.data.table object is an extension of data.table. All the usual operations on a data.table (should) work within a spatial.data.table too. If not, please let me know by filing an issue.

This package includes convenience functions for doing spatial calculations with data in data.table and spatial.data.table objects. Notably I have re-written a set of geosphere::dist_ functions in C++ (using Rcpp) by stripping out some of the unnecessary matrix-conversions. The functions also work in the j argument of data.table, so as per usual data.table operations you only have to pass in un-quoted column names.

You can also

• convert sp and sf objects into spatial.data.table using toSDT()
• encod sf objects (LINESTRINGS, POLYGONS and MULTIPOLYGONS) into polylines (Google's polyline) using EncodeSF()

Installation

Install the developent version using devtools

devtools::install_github("SymbolixAU/spatialdatatable")

Why I made this package

The driving factor behind developing spatialdatatable was to simplify the process of doing distance calculations within a data.table, which was driven by writing an efficient haversine calculation that falls naturally within the j argument of data.table.

I also wanted to make use of Google's Encoded Polyline format for storing lines and polygons. The benefit of which is reduced object size

library(sf)

## example data that comes with the sf library
filename <- system.file("shape/nc.shp", package="sf")
sf <- st_read(filename)

object.size(sf)
135168 bytes

sdt <- EncodeSF(sf)

object.size(sdt)
50032 bytes

The EncodeSF() function takes the geometry information from the sf object and encodes it using Google's encoding algorithm (without losing any of the other data), and then stores it in a spatial.data.table object.

sf
# Simple feature collection with 2 features and 1 field
# geometry type:  LINESTRING
# dimension:      XY
# bbox:           xmin: -80.19 ymin: 18.466 xmax: -64.757 ymax: 32.321
# epsg (SRID):    NA
# proj4string:    NA
#      id                        sf_line
# 1 line1 LINESTRING(-80.19 25.774, -...
# 2 line2 LINESTRING(-70.579 28.745, ...

sdt[1:5, .(.id, lineId, hole, NAME, polyline)]
#    .id lineId  hole      NAME                polyline
# 1:   1      1 FALSE      Ashe u_d|EtsgpNmmFphLyEbc...
# 2:   2      1 FALSE Alleghany or}|EhdznNyvA~Ce_Dli...
# 3:   3      1 FALSE     Surry }re|EbcajNakAf|BqKby...
# 4:   4      1 FALSE Currituck mtt|E`o|nMkpBhs@~I``...
# 5:   4      1 FALSE Currituck m~b~Ev``oMJcqDfwAe}O...