Fast way to find nearby points - For each frompoint, it finds distances to all nearby topoints (within radius)

Given a set of frompoints (e.g., facilities or blocks) and a specified radius in miles, this function quickly finds all the topoints (e.g., blocks or facilities) near each point. If from and to are facilities and census blocks, respectively, this can be used to aggregate over block groups near a facility for an EJAM analysis. But if it is used to define from as blocks and to as facilities, it finds all facilities near each block, which is how proxistat works to create proximity indicators.

Usage

getpointsnearbyviaQuadTree(
  frompoints,
  radius = 3,
  maxradius = 31.07,
  avoidorphans = FALSE,
  min_distance = 100/1760,
  retain_unadjusted_distance = TRUE,
  report_progress_every_n = 500,
  quiet = FALSE,
  quadtree,
  quaddatatable,
  updateProgress = NULL
)

Arguments

frompoints

data.table with columns lat, lon giving point locations of sites or facilities or blocks around which are circular buffers defined by radius.

• pointid is the indexed topoints id.

• ejam_uniq_id is the frompoints id

radius

in miles, defining circular buffer around a frompoint

maxradius

miles distance (max distance to check if not even 1 topoint is within radius)

avoidorphans

logical If TRUE, then where not even 1 topoint is within radius of a frompoint, it keeps looking past radius, up to maxradius, to find nearest 1 topoint

Note that if creating a proximity score, by contrast, you instead want to find nearest 1 SITE if none within radius of this BLOCK.

min_distance

miles minimum distance to use for cases where from and to points are identical or almost the same location.

retain_unadjusted_distance

set to FALSE to drop it and save memory/storage. If TRUE, the distance_unadjusted column will save the actual distance of site to the topoint, which might be zero. adjusted distance uses a lower limit, min_distance

report_progress_every_n

Reports progress to console after every n points

quiet

Optional.

quadtree

(a pointer to the large quadtree object) created using indexpoints() which uses the SearchTree package.

quaddatatable

data.table like quaddata passed to function

• the data.table used to create quadtree, such as blockpoints or frs.

updateProgress,

optional function to update Shiny progress bar

Details

The explanation below is assuming frompoints are "sites" such as facilities and topoints are Census blocks, but they can be reversed as long as the quaddata index passed is an index of the topoints.

For each point, this function uses the specified search radius and finds the distance to every topoint within the circle defined by the radius. Each topoint is defined by its latitude and longitude.

Results are the sites2points table that would be used by doaggregate(), with distance in miles as one output column of data.table.

See also

getpointsnearby()