R/grid.R

In raffscallion/rapidfire: relatively accurate particulate information derived from inputs retrieved easily

# Tools to create an output grid for predection and pretty pictures. We can also
# just do the predictions at participant locations, but that requires
# running kriging and extraction every time a location changed.

# Make a grid for output predictions from an SPDF
make_grid <- function(spdf, cellsize) {
  box <- spdf@bbox
  xrange <- box[3] - box[1]
  yrange <- box[4] - box[2]
  xcells <- ceiling(xrange / cellsize)
  ycells <- ceiling(yrange / cellsize)

  x <- seq(1, xcells, by = 1) * cellsize + box[1]
  y <- seq(1, ycells, by = 1) * cellsize + box[2]

  df <- data.frame(Id = seq(1, length(x) * length(y), by = 1))

  grid <- sp::SpatialPointsDataFrame(cbind(rep(x, length(y)), rep(y, each = length(x))),
                        proj4string = sp::CRS("+init=epsg:3395"), data = df)
  sp::gridded(grid) <- TRUE
  return(grid)
}


# Make grid for output that covers an SPDF (such as a state or states)
make_state_grid <- function(outline, cellsize) {

  # Ensure we are in Mercator
  outline <- sp::spTransform(outline, sp::CRS("+init=epsg:3395"))

  # Get the bounding box
  box <- outline@bbox

  # create grid cells
  xrange <- box[3] - box[1]
  yrange <- box[4] - box[2]
  xcells <- ceiling(xrange / cellsize)
  ycells <- ceiling(yrange / cellsize)

  x <- seq(1, xcells, by = 1) * cellsize + box[1]
  y <- seq(1, ycells, by = 1) * cellsize + box[2]

  df <- data.frame(Id = seq(1, length(x) * length(y), by = 1))

  grid <- sp::SpatialPointsDataFrame(cbind(rep(x, length(y)), rep(y, each = length(x))),
                                     proj4string = sp::CRS("+init=epsg:3395"), data = df)

  # filter only to grid cells that fall within state (at least partially)
  stop("This function is currently inactive while rgeos is replaced")
  #g <- rgeos::gIntersection(grid, outline, byid = c(TRUE, FALSE))

  # Convert to spatial pixels
  sp::gridded(g) <- TRUE
  return(g)

}

# Get ids and lat/lons (in degrees) as a data frame from a grid for making assignements
grid_to_latlon <- function(grid) {

  df <- tibble::tibble(monitorID = grid@grid.index)
  deg <- sp::spTransform(grid, sp::CRS("+init=epsg:4326"))
  df$longitude <- deg@coords[,1]
  df$latitude <- deg@coords[,2]
  return(df)

}