tweak comments

data-raw/potential_fn_gradients.R

@@ -10,9 +10,11 @@ proj <- "+proj=merc +units=km +datum=WGS84"
 ## create world land raster
 wm <- rnaturalearth::ne_countries(scale = 10, returnclass = "sf")
 
+## set resolution to ensure a sufficiently small file size for the R pkg
+##  finer resolutions may be more useful for custom applications
 y <- terra::rast(crs = sf::st_crs(wm)$wkt,
           vals = 1,
-          resolution = c(0.25, 0.25),
+          resolution = c(0.25, 0.25),  
           xmin = -180,
           xmax = 180,
           ymin = -86,
@@ -27,13 +29,15 @@ x[is.na(x)] <- -1
 x[x == 1] <- NA
 x[x == -1] <- 1
 
-## calculate gradient rasters - these are needed to keep fish off land
+## calculate gradient rasters - these are needed to keep animals off land
 dist <- terra::distance(x)
 x1 <- terra::terrain(dist, v = "slope", unit = "radians")
 y1 <- terra::terrain(dist, v = "aspect", unit = "radians")
 grad.x <- -1 * x1 * cos(0.5 * pi - y1)
 grad.y <- -1 * x1 * sin(0.5 * pi - y1)
 grad <- c(grad.x, grad.y)
 
+## need to use terra::wrap() to export the rasters & terra::unwrap() to import 
+##     from an exported (wrapped) file
 grad <- terra::wrap(grad)
 save(grad, file = "inst/extdata/grad.rda", compress = "xz")