soilDB (version 2.5)

fetchSDA_spatial: Query SDA and Return Spatial Data

Description

This is a high-level fetch method that facilitates making spatial queries to Soil Data Access (SDA) based on `mukey` or `nationalmusym`. A typical SDA spatial query is made returning geometry and key identifying information about the mapunit. Additional columns from the mapunit table can be included using `add.fields` argument.

This function automatically "chunks" the input vector (using `soilDB::makeChunks`) of mapunit identifiers to minimize the likelihood of exceeding the SDA data request size. The number of chunks varies with the `chunk.size` setting and the length of your input vector. If you are working with many mapunits and/or large extents, you may need to decrease this number in order to have more chunks.

Usage

fetchSDA_spatial(x, by.col = "mukey", method = "feature",
  add.fields = NULL, chunk.size = 10)

Arguments

x

A vector of MUKEYs or national mapunit symbols.

by.col

Column name containing mapunit identifier ("mukey" or "nmusym"); default: "mukey"

method

geometry result type: 'feature' returns polygons, 'bbox' returns the bounding box of each polygon, and 'point' returns a single point within each polygon.

add.fields

Column names from `mapunit` table to add to result. Must specify table name prefix `mapunit` before column name (e.g. `mapunit.muname`).

chunk.size

How many queries should spatial request be divided into? Necessary for large results. Default: 10

Value

A Spatial*DataFrame corresponding to SDA spatial data for all MUKEYs / nmusyms requested. Default result contains mapunit delineation geometry with attribute table containing `gid`, `mukey` and `nationalmusym`, plus additional fields in result specified with `add.fields`.

Examples

# NOT RUN {
if(requireNamespace("curl") &
   curl::has_internet()) {

   # get spatial data for a single mukey
    single.mukey <- fetchSDA_spatial(x = "2924882")
    
    # demonstrate fetching full extent (multi-mukey) of national musym
    full.extent.nmusym <- fetchSDA_spatial(x = "2x8l5", by = "nmusym")
    
    # compare extent of nmusym to single mukey within it
    if(require(sp)) {
     plot(full.extent.nmusym, col = "RED",border=0)
     plot(single.mukey, add = TRUE, col = "BLUE", border=0)
    }
    
    # demo adding a field (`muname`) to attribute table of result
    head(fetchSDA_spatial(x = "2x8l5", by="nmusym", add.fields="muname"))
}
# }