load_tree_data() initial commit

Author: ctoney

NAMESPACE

@@ -3,5 +3,6 @@
 export(.get_tree_list_xy)
 export(create_fia_owin)
 export(create_fia_ppp)
+export(load_tree_data)
 export(overlay_crowns)
 export(predict_crwidth)

R/load_tree_data.R

@@ -0,0 +1,32 @@
+#' @noRd
+#' @export
+load_tree_data <- function(src, table = NULL, columns = NULL, sql = NULL) {
+
+    default_cols <- c("PLT_CN", "SUBP", "TREE", "AZIMUTH", "DIST", "STATUSCD",
+                      "SPCD", "DIA", "HT", "ACTUALHT", "CCLCD", "TPA_UNADJ")
+
+    if (is.null(columns))
+        columns <- default_cols
+
+    if (!is.null(sql) && !is.null(table))
+        stop("'table' and 'sql' are mutually exclusive", call. = FALSE)
+
+    ds <- NULL
+    if (is.null(table) && is.null(sql)) {
+        ds <- try(methods::new(gdalraster::GDALVector, src), silent = TRUE)
+    } else if (!is.null(table)) {
+        ds <- try(methods::new(gdalraster::GDALVector, src, table), silent = TRUE)
+    } else if (!is.null(sql)) {
+        ds <- try(methods::new(gdalraster::GDALVector, src, sql), silent = TRUE)
+    }
+
+    if (!methods::is(ds, "Rcpp_GDALVector"))
+        stop("failed to establish a connection to 'src'", call. = FALSE)
+
+    if (!is.null(table) && !is.null(columns) && columns != "")
+        ds$setSelectedFields(columns)
+
+
+
+    ds$close()
+}