index.to.gxgy {CTFS} | R Documentation

## Converts a Quadrate Number to GX GY Coordinates

### Description

This function takes a quadrate (index) number and returns the x, y plot location of the quadrate corner. The corner is the southwest or lower left of the quadrate. The quadrate is based on a gridsize that by default divides the plot into 20 by 20 m squares. The gridsize can be defined by the user so other quadrate sizes can be used. The far edges of the plot are considered out-of-bounds. The inverse function is `gxgy.to.index`.

### Usage

    index.to.gxgy(index, gridsize = 20, plotdim = c(1000, 500))

### Arguments

`index` | quadrate, valid default values 1 to 1250
`gridsize` | side of the square quadrate, 20 x 20m by default
`plotdim` | dimensions of the plot: east-west 1000m and north-south 500m

### Details

The function should work for any 4 sided plot, square or rectangular. The convention is 20 by 20 m quadrates, 1250 of them in a 1000 by 500 m plot. The convention is to number the quadrates starting in the southwest corner and going northward up a "column" of 25, and returning to the southern border for 26-50, etc. The columns are numbered 1 to 50, west to east (left to right). The rows are numbered 1 to 25, south to north (bottom to top).

### Value

Returns a data frame which contains the x and y coordinate of the southwest (or lower left) corner of the quadrate provided. Returns NA when an invalid quadrate is given.

### Author(s)

Rick Condit, Suzanne Lao and Pamela Hall

### See Also

`CTFS.quadfunctions`

### Examples

    ## Not run:

    tst.corners=c(1,25,1226,1250)
    index.to.gxgy(tst.corners)

    # invalid index
    index.to.gxgy(1251)
    ## End(Not run)

[Package CTFS version 1.00 Index]