grab_nodes: Filter a pixel cloud
In markwh/rivertile: R interface for SWOT rivertile data

Only include pixels assigned to a given vector of nodes.

grab_nodes(pixdf, nodeids, pcvdf = pixdf)

grab_nodebox(pixdf, nodeids, pcvdf = pixdf, dilate = 0)

rt_nodebbox(pixdf, nodeids, pcvdf = pixdf, dilate_frac = 0)

grab_bbox(pixdf, bbox)

`pixdf`	as returned by `pixc_read()` or `pixc_join()`
`nodeids`	values of node_index to keep
`pcvdf`	a data.frame that includes node and range/azimuth information, e.g. as returned by `pixcvec_read()`. May be omitted if this information is already in `pixdf`
`dilate`	Number of pixels to extend beyond the supplied nodes (default is 0).
`dilate_frac`	fraction of lat/lon range to dilate the bounding box (applied on both sides)
`bbox`	as returned by `rt_nodebbox()`

grab_nodebox: Filter to a range/azimuth bounding box.
rt_nodebbox: Create a lat/lon bounding box.
grab_bbox: Filter to a lat/lon bounding box.