First, some examples to help get the flavour of the REF strings:
gdb:/pci/src/gen/irvine.pix/{IMG:3}
This is a reference to the third channel of the file /pci/demo/irvine.pix.
gdb:/{IMG:3}
This is a reference to the third channel of the current (base) file.
gdb:../irvine.pix/{VEC:5}
This is a reference to vector segment five (not necessarily the fifth vector
segment) on the file irvine.pix, which is one directory above the current
base file.
gdb:/{LUT:6}
This is a reference to LUT segment 6, in the current file.
gdb:/pci/demo/irvine.pixThis is a reference to the file /pci/demo/irvine.pix. Within the API, the layer type would be LAYER_FILE.
gdb:/{VEC:"FIELDBND"}
This is a reference to the vector segment in the current file with a layer
name of FIELDBND.Generally speaking, a GeoGateway Layer REF contains the following pieces.
REF class: Currently this is always "gdb:"; however, this should be treated as optional on input, in order that the layer ``/pci/demo/irvine.pix'' is the same as ``gdb:/pci/demo/irvine.pix''. The intention is that in the future, protocol specifiers like ``ftp://ftp.pci.on.ca/pub/irvine.pix'' can be used to refer to layers on the internet.
Filename: This is a filename in absolute or relative format. Either forward or backward slashes are considered acceptable as path component separators. It is unclear yet whether VMS or MacOS path formats will be acceptable. This field is optional; if omitted, the file of operation is implicitly the current one. Relative paths are interpreted relative to the path of the current file.
Layer Specifier: This takes the form ``/{layer_type:layer_id}''. The whole layer specifier is omitted for LAYER_FILE REF strings. The layer type is either IMG, or one of the three-letter segment type names. The layer_id is either a channel number, segment number, or layer name enclosed in double quotes.