fxvpf: VPF Digest

A coverage-based interface, converting to nodes, polylines, polygons and text with or without column attributes.

The system is directory based, each directory (known as a dataset) containing sub-directories known as coverages (aka themes) which in turn contain tables (aka features). Selection may be made on any tables/features within any coverages/themes. Coverages have no inherent symbology, so the default fx symbology will be assigned to all graphic primitives.

Nothing is known about the projection or units of measure of VPF data. These must be set by the client if required.

Extensions to Standard Commands

query_tables

query_tables <client_string_array>

Returns the names of all tables in all datasets in the current directory and sub-directories. This list is also selectable by the following command:

iselect * from fxtables

select

select {* | <column>, … } from <table> where <conditions>

Selection can be on all, none or selected column attributes.

Additional Commands

point_column

point_column <column_name>

When retrieving point data, the default action is to create marker (node) graphic primitives. This command specifies a column from the non-graphic meta data, whose text values are to be used to create text primitives instead of marker primitives.

point_text

point_text <text>

When retrieving point data, the default action is to create marker (node) graphic primitives. This command specifies a constant text value to be used to create text primitives instead of marker primitives.

query_themes

query_themes { <client_string_array> { <client_string_array > } }

Returns to the client up to 2 sets of data:

the descriptions of all themes/coverages available in all datasets,
the select names of all themes/coverages.

If no parameters are supplied the information will simply be printed on the client.