Using grass for dynamic information, vector attributes

[Peter Olin]

	Grass users,

	forgive me if this is a frequently asked question.

	I am working on a project for traffic information and
	management where we among other things want to show the road
	network on the screen. The network is represented as vector
	data with a lot of attributes for each vector, where it is
	desirable to draw the vectors in different styles depending on
	the attributes (road class, speed limit, road width, one-way,
	etc). Some attributes like travel time and traffic flow are
	dynamically changed due to changes in the traffic situation,
	this needs to be visualized to the operator.

	In addition to just showing the data on the screen the
	operator needs to be able to interactively (on the map) change
	attributes for objects in the network, select subparts for
	closer inspection, change attributes for all vectors in an
	area, etc. The system will be highly interactive, driven by
	the user (asking for information and adding information) and
	external events (increased traffic flow reported by sensors, etc).

	I have looked at Grass for a while now, and to me it seems as
	if the high level programs are best suited for displaying
	statical data in a batch-like manner. The modular design for
	graphics drivers seems to make all drawing somewhat slow. The
	vector drawing seems pretty basic with small possibilities for
	changing appearance of the vectors.  Updating parts of the map
	seems difficult.

	Since Grass have a lot of features that is of interest to us,
	I would be interested in understanding to what extent Grass
	can be used (if at all) in our project. 

	So, to be more concrete, has anyone of you Grass users had any
	experience with the following:

	* Using Grass for continuously displaying changing information
	on a map. 

	* More advanced vector drawing, using database attributes to
	determine vector appearance.

	* "Advance", user-oriented interaction. Integrating the Grass
	maps with other X-windows/widgets/clients.

	All comments are gratefully received. If you answer on the
	list, fine with me. If you mail me I promise to summarize the
	responses.

	/Peter

---------
Peter Olin                            ! Email: olin at sics.se
Swedish Institute of Computer Science ! Tel: +46 8 752 1557 (direct)
Box 1263                              !  or: +46 8 752 1500
S-164 28 KISTA, SWEDEN                ! Fax: +46 8 751 7230