NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
Current content can be found at unidata.ucar.edu.
To learn about what's going on, see About the Archive Site.
------- Forwarded Message CC: visad-list@xxxxxxxxxxxxx Glenn, This is a perennial and interesting question. The developers guide says that MathType is not a synonym for class, since many different classes may be used for different approximations to the same MathType (e.g., a FieldImpl and a FlatField may have the same MathType). Further, Data classes may differentiate based on data source (e.g., the data form adapters define various new Data sub-classes, and remote Data also define some new Data sub-classes, and these may all have the same MathType). Furthermore, the same Data class may correspond to different MathTypes. For example, the RealTuple class corresponds to the MathTypes (latitude, longitude, altitude), (ir_radiance, vis_radiance), (time), and infinitely many others. Probably the main reason for having MathTypes is for the information they carry, including text names and distinct identities for different RealTypes, default Units for RealTypes, default CoordinateSystems for RealTupleTypes, and default Sets for RealTypes and RealTupleTypes. The distinct identities for different RealTypes plays a fundamental role in the VisAD visualization architecture, providing a handle for saying things like time is mapped to the X axis and temperature to the Y axis. If we used class for MathType, it would be hard to give distinct identities to different RealTypes. It has recently occurred to me to say that MathTypes are a lot like data base schemas. In fact, the differences between MathTypes and data base schemas can be traced to the distinction that data bases assume they model discrete things whereas VisAD models continuous things. I hope this clarifies the issue. As I said in my answer to John's question, one of the most pressing needs is VisAD extension packages that hide the complexity of the data model for users in specific disciplines or with specific tasks. Regards, Bill - ---------------------------------------------------------- Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI 53706 whibbard@xxxxxxxxxxxxx 608-263-4427 fax: 608-263-6738 http://www.ssec.wisc.edu/~billh/vis.html - ---------------------------------------------------------- Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI 53706 whibbard@xxxxxxxxxxxxx 608-263-4427 fax: 608-263-6738 http://www.ssec.wisc.edu/~billh/vis.html ------- End of Forwarded Message
visad archives: