6.1 Differences between FreeForm ND and the OPeNDAP FreeForm ND Data Handler

The OPeNDAP FreeForm ND Data Handler is based on the same libraries used to make the FreeForm ND utilities. However, there are some important differences in the resulting software:

• The OPeNDAP FreeForm ND Data Handler is a FreeForm ND application that converts data on receiving a client request for that data, and not before. Data served by the OPeNDAP FreeForm ND Data Handler remains in its original format.
• The OPeNDAP FreeForm ND Data Handler does not produce an output file containing the converted data, but serves it directly over the network to the DAP2 client. Therefore, the OPeNDAP FreeForm ND Data Handler ignores the output section of the format definition file.
• To sample a data file, you do not write format definitions that cause the FreeForm ND engine to sample the data file. Instead, you add a DAP2 "constraint expression" to the URL that the client sends to the OPeNDAP FreeForm ND Data Handler.
• The OPeNDAP FreeForm ND Data Handler performs data conversion on the fly. Conversion only takes place when the client sends a URL requesting data from the OPeNDAP FreeForm ND Data Handler.
• Unlike FreeForm ND, there is no static file created by the conversion. (If you wish to create or work with such a file, use the FreeForm ND utilities, such as newform.)