McIDAS User's Guide
Version 2011.1

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Using Compressed Data Transfers

There are three ADDE data transfer methods available for sending data from remote servers to your client workstation. The methods are gzip-compressed, compressed, and uncompressed.

The gzip-compressed and compressed methods are most beneficial to users who transfer large data files or those with slow data connections. However, they only reduce the amount of data during the transfer; they do not change the resultant file size or accounting (the byte counts remain the same). For example, the destination file size from an IMGCOPY command is the same no matter which of the three methods you use. If most of the datasets you access are on a local network with fast transfer rates, then using the uncompressed method is probably best because it minimizes overhead.

The data transfer method you use on your client workstation is determined by the setting of its MCCOMPRESS environment variable. Because it's an environment variable, the method you select is the default for the entire McIDAS-X session. The only way to change the default method is to exit your McIDAS-X session, change the setting of MCCOMPRESS, then restart McIDAS-X. To override the default setting on a command-by-command basis, use the MCCOMPRESS global keyword with any ADDE command. See Appendix A, Global Keywords for more information.

Any client can use the compressed or uncompressed methods because all remote servers have the ability to send data using those methods. However you can use the gzip-compressed method only if all the remote servers you access are running version 2003 or later. If any of the remote servers are running a version prior to 2003 (or if you're unsure of the version), do not select gzip-compressed because if you request gzip-compressed transfers from a remote server running a version prior to 2003, your McIDAS-X command and the gunzip command waiting for data will fail.

If MCCOMPRESS is not set on your client workstation, or if it's set to NONE, then the uncompressed data transfer method is used. If you want to use the compressed data transfer method, enter the following Unix command (substitute the equivalent if using C shell) on your client workstation.


If you want to use the gzip-compressed data transfer method and you've verified that your client workstation and all the remote servers it accesses are running McIDAS-X 2003 or later, enter the following Unix command (substitute the equivalent if using C shell) on your client workstation.


If you want to set the environment variable each time you log on to your account, add the preferred command of the two above to your $HOME/.mcenv file and add the following line to your $HOME/.profile (ksh) or $HOME/.cshrc (csh) file. Be sure to leave a space between the period (.) and $HOME.

.  $HOME/.mcenv

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