Unzipping Data - FAQ
This page has been written to help users extract the data they download from Landmap.
What is a zip file and why use it?
Are there different formats of zip file?
what do you need to do to get at the data you have just downloaded?
Where can I download a program which extracts zip files so I can get to my satellite data?
Q. What is a zip file and why use it?
A. The ZIP file format is a data compression and archival format. A ZIP file contains one or more files that have been compressed to reduce their file size.
Q. Are there different formats of zip file?
A. Yes, three different zip fomates;
GZIP format is the native zipping format for UNIX / Linux / Solaris. All files zipped using the gzip program end in the .gz prefix. Gzip is used by the Landmap website to reduce the size of your download, by as much as 90% in certain cases!
Windows ZIP Some data (mostly the raw dataset downloads) has been zipped using WinZip. This is a freeware application that runs under the windows platform. WinZip can take lots of files, compress them all, and store them in a single file, with a .zip extension.
TAR is a UNIX program that is used to group several files together under UNIX. Directory structures will be used when unzipping the data. Tar does not zip the file that it produces by default, gzip is used for this purpose. The tarred gzipped file results in a .tar.gz file type extension.
Q. what do you need to do to get at the data you have just downloaded?
A. In the general case, you will be using Windows of some variant, and should download WinZip, Filzip, or PowerArchiver to access your data. Both of these utilities can access tars, gzips, zips, and several other compression types that Landmap does not use. Once installed, simply double clicking on the data file you have downloaded which will open the file, and display the contents, which you can extract. Note that you should not'drag and drop' the files from the WinZip window to the folder you want to store the data in; if you do this the directory structure will not persist. Use the extract icon on the toolbar instead.
The file you have just extracted may still be gzipped or tarred, again use your zip utility to further extract your data.
If using UNIX you can extract files using 'gunzip filename.gz' and 'tar cvf filaname.tar'. The UNIX man (help) pages will have more information about these utilities. The utilities can be downloaded free of charge from one of GNU's mirror sites (see below).
Q. Where can I download a program which extracts zip files so I can get to my satellite data?
A. You can download zip extracts program from the following sites
www.winzip.com
www.filzip.com
www.7-zip.org/
www.powerarchiver.com/download
