PositioNZ GPS Data Service

The PositioNZ Global Positioning System (GPS) data service provides RINEX data from continuously recording GPS receivers located around New Zealand and the Chatham Islands. The data are recorded at 30 second intervals and supplied as RINEX files of either 1 hour or 24 hour duration. This data can be used in post processing of data from roving GPS receivers to accurately locate them.

The hourly data files are usually available within 15 to 20 minutes of the end of the hour. The daily data are usually available within 1 to 2 hours of the end of the Coordinated Universal Time (UTC) day once it has passed a number of quality control measures.

This data can be obtained from the LINZ website or ftp site in a number of ways.

• The simplest method is to use the PositioNZ Downloads page to select the survey marks and the times for which data are required. This will locate the files that are available, notify you of any times for which data is not available, and allow you to download the specific files that you need.
• If you know the name of the RINEX file that you want then you can obtain that file using URL http://www.linz.govt.nz/positionz/rinex/filename, where filename is the name of the RINEX file required. It is useful to know the file naming convention (see below) to retrieve files in this way. This method can be used to obtain both compressed and uncompressed data files.
• You can also browse all the available files and download them from the following site: http://www.linz.govt.nz/ftp/positionz/ . This is more useful for browsing to see what files are available and for bulk downloading of data. Note that all files obtained using this method will be compressed using both the Hatanaka RINEX compression scheme and the Unix compression program. The RINEX files are located in directory structured according to the year, day number of the year, and (for hourly files) the hour of the data, in UTC time. For example, daily files for 6 November 2002 (day 310) are located in a directory 2002/310, and files for the (UTC) hour 09:00 to 10:00 are located in 2002/310/09.

RINEX file naming convention

The RINEX files are named according to a convention as follows:
mmmmddds.yyt
The components of this name are as follows:

mmmm	The lower case geodetic code of the mark, eg "auck" for Auckland. Navigation files use the name "auto".
ddd	The day number of the file starting at 1 on 1 January of each year
s	The session code for the file. This is "0" for the 24 hour data file. The hourly sessions are named " a "to " x " where a is from 00:00 hours to 01:00 hours (UTC time), and x is from 23:00 hours to 24:00 hours.
yy	The last two digits of the year of the file, eg "02" for 2002
t	The type of data in the file, either " o " for observations files, " d " for observation files with the Hatanaka compression scheme applied, or " n " for navigation files.

These files may have Unix compression applied, in which case a ".Z" is added to the filename.

RINEX file compression

Two file compression schemes are used to reduce the storage size of RINEX files.

• Hatanaka compression: Hatanaka RINEX compression was developed by Yuki Hatanaka to reduce the size of RINEX files by taking advantage of the special characteristics of GPS data, and by removing extraneous information. To convert a RINEX file to or from Hatanaka format requires special software. This can be obtained from ftp://terras.gsi.go.jp/software/RNXCMP
• Unix file compression: Unix file compression is a generic compression method supported on all unix systems. This method is often supported by compression software on other platforms (for example WinZip on Microsoft Windows).

For the PositioNZ RINEX files the effect of compression is shown below by listing the typical size of the compressed file as a percentage of the size of the equivalent uncompressed file.

Method	Compression
Hatanaka	35%
Unix	35%
Both	15%