===== Orbit Files =====

ROI_PAC is compatible with either ODR or PRC orbits.



==== ODR Orbit Files ====

From the [[http://www.deos.tudelft.nl/ers/precorbs/|Precise Orbit Determination]] web-page, click the "Orbits" link under the content heading.   Choose the link for "precise orbits" for the appropriate satellite and follow the download instructions for ODR files **and the arclist**.  Remember to also download the program [[http://www.deos.tudelft.nl/ers/precorbs/tools/|getorb]] and install it on your system.  

:!:The ''getorb'' executable must be located in the ''INT_BIN'' directory with the other ROI_PAC executables.

==== PRC Orbit Files ====

A password is required to download PRC orbits from ESA's website.
The file name for PRC orbits can be interpreted as follows:

PPP_yymmdd_no_revi.Z

|PPP|PRC|
|yymmdd|start date of the orbit: year (yy), month (mm), day (dd)|
|no|absolute orbit number (revolutions since launch) at orbit begin|
|revi|revision id|

Retrieve the orbit file with the date and orbit number that most closely __precedes__ the date and orbit of the given SAR scene.  After downloading the necessary files, update the list of orbit files by running arclist_PRC.pl in the same directory.