Accessing a GalleryPhotoItem entity in Sitemap-like module

I'm hacking the Google Sitemap module to create a new module which generates a datafeed to export images into a 3rd party website.

I've been away from Gallery for a while so am a bit rusty with my coding.

Using the Sitemap module filenames & variables for reference, in Sitemap.inc how do I go about accessing the information inside an entity of type GalleryPhotoItem?

If I do a var_dump($entity) I can see all the IPTC info in there (like Summary, Description, Keywords), but I'm totally failing to work out how to display these elements.
eg. $entity['summary'] doesn't work... what should I be using to refer to the summary element within $entity?

Thanks in advance for any pointers.

Cheers,
David Osborne

Gallery version = 2.1.1 core 1.1.0.1
PHP version = 5.2.0 apache2handler
Webserver = Apache/2.0.59 (Win32) PHP/5.2.0
Database = mysql 5.0.27-community-nt, lock.system=flock
Toolkits = Exif, Gd
Acceleration = none, none
Operating system = Windows NT ACER-0BCB4DEC3A 5.1 build 2600
Default theme = carbon
Locale = en_GB
Browser = Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.8.1.1) Gecko/20061204 Firefox/2.0.0.1