Warthur
In between their early space rock albums and the hard prog direction they took on In Absentia, Porcupine Tree put out a brace of albums in what I call their "indie-prog" styles - a mashup of their early spacey style with influences from then-current British indie rock. Marillion were plumbing similar territory at the time with the run of albums beginning with Brave - indeed, Steven Wilson would lend a hand on the marillion.com album, which perhaps represents the closest the two groups ever came to each other sonically - but Marillion and Porcupine Tree took somewhat different approaches and took different lessons from UK indie rock, in part because they were coming from different directions in the first place (what worked to evolve Marillion's neo-prog sound wouldn't necessarily have been right for developing Porcupine Tree's space rock, after all).
Stupid Dream, Lightbulb Sun, and the (remarkably good) odds and sods collection Recordings are the studio fruits of this era of Porcuoine Tree's history - but if you want a live taste of this sound, then you want to check out Warszawa, which captures an April 2001 performance with the band in fine form. Selections from Stupid Dream and Lightbulb Sun dominate the track list for the most part, though Voyage 34 and Signify get a look in towards the end.
Perhaps more significantly, there's a slightly heavier edge to the performances here than we got on the studio renditions of many of these tracks - not as heavy as In Absentia, but we are less than a year away from them entering the studio to put that career-transforming album together, and you could certainly see this as a missing link between the "indie prog" era and the heavy prog stylings that would follow, albeit one leaning more towards the former period than the latter. The end result is steeped enough in the late 1990s sound of Porcupine Tree to be interesting to those who enjoy it, but is just different enough that it feels like a missing piece of that era slotting into place - and you could argue that providing a different slant on a band's work is the best thing a live album can offer over its studio predecessors.