Chris Columbus, who directed the first two Harry Potter films and produced a third (and incidentally was greatly responsible for how well the film franchise took off) is now directing Percy Jackson’s “The Lightning Thief”, a story about real life and Greek mythology. He spoke with AMC TV on how directing HP actually prepared him for his current film:
We had the eyes of the world on us when we were doing the Harry Potter films. The prospect of casting the kids was daunting, and I felt the fans of the books were more like, “You can’t change this, you can’t change that.” But by the second film and the third film, I felt like we had earned some freedom. So when we got to this film, I decided that the book stands alone and that the film stands alone, as well. We took the best bits of the book, and I added some stuff, and that’s how it came to be.
You can read the rest of the interview here. He did mention that he gets ticked off when people say that the Lightning Thief is just a Harry Potter ripoff, since he believes that while there might be some basic similarities (orphan, quest to find something) that those are similar elements in MANY books, and the Lightning Thief is unique because of its take on Greek myths.