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Hi.

I cant understand what is the purpose of putting "a development required because ..." in the following pargraph, what does it refer to ?

"In 1986, Disney Theme Parks and Universal Studios began to use 3D films to impress audiences in special venues, Captain Eo (Francis Ford Coppola, 1986) starring Michael Jackson, being a very notable example. In the same year, the National Film Board of Canada production Transitions (Colin Low), created for Expo 86 in Vancouver, was the first IMAX presentation using polarized glasses. "Echos of the Sun" (Roman Kroitor, 1990) was the first IMAX film to be presented using alternate-eye shutterglass technology, a development required because the dome screen precluded the use of polarized technology."
Comments  
The "development" it refers to is "alternate-eye shutterglass technology," and the statement is that this development was necessary due to the fact that the dome shape of the screen in IMAX theaters was such that the polarized technology (which I assume would normally be used to get the 3-D effect) could not be used or would not work.
Thanks.