Offhand, the only thing I know about CGI in TNG was that it was considered for use of the production of all visual effects on the show but then some decision was made to go with ILM and modelwork. That the first CGI moment was, I think, the alien space creature in 'Galaxy's Child' and then I think Generations was next for TNG to use it for visuals.
But to be honest, I couldn't tell you how planetscapes were created at that time anyway. I wouldn't have thought models were used for planets. I just assumed some sort of painting effect. But whether it was even then a sort of CGI...................I'm not at all sure.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist