The volume of the liquid in the glass is approximately 0.5*glassheight*radius*3.141592653589793238462643383279502884197169399375105820974944592307816406286208998628034825342117067982148^2
Also I have never heard anyone say that a glass is half-empty other than in the situation that this question is asked. So I don't see how the assumption that saying one or the other makes it more likely to be an optimist or a pessimist is justified other than the fact that when asked the specific question wether the glass is half-full or half-empty, people will more likely answer based on the nature of the question and the suggestive description that your answer entails in reference to this specific question, but when asked in normal situations the volume of a liquid inside a container in proportion to the maximum capacity of the container when it is at 50% capacity in a way that does not present two choices people would most likely choose to say that it is half-full because it is the most common thing to say.