You are absolutely right about using horizontal span. In fact, using the other method (dual view) with nVidia hardware results in significantly slower performance because the rendering is not 100% OpenGL accelerated. Below is one of our tech notes on this issue.
But to address your concern about the distortion, a minor error in how Vizard computes the aspect ratio of multi-display systems has been discovered in the most recent release of Vizard R2 and has been corrected in the upcoming 2.11 release. A temporary work around is to multiply the viewport's aspect ratio by 2.0. In script form, apply an aspect ratio of 2.67 instead of the typical 1.33 of most displays:
Code:
# 50 deg horz. FOV, 2.67 horz-to-vert aspect ratio
viz.fov(50, 2.67)
We apologize for the inconvenience. Below is a fuller discussion of the nVidia issue:
Tech note on nVidia dual view versus horizontal span:
http://www.worldviz.com/support/hardware_faqs.html