There are sooo many ways to do a transition on string instruments.
One issue with portamento is:
Usually a string player doesn't slide all the way from one note to another.
E.g. when playing an octave, the player doesn't always slide from c3 - c4.
Instead, he places the finger on the next string on e.g. g3 (the 5th) and slides from there to c4 (the octave.)
So, the audible transition is only from g3 - c4 (a 4th).
Thats why I introduced the "offset" fader for the portamento transitions in all my orchestral libraries.
The original recording of the portamento transition is a complete slide from one note to the other.
(Every interval up to 1 octave up and down, with 2 dynamic layer))
The offset fader lets you cut the transition, so that you only hear a 4th, a subtle grace note, or any interval you like.
With the Combination of "speed" and "offset" fader, you are able to create a vast amount of portamento variations.
With perfect control over length and tuning with only 2 MIDI CCs.
Here is a tutorial video about Legato in the Chris Hein - Ensemble Strings.
The Portamento section starts at 1:40
The Glide-Mode offers another method to create smooth transitions, but thats another story.
Chris Hein