Lidar is great for distance representations, but requires a highly consistent and exact timing source. Dual optical inputs allow us to approximate the same data through other methods that don't require nearly as exact timing.
Just a small FYI:
If you are doing time-of-flight measurement, then yes. But many (not all) LIDARs out there don't do time-of-flight, because to get the resolution wanted or needed, you need to have an oscillator (and sensors for the return pulse) capable of many, many gigahertz (it can get absurd quickly if you want anything below a resolution of around 10 CMs). This isn't easy or cheap (the oscillator actually is fairly easy and cheap - it's the return sensor that needs a very fast rise time that is expensive and difficult, though such devices do exist - some all solid-state, like flash LIDAR).
What many LIDAR sensors use (not sure about Velodyne) is actually using a kind of "doppler shift" of a laser modulated with a carrier wave. It still needs a high-speed multi-gigahertz oscillator to resolve small changes in distance, but everything else is fairly off-the-shelf and nothing real special. One downside of the method is that there is a discrepancy at farthest vs minimal distance measured due to ambiguity when comparing the received modulated beam to the outgoing modulated beam; you can't tell at such a point what the distance is (because both distances look the same).
But sensors like Velodyne, SICK and I think Hokuyo are pulsed and measure the actual time it takes for the pulse to travel from the emitter to the target and back to the detector.
Units like this:
https://www.amazon.com/Bosch-GLM-35-Measure-120-Feet/dp/B00V...
that go for $75 (or less) do this. They're super accurate, the only downside is that it takes a second to cycle through all the necessary frequencies.
I winder, if we started heavily colonizing Mars 100 years from today, would we bother to build roads?
At first people would anyway live by whatever resource they were using. If a deposit ran out they might choose to build a haul road over moving their entire settlement.
Cue action music.
It's a sucky situation, but it makes for an awesome video game!