Antique Gas & Steam Engine Museum
This is in response to a question asked in the comments
Hey Matt, good question, what you see there is not exactly a grid, because that would not be very helpful for outdoor sketching(while this was done from a photo I was using the same approach I use for sketching "from life") I do not use vanishing points very often in freehand sketches, instead what you are seeing here is what I call squared measurement. Essentially I find an area that is perfectly square (seen in red in the new image on my blog) and then I use this to judge any further measurements and or perspective angles angles and slopes. In blue you see the horizon line which helps me judge point of view and perspective (above the horizon looking up, below looking down) One last note, with something this mechanical I will typically look for a major and minor axis to help me in establishing a crude perspective grid, seen here in green.