A half century ago I was an expert at drawing 3D images with a T-square and triangle. Architects drew on large sheets of vellum or mylar with sharp pencil leads and precise technical pens. The process of laying out a 3-D drawing started by locating the horizon line. We worked from a 2D plan and would then project from the elevations by manually taking each line to the proper vanishing point. We learned to render one-point perspectives for most interiors and two-point perspectives for exterior views.
Clovis Heimsath in the Early Days
I was fast. But it still could easily take me an entire day to layout the overall perspective and then erase the "hidden" lines and use shading or line-weight to make the image more legible. Frequently, the line drawing felt too diagrammatic. I learned to embellish my 3D perspectives with watercolors or pen and ink to make presentation renderings.
Sometimes a client liked the first 3D picture of our proposed design so much, they would want another from a different point of view. It was faster the second time since we'd be using the same plan. I'd reestablish the horizon line and place new vanishing points. Within a half day I could have a pretty good new picture, having projected all the walls and roofs as I had before. I might not embellish the rendering to the same detail, though. It took a lot of time to render in the stones on the wall, for example. That was quite a lot of fun and made the picture look good, but I might not have the time to do it twice.
The production of 3D renderings evolved a little when published perspective charts became readily available. You could pop a plan onto a perspective chart that had lines going to vanishing points and save the time of constructing the lines by hand. At the end of the layout, of course, the building had to be brought into 3D by blocking in the elevations in perspective. I was good at 3D drawings and I have always felt we must see a building in 3D to understand the scale and ambience of the elements.
In the early 1980s I began to use an early MacIntosh computer. I tracked down a beta version of MacPersective and soon realized that we were at the cusp of a revolution. This primitive program made it possible to layout a building in plan, while it projected up the elevations to make a wire-frame 3D model. I was one of the first in the office to master this technique. I was delighted to do away with the horizon line and vanishing points. Once I construct a building in the program, I could view it from any location.
I contacted the inventor of MacPerspective to encourage him to go further. Soon, he had developed an upgrade to automatically erase the hidden lines! These were just the baby steps, but I knew it would only be a matter of time before the use of computer 3D would be second-nature to anyone involved in design or construction.
We've experienced many benchmarks as we've integrated the electronic perspective into our design process. I was an early user of Sketchup, and I still enjoy using the software's flexibility and intuitive interface. Soon, the office started to explore the benefits of real-time walkthroughs. For a while we were power users of Virtus, an early walkthrough program. Our CAD software at the time allowed us, with some effort, to take our 3D diagrams and make short film clips moving through the images. We have a collection of these presentations like the one featured below. Here's a link to our UTube site HeimsathArch with architectural videos.
We also soon realized that there was still an important place for the watercolor rendering. I continue to render using our computer images as a starting point, then embellishing the images with my artistic hand. Though it is possible today to use highly refined imaging software, making the final presentation by hand can be much more successful.
But the biggest 
change is still unfolding. Our current CAD software actually keeps its data in a 3D model. This makes it possible to access a real-time image of any part of our building design at any time. Though we continue to export fly through video clips, we prefer to take our computer files to meetings so we can move around and through the spaces. It is the closest thing I know for sharing with clients, consultants or anyone else the images we, as architects, have in our imaginations.
You also may enjoy a terrific feature on Clovis and Maryann Heimsath in the January magazine of Texas Architect. Get a link to this feature this in our NEWS.