Evolution of a drawing Idea ...

And some "scaraboti"

The second stage of making the final painting were the more refined drawings, and the renowned scaraboti, where with high detail Canaletto was recording scenes that would later compose part of the paintings he was planning to make.

The use of a Camera Obscura for a faster and more proficient recording of details could be possibly found here, but surely not done with the Box-Type Camera Obscura which can be found at the Museo Correr:

 

but more likely with a Tent-Type Camera Obscura that was available at the time, as we can see in this image:

Very simply put: the Box-Type Camera Obscura flips left/right the image making the reproduction of an architectural subject a very complex process, as we see here:

Let's never forget that painting in Canaletto's case (as in most of the painters of his time) was basically business, and "art products" had to be as commercial as needed.

Canaletto was painting his views because tourists from all over Europe loved them and bought them to take home as a pleasant souvenir to put in their best room.

And, since the most ancient times, the potential customers willing to pay for Art have been:
- The State
- The Roman Church
- Rich Tourists visiting Italy (the Grand Tour), or
- Rich Merchants who wanted to embellish their homes with astounding paintings, or rich customers from Venice too, where ART was so appreciated and cherished in Canaletto's time (and still is!) by those who had money to buy it.