I did this initial study freehand, without a ruler and by eye. It was a rainy grey afternoon so that must have blurred the view a bit and there wasn't so much light and dark contrast. I chose the view from my back bedroom window because the weather was against me going out and I found a focus in the next door pergola which covers a fish pond. It is a strong feature that I thought would help me in judging the angles of everything else. That and the horizonals in the pergolas 'legs' and the top and side of the garage in the very foreground.
I then had another go, weather was similar, and this time I established my eyeline was somewhere around the lower part of the window featured in the house in the distance and my vanishing points to the right and left were off the page. I don't think I did too badly by eye the first time but the second attempt looks more accurate.
