Shawn’s Gas Station

The Subject
Original Image

Original Image

Shawn Branstetter of Shortline Modelers asked me if I could use a sketch he had made years ago of an old gas station. In the process I realized that it might be interesting to record the process.

Shawn told me that he had broken his scanner so he used his iPhone to take the photo of his sketch.

Corrected Perspective
Corrected Perspective

Corrected Perspective

The photo that Shawn sent was taken at an angle. To start with I wanted to correct that at least some. One of the tools available in modern graphics programs is the ability to correct perspective. I use Corel PaintShop Pro X5 and in this case the tool is conveniently named – Perspective Correction Tool.

Basically – it is a rectangle that you place over the drawing and then align the 4 corners to a portion of the drawing that would be square if not for perspective. Now .. I have a better starting point.

Sketchup Match Photo – Import
Setting Perspective in SU

Setting Perspective in SU

Now we can start the magic. Sketchup has something called ‘Match Photo’. What you do is import a photo. In this case, the corrected perspective I made above. Now .. when you do this you will see various lines .. two each red and green and one blue. These are used to align the camera in Sketchup so that that virtual camera is positioned as if it had taken the photo. There are ‘handles’ at the end of the lines. You now drag these handles so that these lines .. perspective lines .. match lines on the drawing. I aligned the two green lines along the part of the building runing back . and the red lines along the top and bottom of the building on the front. The blue line with only one handle sets the starting point for the next steps .. the origin. You start everything from that origin – and we can then convert this 2d drawing into 3d. How cool is that?

Tracing the drawing
Tracing Edges

Tracing Edges

Now comes the important part and where you can mess up if you don’t understand some basics. If you do though .. it is fairly easy to get good results.

You SHOULD start at the origin. This is placed usually a corner. The reason is this. When the perspective lines were in Sketchup that defines this world. If you try tracing along a line on the drawing it might seem to you that everything is fine – until you rotate the 3D graphic. When you start at the origin then you are drawing along the perspective lines in THIS world and everything works. This means that I drew a line straight up from the corner. When I next drew horizontal lines along the red-axis or green-axis .. I START that line on this vertical origin line. Other vertical lines such as along the window edges or door edges are drawn from those horizontal lines .. that originated of that first line drawn from the origin. If you think about this it makes sense. Every line is connected back to that origin which Sketchup then can computer to create your 3D mesh.

In this case I have lines along the tops of the walls, vertically at corners, doors, windows and such

Traced

Traced

Removing the photo and you can where we are at this point. This already a 3D mesh. I can rotate the model as needed. The awning extending out from the front of the building is a good example of where this starts to be useful even at this early stage. If you look closely at the drawing above the lines I have for with awning do not match those on the drawing – to which I reply .. oh well. Roofs like this often are not at all straight .. and this also a drawing and not a photo.

I could locate the vertical edges where the awning met the front wall. I could measure how for in from the vertical wall edge that the awning started. With that and switching between 3D and 2D I can interporate the roof.

First Dimensions
First Dimensions

First Dimensions

At this point I can get idea of the size of the building. I know that most doors are around 8ft tall. So .. I scaled the building so the door is 8ft. This shows me that so far .. the building is about 25ft wide and 21ft long.

This is the point that I can let Shawn know about this thread and wait for his comments.

Version 2
color1I got online with Shawn via Skype .. and .. total coolness .. shared my screen. We talked through making some changes.
color2We played around until lunch came rolling around.
Section Plane
sp1a quick section plane through all the windows and doors
sp2With an overhead view, Shawn can work out how he wants the building interior arranged – and figure out where if any, he wants additional doors, windows, chimney etc.

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