No, you need to scale the image after you import it.
The best way to do this is...
1) Know the metric size of your object as depicted in your background images.
2) Create a "bounding box" to those dimensions. In the case of a building, set it up so that the bottom of the box rests on the X axis 0 line... or, if your model will have a "underground foundation" allow for that.
3) Make the bounding box transparent,
or set the viewports to wireframe view, using Main Menu Orth > Wireframe. This is so you can see your viewport graphic without the bounding box blocking the view.
3) Import your graphic into the "front" viewport. Front viewport menu: Orth > Set background image... (navigate to the image).
4) Once the image appears in the front viewport, click in empty space within the viewport to make sure the bounding box is DEselected. Then, quoting from the AC3D manual:
Quote:
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The scale and position of the background image is adjusted by using alt and the cursor keys. Alt and the cursor keys reposition the image, whilst Alt+Shift plus cursor up/down scale the image.
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Scale the background image up or down until its limits match the bounding box, and reposition the graphic so that the building "rests" on the 0 line of the X axis (that is, it's 'on the ground'). Then, repeat this for the side view and top view, if you have background images for those.