JOE DEMARCO’S GEOMETRIC PROJECTOR METHOD DESCRIBED

The first requirement for making a perspective projection is an accurate three-view drawing of the airplane (or other object) you wish to draw^a. (If you wish to follow the procedures by making a hands-on drawing of your own, a three-view in the form of a simplified version of the Spirit of St. Louis is provided at in Fig 7.) In addition to the three-view and a suitable drawing surface, the following items are also suggested:

• Good quality 1/10-inch-grid graph, or tracing vellum.
• An accurate ruler (decimal scale recommended.)
• A 30-60 triangle.
• A T-square or similar long, flat straightedge.

The WORKSHEET – The procedures for setting up the worksheet (Fig. 2) and projecting plot points to the picture plane (Fig. 3) are described in the following steps. The worksheet consists of two contiguous areas, the Horizontal Plane and the Profile Plane.

(Click to zoom) Fig. 2 -- All of the essential elements for a perspective projection are identified in this typical worksheet arrangement. (In this illustration, the Azimuth and Elevation viewing angles are set to project a right front 3/4 view of the airplane from below. Also see Fig 4 and Fig. 8.)

In the Horizontal Plane:

1. Lay in the Plan View Line of Sight (PLOS).
2. Intersect PLOS with a vertical that extends into the Profile Plane area. (The intersection
   of these lines is at the plan view Center of Vision (CV)).
3. Place the airplane Plan View on PLOS at the desired Azimuth (Azim) viewing angle^b with its Center of Interest, CI, coincident with CV.

In the Profile Plane:

4. Let a Baseline (BL) – parallel to PLOS – intersect the vertical at CV (seen from the side.)
5. Through CV, lay in the Line of Sight (LOS/CVR) at the desired Elevation (Elev) viewing angle^c.
6. Lay in the Picture Plane^d (PP) perpendicular to LOS.
7. Mark the Eye Position (EP) on LOS at the desired Viewing Distance (Dist) from CV^e. Transfer EP vertically and mark a similar EP on PLOS.

8. Place the airplane Side View^f (and/or Front View) with its CI on BL at a convenient place on either side of the vertical line.

   NOTE: (The Plan View provides LENGTH and WIDTH data. The primary purpose of the Side view is to provide HEIGHT data--the third dimension--thus, it doesn't matter if the airplane points to the left or right. The Side View is usually sufficient for the purpose, but the Front view may be necessary to provide wing dihedral, multiple engines, wheel caster and similar features not clearly discernible in the Side View. If the Front view is required, it may be placed either over the Side view or elsewhere on the Baseline.)

This completes the setup. The worksheet is now ready for the perspective projection; see topic Making the Projection, and Fig. 3.