# Normal projection

The normal projection or three-panel projection and in Austria the cross plan is a method for the graphic representation of a spatial object in different planes views .

## use

The drawings of the normal projection are often used in architecture and construction . Presentation drawings are primarily used to represent a concept or draft . Floor plans, sections and views, on the other hand, are measurable drawings. These " construction drawings " are used by the planners to precisely define the dimensions of a building . The executors can use these drawings to implement the structure.

Even with technical drawings , for example in mechanical engineering , the drawings of the normal projection are the most important form of representation and essential for planning and execution.

## Views

Projection symbols according to DIN 6
left: European representation
right: American representation

There are two sides for each of the three orthogonal projection surfaces and consequently six views. There are two systems for arranging the views on paper:

• Projection method 1, also called European representation or First Angle Projection and marked with FR (for French, see also diagram on the right) and
• Projection method 3, also known as American representation or Third Angle Projection (code US), which, however, is also predominant in Australia in addition to the USA.

The symbols shown on the left enable the selected method to be identified using a cut-off cone and the trapezoid as a front view. The unfolding of the projection cube illustrates the underlying logic.

Three of the projections serve as the main view for the three-panel projection. When choosing the front view, the most informative side has priority. Additional views can be added for objects that are difficult to understand. Sometimes one of the three views is dispensed with and a two- panel projection is obtained .

designation old name Position by projection method 1 Position by projection method 3
Front view Elevation center center
Left side view Side tear or cross tear right of center far left
Top or top view Layout below above
Rear view rightmost rightmost
Right side view far left right of center
bottom view above below

## Explanation

From a geometrical point of view, each point of the object is initially described in a spatial coordinate system as P (x | y | z). Then one of the coordinates is set to a fixed value (e.g. to zero) in order to enable a flat display. This corresponds to a projection in one of the ground planes.

Assignment:
view Coordinates level
Front view = P (0 | y | z) = yz plane
Top view = P (x | y | 0) = xy plane
Side view = P (x | 0 | z) = xz plane

A building (picture below left) is to be shown in three-panel projection. Its corner points are projected into the ground planes and connected to one another again (bottom center). Hidden edges are shown in dashed lines.

The three projections are now drawn in one plane by cutting open the spatial arrangement of the three planes along the x-axis and folding it into the yz plane. The x-axis then appears twice in the drawing.

## Excellent straights and planes

Three main straights

A main straight line is a straight line that lies parallel to one of the image planes . Main lines are always undistorted in the corresponding image plane, so their spatial length can be read off directly in the image plane. A projecting straight line is a straight line that lies parallel to the direction of projection. Projecting straight lines are mapped as points in the corresponding image plane, so their length cannot be reconstructed from their image.

A main plane is a plane that is parallel to an image plane. Main levels are always undistorted in the corresponding image level. A projecting plane is a plane that is parallel to the direction of projection. Projecting planes are shown as straight lines in the corresponding image plane.

Depending on whether the image plane is the floor plan, the elevation or the cross plan, one speaks of first, second and third main straight line or planes or of first, second and third projecting straight lines or planes.

## literature

• DIN 6
• Part 1 (outdated, replaced by DIN ISO 5456-2)
• Part 2 (outdated, replaced by DIN ISO 128-30)
• ISO 5456 Technical Drawings - Projection Methods
• Part 1: Overview
• Part 2: Orthogonal representations
• ISO 128-30 Technical Drawings - General principles of representation
• Part 30: Basic rules for views
• Part 34: views in drawings of mechanical engineering