### 1.- Points by coordinates in the dihedral system. Point is located in the first quadrant.

The points are determined by their three Cartesian coordinates, x, y, Z.

The x coordinate corresponds to its deviation, the and its distance, and the z to its elevation.

Let's draw a point A in space, with coordinates 1, 2 and 3.

This point is located in the first quadrant, because its y - z coordinates are positive. View of the dihedral, formed by the horizontal and vertical planes of projection, in perspective.

The earth line is the x axis. we mark the origin of coordinates and to its right this axis will be positive.

We trace the y-axis, on the horizontal plane, passing through the origin of coordinates. Being negative its back.

And, to finish, we draw the z axis on the vertical plane. Being negative its bottom.

On the x axis, we measure the first coordinate, which corresponds to a unit.

From this the second coordinate is drawn, which will be that of the y-axis, measuring in this case two units.

In the term of this coordinate is written the name of the projection, which will be the letter A, with the subscript one.

We finish with the third coordinate, which corresponds to the Z coordinate, drawing three units.

we write the name of this projection, which will be the letter of point A, with the subscript two.

Through these two projections we can place the point in space.

We go down the horizontal projection plane, on the vertical, to go from perspective to the dihedral system.

We observe that the positive y axis coincides with the negative z axis, and the positive z axis also coincides with the negative y axis.