# Topological elements in the Shape Maker.

Updated: Sep 30, 2019

**A point in 3d space**.

A point in 3d space is the most common type of point in the system. Such a point is independent of other elements and is the end point of the line or the corner point of the surface. By itself, without being tied to a line, such a point in the system cannot exist and is automatically deleted when all lines coming to this point are deleted. When the position of a point changes, all the lines and surfaces depending on it change the shape according to a given rule.

**A point on a line.**

A point on a line is a special type of point that belongs to a line and changes its position when the shape of a line changes. There are four main options for fixing a point on the line - by one of the coordinates or by the curve parameter. The point on the line allows you to organize the so-called T-junction of surfaces, when several surfaces can be joined at once to the border of one surface. This reduces the total number of surface patches required.

**A point on a surface.**

A point on a surface is defined either by a guiding vector, usually orthogonal to one of their coordinate planes, or by parametric coordinates of the surface. When the surface shape changes, the point changes its coordinates depending on the method of the point definition. As in the case of a point in space, without being tied to a line, such a point in the system cannot exist and is automatically deleted when all lines coming to this point are deleted.

**The point of intersection of the curve and the surface.**

The point of intersection of the curve and the surface can be obtained as a result of the intersection of the point and the surface or as a result of the intersection of the surfaces. The point is always at the intersection of the curve and the surface and is automatically recalculated when the shape of the curve or surface changes.

**The point of intersection of two curves.**

The point of intersection of two curves - can be obtained as a result of the command of intersection of a point and a surface or as a result of the intersection of surfaces if the surfaces intersect with their borders. The point is recalculated when the shape of curves or surfaces changes. Note that the intersection point of the two curves creates fairly tight constraints in the topology and works reliably only in the case of flat curves lying in the same plane. To obtain the intersection point of two spatial curves is almost impossible. The intersection point of two curves can be used to trim lines.

**Line on the surface.**

Line on the surface - the projection of the line on the surface perpendicular to one of the coordinate planes or in the direction specified by the vector. Changes when changing the shape of the surface. Surface lines are used to define surface's trimming contours.

**Line of surfaces intersection.**

The line of intersection of surfaces is the result of the execution of the command of the intersection of surfaces. Intersection lines can also be used to define surface’s trimming contours.

It is important to note that Shape Maker only supports model modification within the existing topology. The modification process is terminated and returns to the last consistent state if any elements cannot be rebuilt. Only the user can manually change the model topology. It is important to understand why the element is not rebuilt and how to correctly change the model. This may be a difficulty at the initial stage of system learning. In this case, it is most convenient to use the properties of the object to check the links of the element with others by direct and reverse links of the element.