Geometric basics
The co-ordinate system
The co-ordinate system is used for the description of point positions on a plain. In clothing construction the plain is comparable to the paper on which the pattern is designed. All points on the plain relate to an agreed source (a starting point). The x and y axis run through this point in a right angle towards one another. Unless otherwise defined, the x axis runs horizontally, the y axis vertically (Picture 1).
X and y co-ordinates of a point
The position of a point is clearly defined by its distance to the x and y axis. The distance to the y axis is the x co-ordinate of the point, the distance to the x axis is the y co-ordinate of the point (see Picture 1).
A minus in front of the x co-ordinate places the point to the left of the y axis. The y co-ordinate is negative if the point lies below the x axis. A point is clearly defined by stating (x,y) (Picture 1).
Picture 2 shows points and some of their respective co-ordinates.
The position of a point can also be defined relative to another point in the construction.
In Picture 3, the new point of reference is point (5.5,2.5). The absolute co-ordinates of the point result from its relative co-ordinates and the co-ordinates of the point of reference.
Polygon
All lines, circle arcs and curves are displayed as polygons in Grafis. A polygon consists of a number of points connected by straight lines (Picture 4). As a rule, the fulcrums of the polygon are not visible.
With the functionmeaure line 
, they can temporarily be made visible as points, if necessary.
The fulcrums of a circle arc have the same distance between one another. The fulcrums of a curve are denser in areas of strong curvature (Picture 5).
For certain construction steps the beginning and end of a line have to be determined. The line receives a direction.
For certain construction processes, it is necessary to define what is the start and the end of a line. The line receives a direction.
Grafis supports the user with the so-called "right principle cursor" which additionally has a direction indicator., not only the objects are determined when clicking the line/curve but also a direction in which the object is to be used.Grafis supports the user with the so-called 'right principle cursor' which also contains a direction indicator.
To illustrate the right principle imagine the line/curve to be clicked as the central reservation of a road. The required direction of travel is communicated to the system by clicking the line. The construction of corners resembles driving on a motorway junction. You are driving along the first line towards the junction and then turn onto the second motorway. The direction of travel is determined by clicking the lines, following the right principle. The stretches of motorway you are driving remain existent, the others are deleted.
Angle definition
Definition of angles is required for rotation transformations, determination of direction in certain curve points or construction of lines. The following rules apply (Picture 6):
- The definition of angles ensues from the positive x axis - if no other reference is present. This agreement is important for definition of points through their distance to the source and their direction.
- A positive rotation angle creates anti-clockwise rotation, a negative angle results in clockwise rotation.