Reference Points and Coordinate Systems
Reference Geometry can also make a Point and a Coordinate System. Like a reference plane or axis, each one is a step in the History tree (Point1, Coordinate System1, and so on) that does not change the part, and each is saved with the part and comes back when you open it again. A point is drawn as a small dot with its name. A coordinate system is drawn as three arrows from its origin: X red, Y green and Z blue.
How to Start It
Click Advanced on the Features tab, then Reference Geometry, then choose Point or Coordinate System.
Step by Step: a Point
- On the Features tab, click Advanced, then Reference Geometry. The panel opens.
- Click Point, then pick how to make it (the list below).
- Pick what the panel asks for, or type the numbers it asks for.
- The new point shows as an orange dot. Press OK to keep it, or Clear to start over.
Ways to Make a Point
- At a point: pick a corner of the part, a sketch point, another reference point, or the Origin button. The new point sits right on it.
- Middle of edge: pick a straight edge of the part or a sketch line. The new point sits halfway along it. An axis runs on for ever and has no middle, so it is refused.
- Center: pick a round edge (a circle or an arc), an arc or a circle of the open sketch, or a face. On a round edge or a sketch arc it is the center of the circle. On a cylinder or a cone face it is the point on its axis level with the middle of the face's area: halfway along a cylinder, and a third of the way up from the wide end of a whole cone. On a flat face it is the middle of the face's area, which is the center of a round flat face.
- On a face: pick a flat face or a plane (or Top plane, Front plane, Right plane). A face puts the point where you clicked it. To place it exactly, also pick a point (a corner, a sketch point or the Origin): it drops square onto the face. Type a Distance to lift the point off the face along the way the face looks; 0 keeps it on the face, and a minus number puts it on the other side.
- Type X Y Z: type how far from the origin the point is along X, Y and Z, in the units the view shows (or type a unit, such as 25 mm). Empty means 0, and a minus number goes the other way.
Step by Step: a Coordinate System
- On the Features tab, click Advanced, then Reference Geometry, then Coordinate System.
- Pick the origin: a corner of the part, a sketch point, a reference point, or the Origin button.
- Pick the X direction: a straight edge, a reference axis, a sketch line, a flat face (X then points the way the face looks), a round face (its axis), or the X axis, Y axis or Z axis buttons.
- If you like, pick a second direction the same way. With Second pick sets Y (the default) it sets Y; with Second pick sets Z it sets Z. It does not have to be exactly square to X: only the part of it that is square to X is used. Leave it out and Y is chosen for you, square to X.
- Tick Flip X or Flip Y (or Flip Z) to turn an axis round. The third axis turns with it, so the axes always stay right handed.
- The arrows show while you pick. Press OK to keep it.
Using Them Afterwards
- A reference point, or the origin of a coordinate system, can be picked wherever Reference Geometry asks for a point: a plane through 3 points, a plane through a line and a point, an axis through two points, the origin of a coordinate system, or another point.
- The arrows of a coordinate system can be picked wherever a line or an axis is asked for in Reference Geometry, such as a plane at an angle.
- The eye beside each one in the History tree shows or hides it. Right-click it for Hide or Show. Hiding does not change the part.
- To delete one, right-click it in the History tree and choose Delete. The window lists any steps built on it first. Planes, axes, points or coordinate systems that were made by picking it are frozen where they are, so they stay; the window names them, even after a rename.
Good to Know
- A point or a coordinate system is frozen where it was made. It does not follow later changes to the faces or edges it came from. To move it, delete it and make it again.
- A point or an origin more than a kilometre from the part origin is refused.
- A second direction that runs along X is refused, because it cannot set Y or Z. Pick one that crosses X, or leave it out.
- A face that is curved but not round (a spline face) has no one direction, so it is refused as a direction.
- Measure and the STL and STEP downloads still use the part's own origin, not a coordinate system you made. A coordinate system is a guide you can see, pick and keep with the part.
Problems
- OK stays grey: the panel text says what is still missing, or why the picks do not work together. For a coordinate system you need at least the origin and the X direction.
- The arrows point the wrong way: tick Flip X or Flip Y before pressing OK. After OK, delete it and make it again.
- My point is not where I clicked on a face: with On a face, pick a point as well to place it exactly. A click on a face lands on the drawn surface, which is exact for a flat face.