That surface can also be extended into a plane, just as we did before, and this time I’ll make that plane light green in color: The simplest one to consider is the plane formed by the surface of stick ‘a’ which is parallel to the surface we already played around with. Today we are going to do pretty much the exact same procedure, this time with another plane.
We then noted how that plane meets the floor and forms a line emanating from the foot of the stick, and with a few magic tricks we produced the following lines on the elevation view of stick ‘b’, showing where the plane from stick ‘a’ intersects it:
That’s how I spaced the lines on the elevation view of the stick, not by using the arcs on SketchUp.Īlright, on with the fun – in the last blog entry in this series we formed a large plane off of one of the surfaces of stick ‘a’, like this:
The distance therefore of the bottom line of the stick (in the elevation view) from the top line of the stick is 28.2842712474619… and the line in the middle is 1/2 of that, or 14.142135623731… roughly. The diagonal of that square is √2 times longer, that is 20√2, which equals 28.2842712474619… or thereabouts. The cross sections of the sticks, which are square, each measure 20 cm on a side. The line’s position is determined not by the arc, which I know to be wrong, but by using a little math. In the above picture it almost looks like the facet arris of the arc actually does meet the line a little lower down from where the arrow points, however if you zoom right in you will see it does not in fact intersect: Now I’ll zoom right in on that arrow, and you can see that the faceted arc does not exactly meet the line: Here, I’ll show you what I mean – in this next picture, I have placed a large arrow pointing to the intersection of an arc and the line which it is supposed to delineate: I figured out the positions of the lines using a little bit of math. The arcs on my drawing are in fact only representational, and the lines that purport to connect to them, actually do no exactly connect to them. Readers who are following along with SketchUp, and who are unfamiliar with its peccadilloes in terms of arcs and circles may run into little errors when trying to connect to arcs. On this charpente problem drawing I am presenting in this series, while I am using SketchUp, I am not presuming that the reader is also using it – in fact I am presenting the material in such a way that the reader with pencil, straightedge, compass and rule can accomplish the drawings.
One can download plug-ins to deal with this, like True Tangent, but in the end, it really is simpler and easier to draw an arc with an old-fashioned drawing compass than SU. One can specify that either the circle or the arc tool have more facets, up to 1000 facets I think, but then it is still hard to know where the tangent point of the circle is located. If one is, on the other hand, connecting to a facet more closely to the midpoint of a facet, then the point is further in than where it ought to be. If, at the tangent point to the arc, there happens to be a facet arris, then the point is slightly further out than where it ought to be. Either way, SU is representing that circle as a series of facets. In SU, there are two ways to draw a circular line – either one uses the ‘arc’ tool or one uses the circle tool and then chops the circle up into the required arc portion required. It’s frankly one of the shortcomings of the drawing program, and has given me my share of hair-pulling moments of frustration at times. Well, don’t worry about that, as it is only going to get worse from here, and the truth, er, is plane to see.Ī couple of readers have commented about having problems rendering or using the arcs I show in the drawing – welcome my friends to SketchUp, and the problem it has with representing curves and attaching lines to curves. After the previous post in this series, the reader may have begun to notice the rapidly multiplying profusion of lines.