Sketchup is Inacurrate???

here's one done in rhino then brought into sketchup and segmented.. it looks as if this version has the 5m crosslines perpendicular to the curves whereas yours look to be leaning..

thing is, i can't figure out how someone could calculate where exactly perpendicular to a curve like this is in a polygon app.. have a look at this .skp and see if you can find any sort of method/reasoning to achieve it manually..

bez0ffset.skp

as far as i can gather at this point, the best we could hope for in sketchup along these lines would be some sort of educated guess ?? (actually, i bet it's possible to do it accurately with a segmented modeler but at that point, the app would have enough info to display the true line so why bother segmenting it)

jeff hammond

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here's another example of sketchup acting in an intelligent manner with regards to its arcs..

if you use the arc tangent snap on another arc, it acts appropriately and accurately..
then explode the other arc and you'll see it gives a different result (the correct result for that situation)..

i was a bit surprised to see sketchup handle this properly (it's different than other 'smart' examples i've given because in this case, sketchup is correctly identifying whether pre-existing geometry is an arc or a series of edges (even though the look identical) then reacting accordingly

but it's a good example of how sketchup could also be identifying whether the user has an arc or edges drawn prior to offsetting/followme_ing and reacting correctly..

jeff hammond

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or maybe showing it this way makes it more clear..

the top row consists of the same radius half-circle with the only difference between the three being the number of segments in the arc (2, 6, & 12 segments)

i then drew tangent arcs using the arc tool's tangent snap.. notice all three radii are the same.. (it wasn't paying attention to the half-circle's segments.. only the fact that it was an arc entity that it was connecting to)

the bottom row is a copy of the top row except the half-circle have been exploded into individual segments..

trying the same thing with the tangent snap now considers only the last segment and goes tangent off it..

jgb

Using Bezier curves does create an elegant solution, BUT, NOT for real road design. You do not want a changing curve for a real road, as most drivers would not be able to accurately (and safely) negotiate the curve. That is the reason why road curves are mainly true circular arcs; they are a constant turn angle for the driver. Aside from that, road construction is easier and cheaper.

Take a look again at Pilou's picture of the winding mountain road. All the curves are circular arcs. Using Bezier curves would have made a nicer looking road, but far more difficult to drive on (as if THAT road were easy ).

pilou

Judicious remark !