How to draw this street lantern?

As some regular forum readers will know, I’ve been helping Andrew (@Quadhurst) drawing UK street furniture from telegraph poles, through signposts, to street lights from the mid-20th century, for a planned book.

We’ve both got stuck in how to draw the canopy for this SO50 street light.

First, what should the top look like? We have two photos, and front and end profile drawings, but can’t quite make sense of the shape of the top.




We only need to draw the exterior of the lantern, not the interior detail. But we can’t really work out the shape of the upper part of the lantern top cover.

This was the first UK street lantern made of plastic - a perspex bowl, and moulded plastic (polycarbonate?) top.

I attach where we’ve got to in trying to model it. Not very good for the top in particular.


SO50 31 Dec.skp (3.2 MB)

Tried FredoCorner to round the near top curved edge of the drawn part of the top canopy (highlighted in the image below., and it refuses to round it. Tried both ‘full size’ and scaled up x100.

Any suggestions, please, for how to progress this drawing to represent the lantern in 3D in Sketchup?

Andrew and I are both using SU 2021.1.331 on Mac OS Monterey, in case that makes any difference.

Too bad you don’t have a plan view of the thing.

It shouldn’t be too terribly hard.

I’d be working as if inches were meters.

Yeah, more photos and drawings would be very helpful. The ones you shared don’t look entirely consistent to me. Perhaps there were variations?

There doesn’t seem to be one available. It would certainly help.

Scaling up to metres for inches is only x39.37, but I think it’s something I’m not understanding in FredoCorner that’s stopping it working.

Here’s just the half-top component (full size before any scaling):
Half-top.skp (27.6 KB)

Even scaled up x100, whatever offset value ‘x’ I put in FredoCorner for the rounding radius, it says “Offset (x) is probably too large; consider reducing it.”

I want it to be about 1/2" radius ‘full size’ so I started with offset 50 in x100 scale. But even reducing that to 1 (=0.01" full size) still says it’s too large.

Fredo corner does not like places where a face tapers off to a point, such as at the ends of your top. These will trigger that error regardless of the offset you choose.

One possible fix is to intentionally break the curve short of the corners. round the remainder, and then use curviloft to generate the tapered part. Or sometimes you can copy the curve and faces from the component, paste in place outside them, and extend the faces to get rid of the point. Do the round on the extended faces and then use cutters to trim them down to the real shape. Which is best depends on how the actual roundover would terminate.

That’s very helpful, Steve. Thanks. I thought it was probably my limited understanding of FredoCorner that was causing us trouble.

I guess then that we could create a face on the bottom of the half-canopy, push pull it downwards to extend the front face, then round that.

Like this maybe…? (Trying it now).

With some difficulty:
This WON’T work (error and FredoCorner bug report)


But if I add an arc at the left hand end, it will work

But needs a bit of clean up afterwards.


… to get this:

Needed quite a lot of clean up, and an untidy result (not really visible unless I turn on hidden geometry!
Half-top.skp (39.6 KB)

Partial solution, then.

Is there a very different way of modelling it?

A quick sketch, using quads

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That’s looking like a good and different way to do it. Quad-face tools extension?

I’ve heard of that, but very rarely used it.

How do you start?

QuadFace Tools, Vertex Tools, SUbD

Something like this for start
crc-08a

crc-08b

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