Full Version: Hidden line removal progress

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Hi Marc,

> The rendering and vector curves overlapped is something I have never seen and will be a
> major timesaver for my work.

I was hoping it would be useful for your work!


> When profile lines have less segments (joined curves) it's easier to edit afterward.
> I imagine it must be hard to set a mechanism that works great in all situations though.

Also the tricky part is maintaining accuracy, it's fairly natural for fitting mechanisms to use more points in order to make the fitted result reasonably accurate. I may be able to put in some parameters to control the accuracy level at some point but I'm not quite sure about having that done for this round of work.


> As mentioned, a closed shape for the main silouhette would be great.

Unfortunately I think that's going to be really difficult to achieve, I think the best that I'll be able to do is to have an option to just try and separate out portions of curves that are on the full object silhouette so that you will have something to work with, and if you just want to make an accented border it just having a set of curves in that area may hopefully be enough for that kind of use without it being fully closed.


> It might be interesting to have a special export window, like when exporting polygons.
> It could have a preview and some options for including the rendering or not, lighting options,
> hidden lines, resolution, etc.
>
> Or maybe a 'options' button in the export pdf file dialog window could be handy.

Yeah I haven't gotten to this UI part of it yet. I'm fairly certain that PDF export dialog will get bigger with additional options right on that dialog.

I'm not sure about doing a preview, it would be nice to have but I've got to balance that against how much time it would take to implement it, and I'm not sure if the preview is going to be really particularly useful, like I'm not sure if you'd really be using it as a basis to modify parameters or not as does happen with meshing output.

- Michael

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Hi Marc,

> > """""""""""""""""""Also I was thinking for the background bitmap image to maybe shrink that down by
> > half in width and height to get a downsampled antialiased result with a bit of blending in the border
> > areas and also cutting down file size by a ways.""""""""""""""""""

> I'm not sure I understand what this mean, would it be easy to post examples?

Basically it means whether the background bitmap should be shrunk down by half and kind of blurred somewhat as a side effect of the averaging process during the shrinking.

The sort of good part is that the blurring would give the alpha transparency around the borders of shapes to have some partially translucent spots rather than only having either fully opaque or fully transparent spots with no in between things.

The bad part is that with less resolution the pixels are larger and more noticeable when zoomed in.

Maybe to start with I won't try to do any kind of processing on the background image and just leave it up to you to do any blurring or down sampling if you want that.

- Michael

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Hi Burr,

re: generating hidden lines also in addition to visible lines.

> For me it would be nice to have access to these (as seperate object/sets as mentiond).

I think enough people have mentioned that they will occasionally use these that I'll try to have an option for making them, probably just unchecked by default.

- Michael

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Hi Martin,

> I attached a nice pdf about the two lineweight illustration principle from
> http://purdy.gatech.edu/wp-content/uploads/2012/07/2_line_wt.pdf

Thanks for posting this, this also helps as well. Although in one area it seems to be different than what Matt posted previously, I'll ask some more about that in a separate message in a bit here.


> I don't know if you can control line caps on export but this is also covered.

It is possible for me to control line caps in the PDF file, but trying to do this implies both discovering and maintaining some information about how different categories of lines touch one another. There's a good possibility that trying to figure that out and maintain that information throughout the whole process could add quite a bit of complexity to the whole thing so it's not too likely that I'll attempt that part.


> It doesn't hurt if the hidden lines also get exported as long as they can be easily
> turned on and off like on a seperate layer for example.

I'll see about having an option for this.

- Michael

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Hi Matt & Martin - I'm still a bit confused now about what should be considered an "exterior" or "outer" edge.

I think I see that what I was thinking previously about it being silhouettes doesn't seem to be quite right - they seem to be silhouettes but it looks like only some silhouettes are considered exterior and others aren't.

In order for these to be categorized by MoI I need to be able to make some kind of quantifiable way to categorize these things, I can't rely just on human judgement.

So one thing that has me confused right now is in Matt's insect walking PDF above, this is shown as the exterior edge:





In the one Martin posted, this one is shown as the accented edge:





So to me it seems as though those are 2 different choices, the first one is the longer one on the top surface, while the second one is the short one on the bottom side...



As far as silhouettes go, there are these 2 different silhouettes for that hole:






Right now I don't understand how I should distinguish between these to pick just one of them as the exterior edge.

Thanks,
- Michael

Image Attachments:
exterior_edge1.png  exterior_edge2.png  exterior_edge3.png  exterior_edge4.png 

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Hi Michael

Just using the viewport display as an example ... I would like to be able to export to .pdf with this look.

Now when I export to pdf the hidden lines are solid and as strong as the outer edges.

Thanks for the lighting tip ... that works.

However, the hidden lines only show as dashed when I zoom in as far as my display allows but when I save the normal sized screen display to the clip board and then import it in PhotoShop the hidden lines are simply faint light lines ... so if I had a choice I would like the hidden lines to display as somewhat thicker than they are now and a little more broken.

cheers,

eric

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hi micheal

Yup you've you've understood right. Although in later examples which someone posted, the one with a hole in a plate, strictly speaking the thick thin lifework work would be as my image.

As for naked edges, thats down to the illustrators own interpretation so if it could be in its own style for easy selecting it would be a bonus, otherwise for me it would be enough just to be a thin line.

no to worry with the overall shape. I notice even in isodraw that the overall all fill (they call it a contour) is a bit rough but as it is lying under a thick silhouette lie its usually covered.

Matt

Image Attachments:
Screen Shot 2013-09-30 at 8.09.49 AM.png 

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I am a non-expert, but did a google search for lineweight sketching, and line weight hierarchy. Found 3 rules here:

http://www.sketchmyworld.com/line-weight-importance-in-product-sketching/

Basic Line Weight Usage
1.The thinnest line is used to describe the edges of a product that point towards a viewer and also for the inner lines.
2.Second thickness lines are used for outlines (edges that have air behind them). These are not only contour lines, but can also occur within an object.
3.The thickest lines are used for the baselines – lines that show the interface between a product and a ground plane.


(Seems like there are a whole lot of drafting and architectural standards for line weight and line type. A person could
spend a lot of time on this subject, I guess.)

- Brian

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hi micheal

FYI info I have enclosed 2 screenshots of what Isodraw CADprocess churns out from the 3D models. There are two line thicknesses. have colored the thin one blue zoo you can see easily.
It is by no means a perfect process and i usually have to tidy some parts up but it saves me hours.

Matt

Image Attachments:
Screen Shot 2013-09-30 at 8.29.56 AM.png  Screen Shot 2013-09-30 at 8.30.12 AM.png 

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There is a pretty good explanation for the use of different line widths at the beginning of this pdf:

www.conradiator.com/downloads/pdf/Linethicknesses.pdf

Edit: Added link to paper. Deleted pdf as it is copyrighted.

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This paper looked pretty cool. Maybe some good ideas?

www.gvu.gatech.edu/~jarek/graphics/papers/11DrawingSousa.pdf

- Brian

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The example I've posted previously seems to be taken from page 215 of the book "The Complete Technical Illustrator" by Duff/Maxson and I agree there's some personal choice by the illustrator involved about what lines get thick or thin.

Actually the way I would do it and also the way that seems to be most logical is the attached result by Cinema4Ds Sketch & Toon renderer. This is also similar to mattj example from post 6201.28 but without the "overshoot" which again is a personal style.

Image Attachments:
Sketch-Toon.png 

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Hi eric,

> Just using the viewport display as an example ... I would like to be able to export to .pdf with this look.

Yeah I think that will be possible. Probably by default the hidden lines on PDF export will not be displayed but I'll put in an option for having them and when they are enabled it would make sense to give them a faint dashed line style in the PDF file as well I think.


> Now when I export to pdf the hidden lines are solid and as strong as the outer edges.

Yeah in the current version it's just a total wireframe export with no hidden line determination happening at all, this new stuff I'm working on is a major change in this area.


> However, the hidden lines only show as dashed when I zoom in as far as my display allows
> but when I save the normal sized screen display to the clip board and then import it in PhotoShop
> the hidden lines are simply faint light lines ... so if I had a choice I would like the hidden lines to
> display as somewhat thicker than they are now and a little more broken.

Are you using a keyboard shortcut script to do the transfer to photoshop currently? Can you please post the script that you're using? It's probably possible to adjust the script to increase the line width and that ought to make the dash pattern scale up as well so the spaces between dashes won't be so tiny. Right now the dashes are probably so tiny in comparison to the rest of the image that they blur all together.

- Michael

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Hi Matt, so in this last one that you've posted, this one here (from isodraw):



That's slightly different than what you posted before or what was in Martin's example, because both of those edges are thick in this one, meaning both the red and the blue one I've indicted here:



In your other case you had only one of those edges thickened... With only one thickened the question becomes "which one should it be"... and if it's just an artist's judgement call that's not easy to replicate in computer code.

So I'd probably be shooting for doing the same as Isodraw here and having all silhouette edges get thickened...

Does that make sense? Or is there some specific rule for targeting just one of these 2 possible hole silhouette edges?

- Michael

Image Attachments:
exterior_edge5.png 

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Hi Brian,

> I am a non-expert, but did a google search for lineweight sketching, and
> line weight hierarchy. Found 3 rules here:

Yeah I guess that a "sketch" has its own kind of structure that's somewhat separate from "technical illustration".

In the future I would really like to have more options for sketch like output as well but first I think the focus will be more on the illustration and "shop drawing" type stuff instead.

- Michael

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Hi Martin,

> Actually the way I would do it and also the way that seems to be most logical is the
> attached result by Cinema4Ds Sketch & Toon renderer. This is also similar to mattj example
> from post 6201.28 but without the "overshoot" which again is a personal style.

The style you're showing here is having an accent on the "border against background", having thickness just where the shape touches the background. That's what I'd like to enable by some kind of "outline" option for extracting out those curves.

The other style is not just a difference with "overshoot", it's more about accenting all silhouettes of the object, not just the outermost one. A shape like this should show a bigger difference:



Just the "outline against background" would be like this:



But all silhouettes would be like this:




So I think I want to be able to do both of these kinds of things, like one option to get silhouettes into their own kind of group and another option that will extract out the outer outline only.

Maybe when enabled the outer outline curves would be a duplicated set of curves going over top of the other kinds though.... Not quite sure about that part.

- Michael

Image Attachments:
exterior_edge6.jpg  exterior_edge7.jpg  exterior_edge8.jpg 

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Hi Matt, also I see now that one thing I got confused about comparing your "insect walking" picture against the one Martin posted, was that your one was only a depression and not a full hole all the way through, is that right?

That's why you only had one accented line there, because there was a floor in yours.


Martin, the one that you posted from http://purdy.gatech.edu/wp-content/uploads/2012/07/2_line_wt.pdf - I don't see how I'm going to be able to get that same result with only one of the silhouettes of that through-hole being accented, it's not clear to me which one it would supposed to be so instead I'll probably do both of them.

- Michael

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"""""""""""""I'm not sure about doing a preview, it would be nice to have but I've got to balance that against how much time it would take to implement it"""""""""""""""

I understand, it might be overkill for this feature.

An options button might be interesting instead of adding another dialog.
It would make it a simpler and less intrusive, you change it only if you have to.
Saves could 'stick' between sessions.


Marc

Image Attachments:
Untitled1.png 

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>Martin, the one that you posted from http://purdy.gatech.edu/wp-content/uploads/2012/07/2_line_wt.pdf -
>I don't see how I'm going to be able to get that same result with only one of the silhouettes of that through-hole being accented,
>it's not clear to me which one it would supposed to be so instead I'll probably do both of them.

I regret posting this as it just added confusion. I didn't look carefully. The example shows a subjective way thats difficult or impossible to put into some sort of rule.
I'm fine with your "border against background" method that gives me a rendering like this:

Image Attachments:
border against background.png 

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What will the rule of the internal up arc-circles if this block was on a red table ?
Same rule than an empty backgorund ?
B is satisfying ?





An not only the 2 little arc circles ! As soon as a line has a free touch background all the line must be large!
So a very complex rule!

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