Loft Bug, view bug

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 From:  Val (GAT)
2688.1 
Hello, I am getting some weird issues with Loft. When I use a cylinder or a circle to Boolean a whole in a surface, and then select the edges of the whole to Loft a surface. I worked around this problem by cutting a cylinder instead of Loft. Also, there were some weird geometry that I deleted around the whole, some sort of tiny polygon edges. I attached the file with only the first problem. "Mesh angle at 5"



Another problem is when zoom close to the surface, one scroll to zoom in is two scrolls to zoom out. I think that its not the zooming out part that changes, but the zoom in. Very annoying at times. Also, for some reason rotation center will change to free when moving close to an object. It switches back to hot point when you zoom out.

Some kind of DirectX issue?:

EDITED: 14 Jun 2009 by GAT

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 From:  Michael Gibson
2688.2 In reply to 2688.1 
Hi Val - re: zooming issue - that kind of a thing will happen if you approach too closely to the target point. When you get to a very small distance away from the target point, when you zoom in further than that you will move the entire target point forward too. Otherwise you would get kind of "stuck" in one place pretty easily if it only every approached the target but never pushed it back.

One thing you may try when you want to zoom in by a finer increment, is to use the Zoom button on the bottom viewport tools instead:



Click and hold down on that button and move the mouse upwards just a bit while still holding down. That will allow you to zoom in with a smaller increment than the scroll wheel. It's hard to provide this kind of fine-tuned control with the scroll wheel since it goes in kind of single click-like increments.

By using the zoom button you can come approach the target more easily without jumping past it.

I'll also take a look at your Loft problem shortly.

- Michael
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 From:  Michael Gibson
2688.3 In reply to 2688.2 
Hi Val - also one other tip for zooming - it can also help if you place the view target point to be snapped on to your particular point of interest that you want to approach.

To do that, use the "Area" button on those view tools - when you place the center point for that area zoom, it will become the viewport's target/pivot point and you can snap it exactly on to a particular point which can make it easier to approach it more closely, especially when you use the zoom button with a more subtle movement amount rather than the scroll wheel.

Also, one last thing - if you are still having problems with approaching a point you can also switch the 3D projection to be a parallel projection rather than a perspective one. To do that go to Options / View / 3D view projection and set that option to "Parallel".

With a parallel projection view zooming in the 3D view will work more like how the Top/Front/Right views work - the zoom is controlled more with an exact scale factor applied to the view rather than moving the eye point around which is what happens when zooming in a perspective view.

Because the parallel view does not move the eye point around, it also won't have that "went past it" type of problem that you were describing.

- Michael
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 From:  Michael Gibson
2688.4 In reply to 2688.1 
Hi Val, some notes on the Loft thing,

> Hello, I am getting some weird issues with Loft. When I use a cylinder
> or a circle to Boolean a whole in a surface, and then select the edges
> of the whole to Loft a surface.

Actually the best way to do this is to make sure your base object is a solid first, before you do the boolean.

When you boolean a solid with a circle as the cutter, it will automatically leave behind the "side walls" of the extrusion of the circle so you don't have to do any other lofting steps after that if you work starting with a solid.

If you are working on a surface, then it will cut the surface and you will have a hole, but like you saw here it will require some extra work to fill in the side parts.

Also you will get a much more complex "side wall" surface if you try to Loft the edges that were produced by a boolean intersection command, since those edges are the result of a surface/surface intersection and will generally be a lot more dense and complex than a simple cylinder surface. So it's best really to avoid doing that process anyway.

Just a quick illustration of the more optimal method - if I start with a solid box here:



Then when I do a boolean difference with the circle as the cutting object, I get this result:



Then there is no additional work to do at all, it's all done because when booleaning a solid, MoI is able to figure out how to combine the volumes of the original shape with the extrusion of the cutting curve, to leave the side walls in place.

When cutting an open surface rather than a solid, it is not really easy for MoI to have as good of an understanding of which regions of the side pieces are supposed to be kept and which are not.

So if you kind of keep your base object tuned up to be a solid you can then take advantage of some of the solid modeling steps to save some steps in situations like this.

Otherwise, if you are working on surfaces only, instead of doing the boolean with the circle and then trying to loft between the open edges, it is generally a better idea to extrude the circle into a cylinder, then trim the cylinder and the main object with one another to make all the pieces which you then join together. That will produce more simple final geometry since the extruded surface is more simple than a loft between 2 possibly heavy edges that were produced by surface/surface intersection.

- Michael

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 From:  Michael Gibson
2688.5 In reply to 2688.1 
Hi Val, finally looking at the Loft issue itself - it seems to be actually functioning pretty normally between curves that are made up of several segments and of a fairly small size like you have there.

By default the Loft is trying to make a result with a lower control point density in it, by doing a refitting process on the input curves. That refitting process can cause the lofted result to sag a small distance away from the original input curves. The sag amount in this case is small enough that you can still successfully join the lofted result with the main object.

If you want to get a more accurate result with no fitting involved at all, you can do that by switching the Profiles option in the Loft command from Profiles: Auto to be Profiles: Exact instead.

The exact method will not do any fitting, but it can result in a heavier surface with a larger number of control points in it, since the lofted surface will kind of inherit the structure of both curves combined together directly.

But like I mentioned in previous messages, I would really recommend making your base shape to be a solid first before doing any of this cutting since then each cut will leave the result as a solid and you won't have any extra filling in to do.

- Michael
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 From:  Val (GAT)
2688.6 
Oh man didn't mean to take up your time this much, that is a lengthy answer. I was not aware of the Exact command affecting alignment of edges during loft, I thought it only affected loft direction. Thank you.
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 From:  Michael Gibson
2688.7 In reply to 2688.6 
Hi Val, no problem!

The navigating part in particular is just a bit hard to explain in too short of an answer without it being cryptic...

Hopefully some of those tips about using Zoom area to get centered on a particular point, and also the zoom button for a more subtle approach slower zoom may help.


> I thought it only affected loft direction.

The direction of a section is actually controlled by clicking on the profile curve in the viewport while in the Loft options stage. A click on a section during that time will reverse it and if it is a closed section there is also a seam grip that will appear which can be dragged to alter the connecting seam between the profiles.

But there is an automatic optimization process that tries to figure out good direction and seam placement for you, which usually does a good job. So most of the time it is not necessary to adjust the directions manually, unless you want to purposely introduce twist.

- Michael
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 From:  Michael Gibson
2688.8 In reply to 2688.6 
Hi Val, also another thing I added in now for the next v2 beta is if you hold down the Ctrl key while using the wheel, it will go in a smaller increment. Also if Ctrl is down it won't do the "slide target point forward" thing that normally happens when you get close to the target point.

That should then be another way to help allow zooming in more closely to a small detail in the perspective 3D view.

But the zooming action in perspective still does move towards the target point, so if you are trying to approach to a specific point it is a good idea to set that point as the target point with Zoom area so that you will step right up towards it instead of possibly going past it.

The other thing you had noticed previously, where sometimes you may get a situation where one click of the wheel forward and then backward does not necessarily take you to the precise same original spot is just a normal consequence of how zooming works in a perspective view - in perspective the zooming is not really an exactly controlled thing, it is accomplished by moving the eye/camera point around. The amount of distance that each wheel click moves is dependent on the current distance from the eye to the target point, it will use a fraction of that distance. But after every move that distance has changed, so a movement outwards will not necessarily use the precise exact same distance as what the previous forward step used. If it always used just a hard coded distance to move forward or backwards, it would provide a kind of forward/backward symmetry but it would have a lot of other problems because it would be even easier yet to zoom right on past some detail that the target point is focused on. By moving by a distance that is a fraction of the current length between the eye and target, it kind of helps make the movement approach the target rather than just fly right past it all the time.

If you switch off perspective in the 3D viewport, then all of this works quite a bit differently, the zooming in a parallel viewport is controlled by changing a scale factor value and not by moving the eye point around in the scene.

- Michael
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 From:  Val (GAT)
2688.9 
Thanks once again, all of your tips are very helpful. I was not aware of how view operation really functions. I will keep an eye out for other things/issues.
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