-> And what about a Marc sized dot in there? :)
I'll have to gain a little weight to be noticed!

The "center" snap does not appears to work on the planets, most probably related to scale...
If I did a bounding box the center would snap though.


Marc

I have made this sort of thing in the past with autocad :)
That is very pertubating to think that you can draw the sun at its real scale!

But there is a little problem when you want to print it at Scale 1/1 on a tracer paper :)

Hi Marc,

> The "center" snap does not appears to work on the
> planets, most probably the related to the scale...

Yup, that's definitely related to the scale - the thing that detects whether a curve is an arc or not doesn't work on such large scaled objects because it uses a pretty tight tolerance to validate that different points on the curve give the same center point as expected with an arc.

But with objects at such a huge scale, a lot of smaller-sized calculation accuracy is lost (that's just how floating point math on the computer works, it's what allows for a wide range of possible numbers to be stored in a fairly small amount of memory), and that makes the center point calculations different enough for the circle to not register as an arc anymore as far as the center osnap code is concerned.

You'll see all kinds of various side effects from losing calculation precision with large numbers like this.

In some cases I've tuned up the calculations to use a tolerance factor that's some relative fraction of the object's overall bounding size, and things that have been adapted to this system instead of only a fixed size tolerance can work better in these cases. I can probably make center object snap tuned up to work in this way so that it would work on these objects, I've made a note for that to try for v3.

- Michael

I'm not able to look at these files at the moment since I'm on Linux. But I have an old AutoCad file named Solar.dwg that you can find if you Google it.

It is the entire solar system drawn to scale. If you zoom window down to the moon then continue to zoom into a little white circle (a crater) you can find a little green spot and zoom into it. It is a drawing of the Apollo 11 lunar lander. You can continue to zoom into the red plaque on the leg of the lander and read the inscription, including the names of the astronauts, the president and the date and a dedication. The letters are 3mm tall.

That's the kind of accuracy fifteen decimal places will get you -- the entire solar system to accurate to 3mm.

Of course if you moved or copied some stuff around everything would be rounded off and who knows where those letters would end up.

Years ago i made a graphic story for the small daughter of a friend that did this kind of thing. It started with a graphic of her cat sitting on the doorstep of her house, and if you zoomed into one of the cat's eyes, there was a map of the world, and eventually you zoomed into the city, then the suburb, then the house, and there was her cat sitting on the doorstep....

And if you zoomed into the other eye...

I did this in generic cadd6, but it struggled with the zoom resolution; I always meant to try it with autocad, which I believe "resets" the zoom, so in fact the zoom level is limitless...?

cheers
rabbit

Interesting Idea!

If I remember in autocad you would have to use a command redraw the view, at a certain point the curves wouldn't be smooth at all.

Marc

If I remember in autocad you would have to use a command redraw the view, at a certain point the curves wouldn't be smooth at all.

___________________________________________________

"Regen" or "Regen All" for regenerate the drawing.

I don't at all know how this stuff works under the hood but I wonder if AutoCad uses a different system of math than more modern programs. They tried for years to keep up with the parametric 3d programs by glomming tools on top of basic ACad but in the end had to write Inventor from scratch and buy Revit, Maya and Mudbox. It is easier now for sure to work in ACad 3d but you still have to move the UCS around to draw at an angle.

Anybody able to explain in layman's terms what changed over the years? Does it have anything to do with floating point math? Or maybe how 3d space is defined?

I'm just curious.

ch

Hi unclecharlie, as far as I know AutoCAD does not use any special system of math and does not actually have unlimited zoom. It's not particularly feasible to have unlimited zoom in any CAD program because there is a fundamental limit to accuracy based on how much memory is devoted to storing a number.

> Anybody able to explain in layman's terms what
> changed over the years?

What change are you talking about? Not much has changed in the basic geometry handling of AutoCAD...

You still have to use the regen command in AutoCAD, at least with AutoCAD 2008 which I just tested with. For example draw a small circle on the screen then zoom in to it, after zooming in you'll see the segmentation in the circle which will go away if you use the Regen command.

That's just how AutoCAD's display system is designed, it sets up a kind of static representation of the wireframe of the model and doesn't try to adapt the density of lines on the fly. Other programs like MoI which don't need a regen command are actually constantly recalculating the set of lines that make up a curve's visual representation at every screen redraw, that's what eliminates the need for a special regen command but if you go back to computers 30 years ago (where AutoCAD has its roots) they were a lot slower than they are now and it was hard to make things do dynamic calculations.

- Michael

"What change are you talking about? Not much has changed in the basic geometry handling of AutoCAD..."

I'm actually asking about the changes that allow other programs to do things like parametrics and dynamic re-assignment of the drawing plane that AutoCad can't do. It just seems to me that they are stuck with some core functionality that they can't really improve on in an efficient manner, so they end up buying newer companies in order to keep up with the competition. I'm guessing that the way the math is handled at the base level is what they are stuck with and if they changed that they would break everything else.

I teach AutoCad, Inventor, Revit and Sketchup at the technical college level. (I got interested in Moi in order to learn about nurbs based modeling in case students start asking about it. Everybody wants to be a car designer!) AutoCad has reached the point where they continue to change the interface year after year without actually improving the efficiency. I wish they would just leave it alone, but that doesn't sell new copies of the software.

Hi unclecharlie,

> I'm actually asking about the changes that allow
> other programs to do things like parametrics and
> dynamic re-assignment of the drawing plane that
> AutoCad can't do.

Well, those changes would most likely be just raw speed increases in the computer hardware.

In general things that are dynamic and more graphically intensive also require more CPU cycles to make them happen, and 30 years ago when personal computer CPUs were much slower than they are now that would have an impact and tend to limit the software design more.


> It just seems to me that they are stuck with some core
> functionality that they can't really improve on in an
> efficient manner, <...>

Yeah, that is a pretty common problem - sometimes older programs become complex over time with layers of stuff built on each other and when things get to a certain size it is a really big job to try and alter various kinds of lower level things. Or I should say it's a really big job to alter such things without causing a large number of bugs from various other parts of the program that assumed that things were structured in one particular way...


> I'm guessing that the way the math is handled at
> the base level is what they are stuck with and if they
> changed that they would break everything else.

I don't have any information about it specifically, but it's not necessarily anything to do specifically with math handling, it's just easy for quite a lot of additional code (including code from other companies as well when you have 3rd party extensions going on as well) to have dependencies on the existing overall design, and trying to change that design would require a ripple effect of changes needed to a lot of other code as well.

- Michael