Join Scott Onstott for an in-depth discussion in this video Visualizing the model, part of AutoCAD: Documenting 3D Models.
- Let's open the Sextant-01 sample file. This is a 3D model of a sextant that I designed based on some images that I was able to find of historical sextants on the net. The sextant is a navigational instrument used by mariners for thousands of years. It's a little bit of an anachronism today with GPS satellites, but the sextant remains a great backup instrument to determine your latitude. I think it's important whenever you're documenting a 3D model, just begin by visualizing it first in your mind.
And that's what we're gonna do in this video. When we open the sample file we're looking at a top view, and it doesn't make a lot of sense. We have to orbit around and take a look at it from different vantage points to assemble this in our minds as a sextant. Use the ViewCube and click on the lower-left corner to switch to an isometric viewpoint. We're getting a better view, but it still looks sort of like a mash, because of the fact that we're looking through all of the objects in Wireframe Mode.
Go up here and change the visual display style to Realistic, and then zoom in. You can use the ViewCube to orbit around into different orientations. Or better yet, hold down the shift key, and drag the mouse wheel to orbit freely. This will give you the best visualization of the objects. So the sextant has a yellow frame here and there's a handle over here on the side that you hold and you look through the lens.
There's a little telescope here that you're looking through. And just for sake of interest let me just explain how the sextant works. Here's a representation of the sun. The sunlight comes down this white line, reflects off this mirror, goes through these sunshades, which are just like sunglasses in reducing the intensity of light. The light bounces off this mirror and goes into the telescope. Notice that only half of the space inside the telescope is filled with that image of the sun.
The other half is looking at their horizon, and that's represented by these waves. And what you do when you're using the sextant, is you bring the sun down so that the center of the sun is right on the horizon. And when you do that, you're rotating this arm around this pivot point in the center of this circular area, and the arm is sliding on this calibrated scale. And when the sun is right on the horizon you can push this green lever to freeze the arm in position.
And then you can read off on the scale what your latitude is. So that's generally how a sextant works, and I thought you might appreciate that, seeing that we're gonna be using this model throughout this project.