Most amateur astronomers have never had the opportunity to use a 3D Viewer, so the concept may take a bit of getting used to. Going through the learning curve is well worth the effort though, because once you become skilled at creating 3D images, you will be able to display and print your favorite lunar features in a way that has never before been possible for lunar observers.
IMPORTANT: The 3D Viewer utilizes extensive amounts of radar elevation data to create true 3D imagery. The computational complexity of this function requires considerable computer resources. Depending upon your system resources, it may take a while to get your results. Attempting to use the 3D Viewer on a computer with a severe lack of system resources may overtax and crash the application.
Click to activate the 3D Viewer. The viewer is designed to display the topography of selected portions of the lunar surface in 3D. At activation, several viewing parameters are initialized, and the portion of the lunar surface that is displayed in the map view is also displayed by the 3D Viewer.
The 3D Viewer allows users to independently control the map viewing parameters. By using the controls, it is possible to alter the 3D view in such a way that correspondence with the original map view is lost. Each time the 3D Button (or related menu item) is clicked, the viewing parameters are reset, and correspondence with the primary map is restored.
When the 3D Viewer is first activated, the standard resolution window is the default display. For users with moderate speed computer systems, this is the preferred setting, since it requires the least amount of system resources, and produces results more quickly.
If you own a high speed, computer system, you may prefer working with the high resolution display. At high resolution, the size of the 3D display window is doubled, as is the amount of detail visible in the 3D imagery. To switch to the high resolution display, click the View Menu then click High Resolution. A check mark will appear, and the display window will increase in size. Clicking again, removes the check mark and returns the display to standard resolution.
The 3D Viewer utilizes several viewing parameters that directly affect the appearance of the lunar surface being displayed. These parameters are introduced and defined below. There are five distinct viewing parameters, as follows:
· Point-of-View the line of sight from the observer's eye to a point on the lunar surface. That point is always centered in the 3D Viewer window directly below the position of the user.
· Magnification the visual effect due to the distance (along the line of sight) of the observer to the surface of the moon. At the minimum magnification, the greatest possible surface area that can be seen at once a hemisphere is displayed in the 3D Viewer window.
Each time the 3D Button (or menu item) on the map displays tool bar is clicked, the point-of-view, magnification, and orientation are set, so that the 3D Viewer displays roughly the same portion of the lunar surface that is displayed in the map view. (The 3D Viewer always starts out with North Up, regardless of the setting used on the primary map.) On the first click only, the relief exaggeration is set to a default value that is pleasing to the eye, and the visual appearance is set to wire mesh. If 3D Viewer controls are used to change either the relief exaggeration or the visual appearance, these will not be reset on the next click.
In the following example, note the difference in the appearance of Clavius as seen on the primary map, and in the 3D Viewer window. The reason for the difference is that the primary map is showing Clavius as seen from earth (at high magnification), while the 3D Viewer is showing Clavius as seen from directly overhead.
As a result of the proximity of Clavius to the southern limb, the primary map is displaying the crater at a highly oblique angle. You will find that as you zoom in on features that are further from the center of the primary map, the differences between the two views will become increasingly more pronounced.
If you zoom in on a region far from the center (without first changing the point-of-view, so you are directly over the center of the region of interest), line of sight creates an oblique angle with the surface. If the 3D Button (or menu item) is then clicked, this same region will be repositioned in the 3D Viewer, but the point-of-view of the observer will move directly over the center of the region.
If the 3D Viewer Tool Bar Controls are used to change the point-of-view and/or magnification, the correspondence, which exists initially, between the primary map view and 3D view is lost. In other words, the primary map view does not automatically adjust to changes you make in the 3D Viewer. To maintain proper correspondence at all times, change the point-of-view and/or magnification on the map view, and update the 3D Viewer by clicking the 3D Button on the main Tool Bar.
The wire mesh appearance is the default because it can be rendered much faster than the realistic appearance. If you plan to modify any of the other viewing parameters in steps, it is much more efficient to do it with the wire mesh view, and then switch to the realistic appearance at completion. Switch back to the wire mesh view again before making another series of adjustments. You may want to follow this procedure whether making adjustments via the 3D Viewer controls or the map view, unless you have a very powerful computer.
It is often virtually impossible to recognize a region when using the wire mesh appearance, if that region is seen from directly overhead, and is sufficiently small, so that lunar curvature is negligible. That is because there is no appreciable shading, and there are no visual clues. Under these circumstances, the realistic view makes it possible to identify your location. The following overhead views of the Copernicus Region, in both wire mesh and realistic view, illustrates this point.
As you can see, the realistic appearance provides sufficient visual clues so you can identify the region being displayed, and generally provides a sense of topographic relief, regardless of the orientation.
As you view topographic features at an increasingly oblique angle, they become increasingly easier to recognize in wire mesh mode due to the improved shading conditions. To illustrate this point, the Copernicus Region is displayed once again, in both wire mesh mode and realistic mode, but at a far more oblique viewing angle.
There may occasionally be situations where the wire mesh appearance shows the relief more clearly than the realistic appearance.
There are two ways to see topographic features in true relief. When using high magnifications to view small regions, it is appropriate to use orientation controls to make the line of sight oblique. At low magnifications, with the line of sight directly overhead, topographic features that are increasingly far from the line of sight are seen at increasingly oblique angles, due to the curvature of the lunar surface.
When an entire hemisphere is visible in wire mesh mode, only the most extreme topography, such as tall mountains and deep craters and valleys, near the edges of the hemisphere, will be seen in relief. To understand this, keep in mind that the height of even the tallest mountains is still hundreds of times smaller than the horizontal distance across a lunar hemisphere.
As you can see in the following examples, it is far more difficult to recognize what you are looking at if the orientation controls are used at low magnification. As the viewing angle becomes increasingly more oblique, more of the curved surface moves below the horizon. In wire mesh mode, that portion will be seen through the foreground mesh, and will be completely shaded, (because it is totally hidden from the light source behind the observer). Since the shading is the same color as the foreground mesh, it obscures any foreground relief.
To avoid confusion, follow these guidelines:
1. First view an entire hemisphere without adjusting the orientation from the overhead position.
2. As the magnification is increased, you can make the line of sight increasingly more oblique.
3. If the image becomes confusing, decrease the obliquity, or switch to the realistic appearance.
The 3D Viewer provides the user with controls for all viewing parameters. They are collected into menus and button groups according to function. In addition, an integrated control panel (discussed later), can be used to provide finer control.
The observer's point-of-view can be modified by clicking on any of four items under the Point-of-View Menu Rotate North, Rotate South, Rotate East and Rotate West, or any of these four corresponding toolbar buttons. .
Each click on a menu item or corresponding button moves the point-of-view along the curvature of the sphere of the moon, in the indicated direction. With each click, the moon is rotated by 25% of the angular distance across the portion of the surface that is visible in the window.
For example, if an entire hemisphere is on display, the angular distance across the surface is 180 degrees. A single click on any menu item or button will shift the point-of-view 45 degrees in the indicated direction. If the magnification is such that the angular distance across the visible surface is say, 20 degrees, then a single click will shift the point-of-view by 5 degrees, and so on.
Whenever a Point-of-View toolbar button is used, your point-of-view moves to a point directly above the feature that is centered in the 3D Viewer window, just as if you were looking down on that feature from an orbiting spacecraft.
The magnification can also be modified by clicking Zoom-In or Zoom-Out, under the Magnification Menu, or by using the two corresponding toolbar buttons. . Each click on the Zoom-In Menu Item or corresponding button, (the button with the arrows pointing inward), increases the magnification by a factor of two. Each click on the Zoom-Out Menu Item or corresponding button, (the button with the arrows pointing outward), decreases the magnification by a factor of two.
When an entire hemisphere is displayed in the window, the magnification is at its minimum value. In this situation, clicking the Zoom-Out Menu Item or corresponding button, will have no effect.
Using the orientation controls is when the fun really begins. The 3D map orientation can be modified by clicking on any of the four items under the Orientation Menu, or by clicking on the Rotate-Up, Rotate-Down, Rotate-Left or Rotate-Right toolbar buttons.
Each click on a menu item or corresponding button rotates the surface 10 degrees about its center, in the indicated direction. (Alternatively, one can imagine that the line of sight is rotating 10 degrees in the opposite direction.)
The phrase Rotate Up means a rotation of the surface about a horizontal line through the center of the view. The top of the surface moves inward (away from the observer), while the bottom moves outward. The phrase Rotate Down means a rotation about the same horizontal line, but in the opposite direction. The phrase Rotate Left means a counter-clockwise rotation about a line perpendicular to the center of the view. The phrase Rotate Right means a clockwise rotation about the same perpendicular line. These clockwise and counter-clockwise rotations operate in the same manner even if one or more rotate up operations has occurred first.
Starting from the initial state, in which the observer is looking directly down on the center of the region, the surface can be rotated a maximum of 80 degrees left or right, and/or 80 degrees up.
OVERHEAD VIEW OF CRATER, CLEOMEDES
Clicking on the Rotate-Up toolbar button provides an oblique 3D View of the area, (as shown). Clicking on the Rotate-Down toolbar button is used to reverse the process.
Once you have created a 3D View, you can use the Rotate-Left or Rotate-Right toolbar buttons to change the viewing angle of the feature. The toolbar buttons each rotate the map in opposite directions.
The surface cannot be rotated down, unless it is first rotated up. Once an orientation limit is reached, clicking the corresponding menu item or button has no effect.
The relief exaggeration can be modified by clicking on either of two items under the Relief Factor Menu, or either of two corresponding toolbar buttons. Each click on the Increment Menu Item, or corresponding toolbar button, increases the relief exaggeration.
Each click on the Decrement Menu Item, or corresponding toolbar button, decreases the relief exaggeration.
The relief factor may be decreased until there is no exaggeration at all, or it may be increased to a maximum value of 15 times normal. Once one of these limits has been reached, clicking the corresponding menu item or button will have no effect.
The visual appearance, (wire mesh vs. realistic), can be modified by clicking on either of two items under the Appearance Menu Wire Frame and Realistic, or either of the two corresponding toolbar buttons. .
If the appearance is currently wire mesh, clicking the Realistic Menu Item, or the corresponding button, results in a switch to the realistic appearance. If the appearance is currently realistic, clicking on the Wire Mesh Menu Item, or the corresponding toolbar button, causes a switch to the wire mesh appearance.
On the Point-of-View and Orientation Sliders, the tic marks are at 10-degree intervals. On the Zoom Factor and Relief Factor Sliders, the tic marks represent single-unit steps in the factor size. The control limits are marked above the sliders, at each end.
Each of the sliders makes it possible to set particular values for all the corresponding viewing parameters at one time, rather than in several increments, as with the menu or toolbar controls. In addition, all but the Relief Factor Slider provides much finer control of the image than the menu or toolbar controls.
The Point-of-View can be set to any latitude and/or longitude desired, rather than just those that are associated with a 25% shift. The Orientation can be set to any values in the permitted ranges, rather than just increments of 10 degrees. The Zoom Factor can be set to any integer value between 1 and 16, rather than just the powers of two that are possible with the menu or toolbar controls.
If you click on any of the Tool Bar Buttons or Menu Items, the corresponding sliders and text boxes on the Control Panel will adjust to correspond to the changes. To close the Control Panel, click the box containing in the upper-right-hand corner. Anytime the Control Panel is opened or reopened, the settings will reflect the current state of the 3D Viewer.
If you click on the File Menu in the 3D Viewer, you will be provided with three options.
If you click Copy, the image in the 3D display will be copied to your clipboard. You can then open a program such as Microsoft WordTM, and paste the image to your documents. Just open the Edit File in the new document, and click Paste. This feature comes in handy, when you want to include graphics in your written documents.
If you click Write Image you can save the 3D display, as a JPEG Image. This is a useful feature when you want to create a folder of images for later use. JPEG Images can also easily be placed into documents, or sent over the Internet.
Clicking Write Image displays the Save As Dialog Box. The Save in Window will generally display your WindowsTM Temp Directory as the default file folder. The default file name is Image.jpg. To store an image in a folder, name the image in the File name Window, and click the Save Button.
Clicking Print or clicking the Printer Icon will open your Printer Dialog Box, and allow you to print a hard copy of the 3D Image in the viewer.
Once you have mastered the 3D Viewer features, it will be possible for you to create, print, and copy 3D images of lunar features, such as those shown in the examples below.
Theophilus and Cyrillus
Plato and the Alpine (