Duration: 15 minutes
One of the simplest ways to produce a semi-realistic 3D display is to take an air photo or satellite image and drape it onto a digital elevation model (DTM). The 2D image will mould to the 3D shape of the DTM, increasing the realism of the DTM. Doing this in a 3D perspective view with the appropriate lighting and background options will further enhance the realism of the display.
After this lesson you’ll be able to: · Drape an image onto a DTM;
· Toggle between perspective and orthogonal display modes; · Set a realistic sky background colour, and
· Control lighting and surface shininess.
Draping an Image onto a DTM
In the following exercise, which is revision of Exercise 5.2 in Part 2 – Displaying and Manipulating Data, you’ll drape an image onto your DTM as the first step towards producing a pseudo-realistic display.
Optional Exercise 1.1: Drape an image onto a DTM To drape an image we begin by loading the DTM wireframe:
1. Double-click the Wireframes object in the Vizex Forms tree. 2. Switch to the Input Data tab on the Wireframes dialog, and ensure
the Single option is selected.
3. Double-click the Type response and choose DTM.tdb from the list. Next, double-click the Name response and choose TOPO from the list. 4. Switch to the Draw Options tab. Ensure the Draw Style is set to 3D
Shaded and Use Colour Coding is disabled. With the DTM loaded we can now drape the image:
5. Switch to the Drape Options tab and select the Image option. 6. Double-click the Image file response (or click the browse [...] button)
and navigate to the Import folder. Select MMI_IMAGE.ecw from the list. 7. Vizex will automatically set the Georeference Source to Micromine
Notes:
Now that the settings are defined we can save them as a form set:
8. Click the Save As button and save a form set with the Title Topo DTM with airphoto.
9. Click OK to display the draped image on the wireframe. At this point the display should resemble the following illustration:
The draped appearance of the image will be more realistic if the image and DTM both contain enough detail. You must also ensure that the image is referenced to the same coordinate system as the DTM, otherwise it won’t drape properly.
You can optionally control the transparency of the DTM by changing the
Notes: you to control the amount of smoothing in the triangle edges by adjusting the Smooth Wireframe slider.
Limitations of image draping
Your graphics card controls the amount of detail that can be draped onto a wireframe. To inspect this amount, select Tools | Check Graphics
Configuration from the main menu. The Maximum texture size
shows the maximum amount of detail that can be draped. Images larger than this will be sub-sampled to fit.
Enabling Perspective Mode
If you’ve ever stood on a set of railway tracks you’ll know they appear to converge over distance even though they are actually parallel. Tracks that are straight over a long distance, such as on Australia’s Nullarbor Plain or the North American prairies, will ultimately appear to converge at a point near the horizon. This is known as vanishing point perspective and is one of the visual cues that we use to judge distance and depth in the real world. Vizex uses the same principle for producing a realistic 3D view: features that are further from the current viewpoint will be smaller than features close to it, and parallel lines will appear to converge over distance. You achieve this by selecting Perspective Mode on the View toolbar. Without it your 3D data will be drawn in orthogonal mode and will appear as a magnified view seen from a great distance.
However, Perspective Mode can be distracting when viewing a plan or vertical section, and can be downright misleading when you’re drawing interpreted or design strings. Because of this, Perspective Mode is not enabled by default.
You’ll inspect the effect of Perspective Mode in the next exercise.
Exercise 1.2: Enable Perspective Mode To enable Perspective Mode:
1. Click the Perspective Mode button on the View toolbar and inspect its effect on the data.
2. Use the Rotate Tool to turn the view in 3D so you are looking at the DTM from a low angle.
3. Toggle Perspective Mode on and off and inspect its effect. Note how the sense of depth is severely diminished when it’s turned off.
Notes:
Setting the Background Colour
The background colour is an important aspect of any realistic 3D display. The outdoor sky generally doesn’t appear black, white, or grey, so it’s desirable to use a sky-blue colour instead.
Vizex offers three different background colour modes, which are accessible from the View | Vizex Background Options menu:
· Simple: Displays a single background colour;
· Gradient: Smoothly grades between two colours from the top to the
bottom of the screen. This mode is useful for lessening the visual impact of using a single colour;
· Sky and Ground: Uses any combination of colour ramps or colour sets
to independently control the sky and ground colours. You’ll use Sky and Ground in the following exercise.
Exercise 1.3: Set the background colour To set the background colour using Sky and Ground mode:
1. From the main menu, select View | Vizex Background Options. 2. Select the Sky and Ground option.
The colours for Sky and Ground mode are already set by default, but it’s useful to inspect them before applying them to the view.
3. Right-click the Colour set response for the Sky Hemisphere and choose Edit from the pop-up menu.
Sky colours are defined in terms of altitude above the horizon, measured in degrees from zero (the horizon) to 90 (the zenith). Note that 0 and 90 do not appear as they are implied by the first and last ranges in the colour set. Also note how the sky is pale near the horizon, becomes darker as the altitude increases, and then becomes pale again approaching the zenith.
4. Click Cancel to close the colour set.
5. Inspect the Ramp settings for the Ground Hemisphere.
Ground colours are defined very simply, using a pale brown at the nadir (directly below) and slowly grading to a darker brown at the horizon.
6. Click OK to apply Sky and Ground mode to the display.
7. Use the Rotate Tool to turn the view in 3D so that the horizon crosses near the middle of the screen. Your display should resemble this:
Notes:
Sky blue?
The sky is a much lighter blue than many people realise, especially near the horizon. Additionally, the gradation of colour in the sky is not linear; instead the colour changes quickly within about 15° of the horizon, and much more slowly as the altitude increases towards the zenith (90°). The Sky Hemisphere colours have been created to accurately simulate this change of colour.
Controlling the Lighting
Lighting is another important aspect of producing a realistic 3D display. Select View | Vizex Lighting Options from the main menu to control the lighting in Vizex.
Vizex provides two types of light:
· Scene Light: One or more point lights that cast a glow evenly in all
directions, which can be positioned anywhere relative to the data; · Head Light: A point light that illuminates the data from the viewing
position, literally like the headlights of a vehicle. Because it always originates from the viewing position, shadows and highlights will change as you rotate the data in 3D.
In the following exercise you’ll add a third light to illuminate the hillsides from the south, which currently appear a little too dark.
Notes: Exercise 1.4: Add a light
To add the light:
1. From the main menu, select View | Vizex Lighting Options. 2. On the Vizex Lighting dialog, select Enable Light 3 and enter the
following values:
Prompt Setting
Azimuth: 180
Altitude: 60
3. Click OK to apply the new light and note the effect on the DTM as you do so. Your display should resemble the following diagram (compare this with Exercise 1.3):
4. Keep the view open in preparation for the next exercise.
Restoring classic Micromine lighting
Earlier Micromine versions used a different lighting model, which you may want to restore under some circumstances. For compatibility the Vizex
Lighting dialog contains form sets for both Version 11 and 2010 default
lighting. You can easily switch between them by clicking the Forms button and choosing the desired form set.
Notes:
Putting it all Together
Producing a visually appealing 3D scene is as much art as it is science. In addition to controlling technical aspects like draping, perspective, background, and lighting it’s also important to consider the artistic appearance of the view.
The most important technique for improving the appearance of a 3D view is to always use Perspective Mode and Sky and Ground lighting.
For an above-ground view it’s also essential to create an illusion of a real aerial view. Useful ways to do this are:
· Get close to the data so the screen hides the front, left- and right-hand edges of the DTM, creating the illusion that the DTM continues forever; · Position the viewpoint as if you were realistically flying above the data
at low altitude to create a sense of depth and drama, and
· Position the viewpoint so that the DTM hides the horizon, giving the illusion that it is the horizon.
The horizon that Micromine draws (between the sky and ground hemispheres) is situated at an infinite distance and an altitude of zero, just like the real horizon. You can’t change its position (just like the real horizon), so you may need to use other methods if you can’t hide it using the tips above.
You’ll apply the techniques for creating an aerial view illusion in the next exercise.
Hiding the Horizon
The best way to hide the horizon is to extend your DTM well beyond the project area. If you don’t have enough data to do this you can either “invent” temporary data just for the 3D presentation, or download regional digital elevation data from an online source. Government organisations like Geoscience Australia (GA), the United States Geological Survey (USGS), and the Shuttle Radar Topography Mission (SRTM), amongst others, are good sources of free elevation data, although you may need to use GIS software to convert them into a format that Micromine can understand.
SRTM data are available for most of the earth’s surface within 60° north or south latitude.
Sky and Ground lighting may be inappropriate for an underground view depending on the extents of the surface DTM. However, you can still create a sense of depth and drama by positioning yourself next to and looking along a drive, heading, or stope to make use of the converging parallel lines.
Notes: Exercise 1.5: Create a realistic 3D view
We’ve already done the preparatory work for the 3D view so the only remaining task is to position the viewpoint in such a way that we create the illusions described above.
1. Rotate, pan, and zoom the data until you produce a satisfactory view. Your display might resemble this:
2. Compare this view with the one shown in Exercise 1.4, and keep it open in preparation for the next lesson.
Although the change in viewpoint is subtle it has a major effect on the illusion of reality. Within the limits set by the available data this view does almost look like a photograph from the window of a low-flying aircraft, even though we know the DTM stops just beyond the screen. In comparison, because the edges of the DTM are visible in Exercise 1.4, that view looks more like a model in a transparent box.
Changing Surface Shininess
The Vizex Lighting dialog also allows you to set the surface shininess of objects such as grids, block models, and wireframes. Shininess is of limited value when you’re creating a realistic 3D display but it is very useful for revealing subtle texture in surfaces with little relief.
For example, consider the following scene (containing a topographic DTM from a different project), which uses a headlight with no shininess. This lighting model clearly reveals large features in the hilly terrain, but the flat terrain to the right is almost completely featureless.
Notes:
In comparison, the scene below uses directional lights with around 30% surface shininess. Note how a great deal more texture is visible in the flat area to the right.
If these images had been of geophysical data you would expect to derive a great deal more structural information from the second image, especially in areas with low geophysical relief.
Notes: Lesson 1 Summary
In this lesson you learned to create a realistic display. To load a DTM and drape an image:
Double-click the Wireframes object in the Vizex Forms tree, then Choose the appropriate Wireframe, and
Switch to the Drape Options tab, then Load the image file, and
To enable Perspective Mode:
Click the Perspective Mode button on the View toolbar. To change the background colour:
From the main menu, select View | Vizex Background Options, then Choose the appropriate background mode, and
Set the appropriate colour(s) or colour set(s). To control the lights:
From the main menu, select View | Vizex Lighting Options, then Enable or disable a Scene Light or the Head Light as needed, and Enter the Azimuth and Altitude of the desired Scene Light. To change surface shininess:
From the main menu, select View | Vizex Lighting Options, and Drag the Object Shininess slider to the appropriate level.
To produce a visually pleasing 3D view:
Always use Perspective Mode and Sky and Ground backgrounds, and
Create an illusion of realism by getting close to the data, so that: The edges of the screen hide the edges of the DTM, and
Notes: Lesson 1 Summary (Continued) Good Practice
Remember that creating a pleasing 3D view is as much art as it is science, so take some time to consider the best viewpoint.
Many organisations provide free elevation data, so consider searching online if you need to extend your DTM to create a better 3D view.
Help Topics
For information on: See:
View toolbar View > Viewpoint > View toolbar
Creating a DTM (Vizex) [Index] > DTM > Create from strings or points Creating a DTM (Menu) DTM > Creating a surface
Images Display > Vizex > Image > Load and display an image Background options View > Vizex Background Options Lighting options View > Vizex Lighting Options
Notes: