Examination of slices of three-dimensional data can also be done in the same manner as two-dimensional data. Start with a clean canvas (select New on the File pull-down). Wire Import to Slice to Projections to AutoColor to Collect. Connect WorldMapProjections to Collect. Wire Collect to Image. Double-click on Import. Enter "tropo_temp.dx" for name, and 0 for start and end. These data are 2.5 degree averages at seven pressure levels with global coverage. Double-click on Slice, which does dimensional subsetting. For the second input, dimension, enter a 2 for the third dimension (i.e., enumerated from 0). For the position, enter a 0. This will select the 1000 mb pressure level. For Projections and WorldMapProjections, enter 5 for the projection type -- north pole orthographic. Hit Execute-Once. You will now see the 1000 mb temperature map for the northern hemisphere in a polar orthographic projection.
The examination of two-dimensional data or slices of three-dimensional data can also be done in three-dimensions (i.e., in spherical coordinates). Double-click on Projections and WorldMapProjections, enter 7 for the projection type -- spherical. Hit Execute-Once. You will now see the 1000 mb temperature on a sphere with a map. You may choose to rotate the sphere to select an arbitrary geographic view.
Three-dimensional data can also be studied with volumetric techniques. Disconnect Slice, Projections, WorldMapProjections and Collect. Wire Import to AutoColor to Scale (Rendering category) to Image. Since the zaxis is pressure in mb, which has a different range than latitude and longitude, Scale will allow you to change the shape of what is rendered to support better viewing. Double-click on Scale. The vector input allows you to define a scale factor in each dimension. Enter [-1 1 -.18] for these data. Hit Execute-Once and an image will be generated. This is not an ideal view of these data. First specify an axes box with the AutoAxes selection under Image Options (x = Latitude (Degrees N.), y = Longitude (Degree E.), z = Pressure (mb)). Then under View Control, select Off Bottom under Set View. The image will be rendered with axes and a more appropriate view, which you can further adjust. Depending on the machine you are using, this operation may take a few minutes because you will be doing a direct volume rendering on the temperature data.
The volumetric data can be examined in a number of different ways. Connect Slab (Import and Export category) between AutoColor and Scale. Double-click on Slab and enter 2 for the second input, dimension, and 0 for the fourth input, thickness. Slab will separate a data set like this into a set of two-dimensional slabs embedded in three dimensions. Hit Execute-Once. You will now see each pressure level pseudo-colored by the same color map. The planes are translucent so that you can see the underlying layers.
As with the two-dimensional examples, annotating the image with a map is appropriate. Disconnect Slab from Scale. Simply wire WorldMapProjections to a Collect with the output of Slab, and connect the output of Connect to Scale. For the last input of WorldMapProjections, enter [0 0 100] to place the map at 100 mb level, the highest layer in this data set. Hit Execute-Once and a map will be placed in the volume, automatically registered.
As with the two-dimensional examples, applying cartographic projections is appropriate. Wire Projections between AutoColor and Collect. Double-click on Projections and WorldMapProjections and enter 6 for the projection type. In Projections enter a 1 for the third input, dimension, to select treating the three-dimensional data as truely volumetric. Hit Execute-Once. You will now see a volume rendered cylinder with a map on top corresponding to an orthographic projection for the entire southern hemisphere.
If you place Slab back into the network after Projections and before Collect, and hit Execute-Once, then you will see a south pole orthographic map for each of the seven pressure levels.
For color-filled contours, rewire Projections after Import and then Slab. Connect Band (Realization category) between Slab and AutoColor, followed by Collect. Double-click on Band. For the second input, value, enter {180 .. 320 : 20} and hit OK. This will create contour bands every 20 Kelvin over a range of 180 to 320.
To examine the interior of this orthographic cylinder, you can introduce a mapping plane that you can orient as you please. Rewire Import to AutoColor to Projections to MapToPlane (Realization category) to Collect. Place a Probe (Special category) and wire it to the third input of MapToPlane. Hit Execute-Once, bring up the View Control dialog under Image window Options (ctrl-v) and select Cursors mode. You will see an entry for the Probe, which will have a corresponding cursor in the Image window. By moving the cursor position, you can change the orientation of the mapping plane, which will be an ellipse in this coordinate system.
To look at the mapping plane as color-filled contours, connect Band after MapToPlane, followed by AutoColor, and hit Execute-Once.
Another way to look at these data is by generating isosurfaces -- surfaces of constant value. Wire Import to AutoColor to Projections to Isosurface to Collect, and hit Execute-Once. You will now have an image of a greenish surface, which is the surface corresponding to the mean temperature in the volume.
To allow you to interactively select one or more specific values for computing isosurfaces, place a ScalarList tool on the canvas from the Interactor category. Wire the output of projections to ScalarList, and the output of ScalarList to the second input of Isosurface, value. Double-click on the ScalarList and you have created a Control Panel with a widget for supporting entry of values. Hit Execute-Once, and the list will be populated with a set of default values, and the isosurfaces at those values will have been computed and rendered. You may now choose to change the temperature levels that you want to examine.
To create a simple application which you can use to look at a daily animation sequence of one or more isosurfaces of atmospheric temperature in a south pole orthographic map projection, add a Sequencer to the program. Double-click on Import and release the start and end buttons. Now wire the output of Sequencer to the start and end inputs of Import. Double-click on Sequencer and enter 0 and 6 for the Start and End values to show a week of data. Choose the temperature value(s) that wish to see in the Control Panel. Now hit play on the Sequencer. Each day worth of data will be read from disk, surfaces computed and rendering. The results will be played back in an animation that will show the dynamics of the earth atmosphere. While the animation is running, you may wish to change the orientation of the orthographic cylinder or the isosurface values. In either case, these changes will automatically cause Data Explorer to recompute only what is required, and play the results.
