Project 1: Allan Spale (aspale@evl

Project 1, CS 526: Allan Spale (aspale@evl.uic.edu)

Background

This program was written using Python 2.1, VTK 4.2, and Tkinter (a Python module that supports GUI widgets). The files for the project are simply project1.py. To run the program, type the following: python project1.py. Since Python is an interpreted language, there is no need to compile; although there is an ability to compile a Python script to decrease the startup time. The program meets most of the basic requirements for displaying the requested visualizations. Some additional functionality was provided which will be described in the next section.

Sources

The sources of information used to create this code include the following:

· Python in a Nutshell, ISBN 0596001886 (used source as guideline to construct GUI classes and for creating other widgets)

· VTK Book, ISBN 1930934076

· Websites

o An Introduction to Tkinter (very useful for figuring out how to use Tkinter)

o VTK Docs

o Python Docs

· VTK Tk/Tcl example code (invaluable for figuring out usage of VTK)

Usage

With the combination of Tkinter not being a very good GUI and my inexperience with Tkinter, the GUIs provided for the program are a bit “rough” and spartan. Nevertheless, the program still generally functions as one would expect without too many surprises. One problem is that I could not create modal dialogs. This means that any dialog that appears will not require that the user close it before returning to the main window. Secondly, in order to update the visualization, it is necessary to click in the rendering window. It is very important to make sure that the user selects a visualization from the Visualization menu immediately after opening a file because by default NOTHING appears. Once the user selects a visualization, make sure to try to zoom in on the elevation and click a few times in render window to make sure that the elevation appears. Third, the only way to get contour lines alone is to choose that as the first visualization. Otherwise, the contour lines will appear on whatever elevation map is currently displayed. Finally, there is no serious error checking.

The only supported file format is RAW. Any RAW grayscale or RGB texture may be input as long as it is 2-D and its dimensions (i.e. width and height) are known. Once the user has finished looking at files, it is strongly recommended that they exit and restart the program.

Menus

· To open a file, select Open. The only supported file type is RAW. Enter the file name, the image dimensions, and whether or not the file is grayscale or RGB. This is done for both the texture and the elevation map. To quit the program, either close the main window or select Exit.

· To visualize the data, select one of the menus from the Visualization menu. The available options are Colormap, Contour Lines, Grayscale, and Texture.

o Colormap uses a predefined colormap that goes from dark colors to light colors. Additionally, the lower value elevation locations will be less opaque than higher value elevations. However, this only seems to work on early attempts before any other visualization modifications occur.

o Contour Lines presents a dialog box to configure each of four contour lines colored by default red, blue, green, and yellow. By selecting a radio button with the color name, the user can then change the height of the contour in addition to the thickness of the contour line. For the changes to appear, it is necessary to click in the rendering window. A side effect is that the contour lines will appear on any other visualization chosen after this one. To make the contour lines go away, it is necessary to make another selection from the visualization menu that is not Contour Lines. In order to display the contour lines alone, make this the first selection.

o Grayscale will display the elevation map according to the texture provided by the elevation file.

o Texture will display the elevation map according to the texture provided by the texture file.

· To change some of the options of how the elevation appears, select the Options menu.

o Selecting the Landscape menu brings up a dialog box that allows the user to change the warp factor of the elevation between a range that is both negative and positive. Additionally, the user can reduce or increase the subsampling factor of the data. A higher value will improve performance but also lower the resolution. Once the user makes a selection, it is necessary to click in the rendering window in order for the changes to take effect.

Design

There is a class that takes care of all of the rendering. In the constructor part of this class, all of the visualization pipeline parts are created, but not all of the attributes are set. Below is a general overview of the pipelines…

readerTexture (vtkImageReader2) -> shrinkTex (vtkImageShrink3D)

readerElev (vtkImageReader2) -> shrinkElev (vtkImageShrink3D) -> geometry (vtkImageDataGeometryFilter) -> warp (vtkWarpScalar) -> merge (vtkMergeFilter)-> mapperStandard (vtkDataSetMapper)

colormap (vtkLookupTable) -> elevation (vtkElevationFilter) -> colormapMapper (vtkPolyDataMapper) -> actorColormap (vtkActor)

contour_X (vtkContourFilter) -> contour_X_mapper (vtkPolyDataMapper) -> contour_X_actor (vtkActor)

ren (vtkRenderer) -> renWin (vtkRenderWindow) -> rw (vtkTkRenderWindowInteractor)

Depending on the circumstance, these pipelines will be connected as needed. One case is taking shrinkTex and sending it to merge to apply the texture to the elevation map.

Bonus Features

Contour lines may appear on any elevation texture. Choose Contour Lines after using another visualization.
Contour thickness can be manipulated from 0 (hidden) to 5 pt thickness.
Subsampling data is provided for better performance using the Landscape dialog box.
Colormap that uses alpha values to permit sight through large surfaces.

Deficiencies

Special case needed to have contour lines appear on their own (i.e. must be first visualization selected in a session).
As the height map is warped, the colormap changes.
There is only support for the RAW file format with known dimensions.
The program can only be started to view a single visualization. Once the user has finished viewing the files, the user must restart the program in order to open the new elevation and texture files.