Editing Vtk/SimpleCubeTutorial (section)

===Reading Cube Model from a Local File===
You will be afforded a much greater degree of design flexibility if, rather than asking VisTrails to download the file from a web site, you create a local file (on the same computer that you are using to run VisTrails) that contains the POINTS and POLYGONS defining the cube and instruct VisTrails to read the information from that local file.  Initially, the file need only contain the 20 lines of ASCII text that are displayed in the left-hand panel of the above "Minimalistic Cube" figure.  

1.  Create a new file on your computer and either (a) type the 20 lines of ASCII text into the file by hand, or (b) copy the ASCII text from the "SimpleCube_Step01.vtk" file provided at the above-referenced web site and paste that information into your new file.  
* Be very careful doing this because the "vtkPolyDataReader" module in VisTrails is very picky.  In order to guarantee success, the file should be formatted in precisely the manner used here, that is, using the ''Simple Legacy Format'' described in &sect;15.3 (pp. 324-336) of the [http://www.kitware.com/products/books/vtkguide.html ''VTK User's Guide''].  
* For the purposes of this tutorial exercise, when you save the file, name it <font color="darkgreen">''TestCube01.txt''</font>; to comply with the ''Simple Legacy Format'' standards, be sure to save it as a "text only" file.

2.  Point the "vtkPolyDataReader" module to this new file:
* Disconnect (and, if desired, delete) the "HTTPFile" module from the VisTrails pipeline.
* Click on (''i.e.'', highlight) the "vtkPolyDataReader" module in the pipeline, then drag the "SetFile" method into the "Set Methods" segment of the VisTrails Builder Window.
* A small folder icon will appear immediately to the right of the newly created "File" text window; click on this icon, then march through your computer's file folders to find your newly created <font color="darkgreen">''TestCube01.txt''</font> file.

3.  Executing this modified pipeline should, once again, generate the tomato-colored cube as shown in the right-hand panel of the above "Minimalistic Cube" figure.

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<font color="red">'''CAUTION (from J. E. Tohline):'''</font> This simple step caused me considerable grief when I was first trying to understand how to enlist VisTrails in my research activities.  I already understood how to numerically define the vertices and polygons of a desired wireframe model for, say, a three-dimensional isodensity contour of one of my group's astrophysical fluid flow simulations.  But I had difficulty figuring out how to write that information to a file in a format that VisTrails could understand.  

In an effort to minimize typing mistakes, I searched for a web site from which I could copy-and-paste the entire "Cube example" provided on pp. 331-332 of the [http://www.kitware.com/products/books/vtkguide.html ''VTK User's Guide''].  I discovered that the entire "VTK File Formats" discussion from the VTK User's Guide was posted on a [http://www.cacr.caltech.edu/~slombey/asci/vtk/vtk_formats.simple.html Caltech website], but my copy-and-paste operation introduced quite a few additional white spaces &#8212; and deleted others &#8212; at locations within the text file that violated rules established within the context of the ''Simple Legacy Format.''  As a result, the "vtkPolyDataReader" module misinterpreted the information and, as a consequence, the VisTrails pipeline failed to generate an image.  This was difficult to debug because I had no idea whether the data file was corrupted or whether I had screwed up the design of the VisTrails pipeline.

If you are able to successfully generate the tomato-colored cube by using the "HTTPFile" module to download the "SimpleCube_step01.vtk" file from the above-referenced web site but you are not immediately able to generate the same tomato-colored cube by calling upon the "vtkPolyDataReader" module to directly access your newly created text file, it is very likely that your file does not strictly conform to the ''Simple Legacy Format''.  Check to make sure that the file you have created does not have hidden formatting instructions, such as unwanted forced line feeds.
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4.  After you have successfully generated the tomato-colored cube by reading the cube model in from a local file, you should change the extension of the file name from ".txt" to ".vtk".  This should be done because (see the opening paragraph of the "Dataset Format" discussion on p. 326 of the [http://www.kitware.com/products/books/vtkguide.html ''VTK User's Guide'']), by convention VTK files written in ''Simple Legacy Format'' use the .vtk file extension regardless of the dataset type contained in the file.  After making this change, repeat steps #2 and #3 to make sure you can still generate the minimalistic cube.