Arc/Info TIN to VRML

erich@museum.state.il.us
Erich Schroeder
Illinois State Museum
GIS Lab
Springfield, IL 62703

Modified:

Tue Feb 20, 1996
Fri May 31, 1996 (based on input from Chris Ferrier (clf@primenet.com)

• VRML Class (NCSA)
• VRML Repository
• You will need a browser.

My goal has been to create an easy method to move from Arc/Info TIN (Triangular Irregular Network) format into VRML. I figured that this should be possible because both are based on nodes, lines, and faces.

It turns out that ESRI is planning to provide a VRML generator with A/I Rev. 7.1! I will probably continue with this although it may prove to be unecessary in the future.

• My first example is a virtual Cahokia (also in Gnu-Zip format. In case you are not familiar, the Cahokia site is a very large pre-Columbian site located in the floodplain of the Mississippi River just east of St. Louis. Cahokia was the center of a way of life archaeologists call "Mississippian"--a way of life based on maze agriculture and characterized by elaborate political and religious structure. The tallest earthwork that you will see is known as Monks Mound, and is the largest pre-Columbian earthwork in North America north of Mexico.

  I have only tested it with VRweb running on LINUX. (there have been problems in the browsers I've used under MS-Windows) Hope it works for you, but I don't guarantee it yet.

• Tin2wrl.aml is the basic script. It is called in the format

  &r tin2wrl <tin>
  

  Where <tin> is the name of a previously-created Arc/Info TIN. Tin2wrl.aml runs two INFO programs.

• SETPOLYNODE4 is the most important of the two. This program identifies the three nodes that make up each triangular face. It uses several scratch INFO data files that you must define before running the aml. These all have the same structure:

  Arc: items polynodes
   
  COLUMN   ITEM NAME        WIDTH OUTPUT  TYPE N.DEC  ALTERNATE NAME     INDEXED?
      1  TNPOLY#                4     5     B      -                        -
      5  NODE1                  4     5     B      -                        -
      9  NODE2                  4     5     B      -                        -
     13  NODE3                  4     5     B      -                        -
     17  ENDNODE                4     5     B      -                        -
       **  REDEFINED ITEMS  **
      1  RPOLY#                 4     5     B      -                        -
      1  LPOLY#                 4     5     B      -                        -
   
  Arc: 
  

  And the files that you will created are called: LPOLYNODES, RPOLYNODES, POLYNODES, TMPPOLYNODES, and TMP2POLYNODES. They are all the same so you can just DEFINE one and copy them using the COPYINFO command in ARC . I imagine that in later versions I will make them real scratch files and the user will not have to define them. Currently there are lots of debugging messages displayed as the program runs.

• WRITEWRL does the VRML file writing. There might be better methods, but this works. CURRENTLY YOU MUST EDIT A SINGLE LEADING SPACE FROM THE FIRST LINE OF THE VRML FILE.

  In case you are a sane person (that is, one who is unfamilar with the strange and awkward world of INFO programming), I've put together a description of how to move the text versions of INFO programs into a compilable (hopefully) INFO program.

Future Directions

This interactive aspect of GIS is an continuation of my interest in animation of spatial information, and the representation of time. You might want to look at the under construction exhibit based on the Illinois Land Records, where I have several methods for displaying a series of time slices.