Document TUFLOW format variant

[leonhard-s]

While looking for reference meshes to include in the unit tests, I encountered several non-standard card identifiers and card formats I was not familiar with. These seem to be specific to TUFLOW projects; the most important deviations from the standard are listed below:

• The occasional existence of a card NO_MOVE_EQ9_CENTER_NODE - no idea what it is used for.

• The initial MESH2D line contains extra columns containing georeferencing information.

  MESH2D  292725.000  6177615.000  -13.165794  200  170  5.000  5.000  10.000
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

  I found this post on the TUFLOW forum explaining what those columns are used for:

  [...] X-Origin, Y-Origin, Orientation in degrees relative to East, Number Cols, Number Rows, X-Cell Size, Y-Cell Size, Height adjustment for 1D WLL output. The last one is so that 1D results appear on top of 2D results when viewing in SMS.

• Extra data points after nodes:

  ND         1      292940.043     6177590.372      53.754  2  0. 0. 0.
                                                            ^^^^^^^^^^^

  The 2 0. 0. 0. portion is not part of the 2DM standard and I was unable to find out what it's for.

• Extra data points after elements:

  E4Q      8483      8737      8736      8575      8576     1     86     52  2   1
                                                                  ^^^^^^^^^^^^^^^^

  The first entry is the ID, then follow four node IDs, the first 1 is likely a material ID. This leaves four extra values, 86 52 2 1.

• This too uses the MESHNAME "<name>" card, but the name itself is surrounded by double quotes.

These meshes likely originate from the TUFLOW to GIS utility and are meant for display of TUFLOW results in SMS or other GIS packages.

Any details on the custom format TUFLOW uses for its 2DM mesh export would be appreciated; I am not opposed to making its custom data available in Py2DM, assuming this information is useful in other environments to begin with.

[leonhard-s]

This post is the closest to a definitive specification of the TUFLOW format, but it is not an official source and covers none of the special tags mentioned above.

The screenshot and information seem to originate from the TUFLOW user manual, build 2019.01 of which can be found here. The sections regarding the mesh format start at page 104 (chapter 8.1.2) but do not appear to specify anything that is not also in the SMS 2dm specification.

It should be noted that it also does not mention the MESHNAME <name> card despite using it (the 2DM standard uses GM <name> instead).