The first three lines in the file are comment lines. The first two lines are automatically used as headings for plots. Next, there is a blank line, a line for the time unit of inflow / outflow rates and again a blank line. The subsequent line defines the model type. After another a blank line, the scale definition follows. Following yet another blank line, the datasets of the first group start. Here, the definition of elements or fractures always requires the definition of the corresponding nodes before. Then the other groups can follow. Within the groups, the order of data sets is not stipulated. The file ends with three blank lines. If one data type is missing, the corresponding dataset is not required in the file. In general, it is possible to have several data sets of the very same type in one input file. Each dataset consists of the identification line, the values and the final blank line. Between the data, no further blank lines are allowed. Each data type is characterized by a combination of four letters (capitals or small letters). This identification is written into the first four columns of the identification line. The line can be continued with individual comments (see the example).

The following graphic illustrates the structure of the model file:

Structure of the 3D extension file *.3d