CRT – cloud model

Spherically symmetric models

Model is defined using a separate file that is named using the `cloud1d` keyword of the ini-file.
A spherically symmetric cloud consists of co-centric shell and we need to specify only the radie and densities of the shells. Unlike in the line transfer program Cppsimu the values can not be given via analytical formulae. Values must be listed shell by shell as in the following example:

# number of shells
10
# [ outer radius, density ] n ~ 1/r
0.25 0.8
0.40 0.7
0.52 0.6
0.65 0.5
0.78 0.4
0.85 0.3
0.90 0.2
0.94 0.15
0.97 0.1
0.99 0.05
1.00 0.05

The radiae (first column) are relative values and the last value should be 1.0. Densities can be re-scaled using in the ini-file the keyword `density`. In CRT the centre coordinates of a spherical cloud are (0.0, 0.0, 0.0) and the positions of for example internal sources are defined in coordinates where the cloud radius is 1.0 units.

Cylinder symmetric models

These can be specified still using ascii files. The first two lines contain the number of radiae and number of planes. These are followed, one value per line, by the outer radiae of the cylindrical cells (the last one should be 1.0) and the coordinates of the upper boundaries of layers that are used to divide the cylinder into cells perpendicular to its symmetry axis. The cylinder starts implicitly at 0.0 and only the coordinates for the upper borders of the layers are specified, the last number thus giving the height of the cylinder (relative to the radius that is assumed to be 1.0 units). These are followed by the density values, one number per line, starting at the bottom of the cylinder so that the radial cell index runs faster that the index of the planes.

In CRT the coordinates (0.0, 0.0, 0.0) correspond to the bottom of the cylinder (on the surface of the model), at the symmetry axis, the radius of the model is 1.0 units, and the height as specified above. The centre of the model is thus (0.0, 0.0, `height`/2.0). These coordinates are used when placing for example internal sources. The physical size is given with the keyword `gridlength` (see the documentation for the ini file).

Three-dimensional clouds

A 3D cloud is defined using a simple binary file. File starts with three integers (3 x 4 bytes) giving the cloud dimensions as cells (`NX,NY,NZ`). The following values (4 byte floats) give the density for each of the cells. The x-coordinate runs fastest, i.e., the consecutive numbers correspond to cells with indices (0,0,0), (1,0,0), (2,0,0), …, (`NX`-1,0,0), (0,1,0), (1,1,0), …, (`NX`-1, `NY`-1, `NZ`-1).

In CRT the the size of a cell is 1.0 units along all three axes. The first corner is at (0.0, 0.0, 0.0) and the cell at the corner extends over coordinate values 0.0-1.0. For example, If a source is placed at the centre of the model volume, its coordinates (see keyword inside) are (0.5*`NX`, 0.5*`NY`, 0.5*`NZ`).