Select Theme 
□ose Ok Current theme = mat 
Façade of the nave of Antwerp Cathedral, material theme in construction and query on areas 
Attribute themes may group information on materials, pathology or construction phases. They are not imposed but created by the 
users, according to their needs. Themes are further divided in layers related to the attributes types (stone and wood in a material 
theme for instance). When a new theme is created, a layer 'unknown' is automatically assigned to all the triangles. The user must then 
create specific layers and qualify the geometry relating triangles to layers. This is a two times process: making a selection and 
choosing an attribute to apply to the selection. The colours of the deselected elements become lighter to give a feedback to the user. 
Different options are available to define a set of geometrical data. Triangles can be selected (or de-selected) one at the time or using 
polygons (inscribed or round). A selection set can be redefined by intersection, union or difference with the triangles belonging to a 
given layer. It can also be inverted, made empty or include all the triangles. With this system it is for instance possible to select 
elements inside a given area, built in stone and prior to a given construction stage. As the model's construction progresses, adding 
new attributes becomes therefore easier. Small Tel scripts can be written with all the commands necessary to easily reuse selection 
sets. 
When a selection is made, an attribute can be assigned from the list of existing attributes (layers) from the active theme. The selection 
set remains active until the complete set is reselected. So more attributes can be applied to the same set. One element complicates the 
process: feature edges may not correspond to triangles edges. The transition line between brick and stone may for instance fall inside 
a triangle. If the triangles were very small (their dimension being of the order of magnitude of the details), it would not be so 
important, but it is unlikely to be so. A tool was therefore devised to refine the mesh. It uses a cutting segment defined on the model 
with the mouse. The triangles created receive by default the attributes and texture from the original triangle. 
2.2 Vector graphics 
Points and segments can be drawn. They are placed in the active layer of the active theme. They are drawn via picking or via 
coordinate introduction. Display points defined by the mouse (2D) are projected on the model (3D). It is possible to draw a segment 
connecting the two 3D points so defined or a 'polyline' intersecting the model. These tools allow the user to draw very quickly the 
joints of a stone, cracks or any other 1-dimensional features. 
Section can also be drawn, selecting or defining a plane (via 3 points). The easiness of the process allows the user to quickly search 
for the best position. In just one command, it is possible to generate iso-lines of a vault. 
Geometries can be imported and exported via DXF files. Of course, only the limited number of spatial elements supported could be 
imported. Original layers are mapped on layers of the active theme. If the names do not match, new sub-layers are created.