Grouping DTM Triangles
It is often necessary to group triangles that have a common function or property and there are a number of different situations where this is useful. For instance, you may wish to group together certain areas where different materials are stockpiled, such as sand or gravel, for stocktaking purposes. It may be that the model is being used for earthwork calculations for a commercial development where there are different construction depths for different areas, such as foundation slabs, footpaths and car parks. Groups can also be used to identify the different areas on a housing development so that stormwater run-off calculations can be carried out. They are also useful in the identification of the different construction or excavation phases of design. A final example of their use is the identification of areas where you do not wish contours to be displayed, such as building footprints or very steep slopes.
DTM Group Settings
To identify groups, each triangle that has been added to a particular DTM group will be shaded using the fill pattern that has been assigned to its group. The Group Settings option allows you to create DTM groups and specify how they are to be displayed. The Settings menu in each model will also contain an option called DTM Groups which performs the same function. When selected, the dialog box to the right will be displayed.
To the left of the dialog is the Groups group which contains list of DTM groups that have been defined. The Add and Remove buttons allow you create new and remove existing groups. If you remove a DTM group, all triangles that are assigned to it will be reassigned to have no DTM Group.
Highlighting a DTM group in the list will change the contents of the Properties group to those of the selected DTM group. The Layer and Fill Style fields define the basic attributes for display purposes. The Depth field allows you to assign a depth to any DTM group. This is used in volumetric calculations where you have final design levels and construction depths. Earthwork volumes can then be calculated to formation level without having to take off construction volumes. The Display Contours check button allows you to specify whether contours are displayed or not. If the contours are to be displayed, the Offset Contours by Depth check button allows you to display the contours taking into account the DTM group depths.
Each project has a default set of DTM groups which are loaded from the default settings when the project is created. The Load button allows you to load DTM groups from that default set into the current model. It also allows you to save DTM groups that have been created in the current model into the default set. When selected, the dialog box to the right will be displayed. Highlighting groups in each list and using the arrow buttons allows you to copy the groups between the defaults and the model and vice versa.
The same DTM Groups dialog box is also used to create and remove DTM groups from the default set for the current project. The only difference is that the Load button is replaced by a Save button. This enables you to save the current projects DTM groups into the settings file that is used when a new project is created.
If the pick mode is set to lock any change cannot take place. Similarly, when removing triangles from groups, you cannot remove triangles that have been locked.
The boundary pick mode creates a Feature from the Extent of the indicated Group.