Geometry Selection Functionality

An important part of working with geometry is being able to select subsets of larger models to work on. An example of this is BRL-CAD's search command, which can identify subsets of geometry based on filters of geometry type, name, depth in tree hierarchy, and other criteria. In addition, search can combine multiple criteria to match only geometry satisfying multiple criteria.

For this task, geometry selection refers specifically to the selection of geometric subsets that satisfy geometric location criteria such as "within this volume" or "projected area onto this plain is within this rectangle", typical operations for graphical selection of geometry in a window. Rather than implementing this logic at the graphical level, the goal would be to program a C API that would accept as arguments a list of geometry paths and geometric filtering criteria. This function should not be aware of the client modeling application's view state directly - any such information should be passed into the function as part of the filtering criteria. The target product would be a C api in librt (possibly an extension of the existing search code filter types, if that proves appropriate) and a command line utility (either new search options or a select command) that exercised them. Graphical integration is a separate topic, and would require this task to be completed first.

A proposal for this task should outline candidate selection criteria to implement and an implementation strategy - issues to consider include how to specify filters with geometric criteria on the command line, how to handle view information, and mechanisms to test using implicit geometry (for example, the projected rectangle case above may require an approximation using bounding box volumes if the unevaluated primitive doesn't contain enough information to project an area onto a plain without raytracing or format conversion.)


  • src/libged
  • src/mged
  • include/ged.h
  • src/libtclcad


  • Familiarity with C
  • Good grasp of geometry (projections onto plains, etc.)