Visualize objects using CAD models

This should be a quick start guide for using CAD models in KnowRob. CAD Models are used to show a realistic model of an object in KnowRob visualization (mod_vis). Please refer to the main knowrob tutorial (KnowRob_basics) for getting started.

Start KnowRob with the mod_vis package as argument:

rosrun rosprolog rosprolog mod_vis

Open the visualisation canvas:

visualisation_canvas(C).

Additionally load the knowrob_cad_models package that provides models and example links between object classes and CAD models:

register_ros_package(knowrob_cad_models).

Add an object instance to the scene:

owl_has(A, rdf:type, knowrob:'DrinkingBottle'), 
add_object(A, $C).

The visualization will automatically use a CAD model if one is specified instead of a generic visualization model.

CAD models can not only be used for visualization purposes, but can also serve as source of information about the geometry of the objects in the scene. For example, the dimensions of their bounding boxes can be read using the following commands:

Height of the model in meters

cad_model_zdim(identifier,Return).

Width of the model in meters

cad_model_xdim(identifier,Return).

Depth of the model in meters

cad_model_ydim(identifier,Return).

As a reminder, x = width, z = height, and y = depth. For a full list of query predicates check knowrob_cad_models/prolog/knowrob_cad_models.pl.

The system comes with parsers for Collada and .ply files. You can, however, easily write your own parser for other file formats.

The base class for all parsers should be ModelParser. It contains some essential methods for using parsers and stores a list of Triangles and Lines loaded from the model. Each parser should store the loaded data in the Group (which represents a Triangle/Lines mesh) member variable. Each group can have a name. Its mesh member variable stores the Triangle and Lines information. Triangles can have a texture and a color, Lines only a color.

The model parser is used to parse a CAD Model from a given file and is the base class for all parsers. The parser loads a file and “converts” it so that it can be stored as a list of triangles and lines.

A special feature of the ModelParser is buffering: If a model has been parsed it will be stored in a model buffer. So if the same model should be parsed again it will be taken from this buffer instead of parsing it again. Keep in mind that if you change something in a Group of a specific model it will affect all the other existing instances of this model.

Currently the following file formats are supported:

• Collada: *.dae, *.kmz
• Polygon File Format: *.ply

The collada parser uses the dae4j library to parse the Collada XML format. The current version of dae4j has not yet implemented the whole Collada specification, but still seems to the best Collada parser library for Java.

.kmz files are compressed Collada files (zip) and will be extracted into a temporary directory and parsed from there.

Check out ColladaParser for a sample implementation of a parser. The necessary steps for creating a new model parser are:

• Create a new class and extend it from ModelParser
• Add your parser to the extension list (In ModelParser.java) so a file extension will be assigned to your parser:
  • Example:

    extensionAssignment.put("dae", ColladaParser.class);

• Implement the required methods. These should be self-explaining (see javadoc)
• Store all data in the Groups member of the ModelParser parent class.