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 base class for all parsers should be ModelParser. It contains some essential methods for using parsers and has a list of Triangles and Lines loaded from the model. So each parser should store the loaded data in the Group (which represents a Triangle/Lines mesh) member to keep everything simple. A group can has a name. It's mesh member stores the Triangle and Lines information. A Triangle can has texture and color. A line 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 parset 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

The collada parser uses [http://sourceforge.net/p/dae4j/ dae4j] library to parse the collada xml format. Currently dae4j hasn't implemented the whole collada specification, but it seems the best out there for java.

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

Check out ColladaParser for a sample implementation of a parser.

Steps to create a new model parser:

• 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 needed methods. These should be self explained (see javadoc)
• Store all data in Groups member of ModelParser parent.