Using Markers

The topics covered in this section include:

The Marker Editor

Selecting a Model to Edit

Like all of the model editing tools, the Marker Editor operates only on markers in the current model, visit Opening, Closing, and Using the Navigator Window for more information about how to make a model current. When you change the current model, the Marker Editor automatically switches to operate on this model, and displays the first marker in the model.

Selecting a Marker to Edit

To select a marker for editing, you must first make sure that the model containing the marker is the current model visit Opening, Closing, and Using the Navigator Window for more information about how to make a model current. 

There are three methods to select a marker. The first uses the Navigator window:

1. Expand the tree for the model to access the marker of interest. You can do this by clicking on the plus  sign next to the name of the current model to display the model components, and then clicking on the plus  sign next to Markers. In some models, the markers are organized into groups, in which case you will also have to click on the plus  sign next to the group containing the marker.
2. Right click on the name of the marker.
3. Choose Edit… from the drop-down menu, and the Marker Editor will update to show the properties of that marker.

The second method operates in the 3D View window. Press the ctrl key to enter selection mode. You will see the cursor change into a small crosshair to indicate that you are in selection mode. Keep the ctrl key pressed and left click on a marker to select it. If you also hold down the shift key, you can select multiple markers. The last marker you select will be displayed in the Marker Editor window and used as the current marker. To unselect all markers, press ctrl and left click on a point away from the model.

The third method of choosing a marker for editing is from within the Marker Editor window. In the top-left corner of the window, just below the model name, there is a box containing a list, sorted alphabetically, of all of the markers in the current model. The current marker is shown in the box. To switch to a different marker, left click on the box and choose another marker.

When a marker is selected, it is displayed in yellow on the 3D model, with a yellow line connecting it to the origin of the body to which it is attached. Also, its name is shown in the text bar at the bottom of the OpenSim window. If you select multiple markers, the last one selected will be made the current marker in the Marker Editor.

Editing Markers

To change the name of a marker, left click in the Name text field and enter a new name. If you enter a name that is already being used by another marker, an error message is printed. To change the body to which the marker is attached, left click on the Body box list and choose a new body.

The Marker Editor does not have a mechanism for changing the weights of the markers because this functionality is provided by the various tools that use markers. For example, the Scale Tool and Inverse Kinematics Tool contain Weights panels for specifying the weight of each marker during the scaling or inverse kinematics process.

Moving Markers

There are two methods for moving markers. The first method is to move them interactively in the 3D View window. Select the markers you want to move visit Selecting a Marker to Edit for more information on selecting markers. Move the cursor over any of the selected markers, and press the left mouse button. While holding the button down, you can drag the markers within the plane of the screen. All of the selected markers will move the same amount, so it does not matter which one you click on. To move the markers in a different plane, release the left mouse button, rotate the model view as desired, and then press the left mouse button on any selected marker to resume dragging.

The second method of moving markers is to type their exact XYZ offsets into the number fields in the Offset section. For this method, the markers do not need to be selected, but you can only modify the offset of the current marker. Click on the appropriate X, Y, or Z number field, and type in the desired value. These offsets are expressed in the reference frame of the body to which the marker is attached, which is shown above the Offset section.

Adding and Deleting Markers

There are two methods of adding markers to the current model. The first uses the Navigator window. Click on the plus  sign next to the name of the current model to display its components, then right-click on the Markers category and choose Add New from the drop-down menu. A new marker attached to the ground body will be added to the model.

The second method of adding a marker is to click on the Add New button in the Marker Editor window. This will also create a new marker attached to the ground body.
To delete a marker, first make sure it is the current marker in the Marker Editor window. Then click on the Delete Current button. This will delete only the current marker, not any other markers that are selected in the 3D model window.

Backing Up and Restoring

When you modify the name, body, or offset of a marker in the Marker Editor, the modification occurs immediately to the marker stored in the model. You do not need to apply the change to make it happen, nor can you cancel the change before it takes effect. To allow you to undo changes made to the markers, there are four buttons at the bottom of the Marker Editor window that backup and restore the states of the markers.

When you first load a model into OpenSim, the Marker Editor makes a backup copy of every marker, so you can restore them without having to back them up first. Here is a description of each button:

• Restore current – This button restores the current marker from its backup copy, thereby erasing all modifications you have made since the last time the marker was backed up. If the marker was added but not yet backed up, it will be deleted.

• Restore all – This button restores all of the markers in the model from their backup copies, thereby erasing all modifications you have made since the last time each marker was backed up. All markers that have been added but not yet backed up will be deleted.

• Backup current – This button makes a backup copy of the current marker, overwriting the previous copy.

• Backup all – This button makes a backup copy of every marker in the current model, overwriting the previous copies.