3D topographic map

Summary

Doc_BoxAlgorithm_3DTopographicMap.png
  • Plugin name : 3D topographic map
  • Version : 1.0
  • Author : Vincent Delannoy
  • Company : INRIA/IRISA
  • Short description : 3D potentials mapping using spherical spline interpolation
  • Documentation template generation date : Dec 30 2016

Description

The 3D topographic map uses the same visualisation paradigm as its 2D version, which consists in interpolating potentials (or current densities) at the surface of the scalp, converting them to colors using a color scale and mapping them over the surface of the scalp. The 3D version offers the possibility to freeky move around the head to observe brain activity from a custom point of view.

It requires a head model to be available. This model is divided in two : the lower part, which includes the face and the neck, is static (meaning once it's loaded, it doesn't get modified). The other part, the 'scalp', is the area where potentials are mapped. Its size and shape determine where brain activity mapping will occur once the plugin is running. This second mesh is a set of vertices whose colors will be modified depending on the value of the potential interpolated there.

Potentials interpolation works using a spherical spline algorithm. The coordinates of the electrodes used in the experiment are sent to the algorithm in an initialization step. Then as the experiment is conducted, the values of the potentials measured at the electrodes location are sent to the algorithm.

Potentials at scalp vertices locations can be retrieved by converting each vertex location (expressed in model frame) to a cartesian orthonormal frame.

Inputs

Note: the channel names specified on the 'Signal' and 'Channel Localization' input streams should match. Mismatches may not be reported by the box. For example, if electrode localisation file reader provides the positions of the electrodes from some configuration file, the channel names in that file should correspend to the names of the signal channels delivered in the Signal stream.

1. Signal

  • Type identifier : Streamed matrix (0x544a003e, 0x6dcba5f6)

2. Channel localisation

  • Type identifier : Channel localisation (0x013df452, 0xa3a8879a)

Settings

1. Interpolation type

Choice of spline or laplacian interpolation.

  • Type identifier : Spherical linear interpolation type (0x44b76d9e, 0x618229bc)
  • Default value : [ 1 ]

2. Delay (in s)

Delay to apply to displayed data, in seconds.

  • Type identifier : Float (0x512a166f, 0x5c3ef83f)
  • Default value : [ 0 ]

3. Face mesh filename

  • Type identifier : String (0x79a9edeb, 0x245d83fc)
  • Default value : [ face ]

4. Scalp mesh filename

  • Type identifier : String (0x79a9edeb, 0x245d83fc)
  • Default value : [ scalp ]

5. Sphere projection mesh filename

  • Type identifier : String (0x79a9edeb, 0x245d83fc)
  • Default value : [ projection_center ]

Online visualisation settings

Online settings include :

  • Map Potentials/Currents : these settings control the nature of mapped values. While potentials are computed from spline values, currents computation uses the spline laplacian.
  • Toggle Electrodes : toggle electrodes on/off.
  • Toggle Sampling Points : toggle sampling points on/off. Sampling points lie at the vertices of the skull mesh.
topographicmap3ddisplay_toolbar.png
3D Topographic Map toolbar

Examples

This example is based on the following scenario file : box-tutorials/topographic_map.xml

In this example an EEG recording is read using a GDF file reader, and data is processed and filtered before being mapped onto the scalp surface. For details on this data processing step, see the example in 2D topographic map.

A 2D topographic map is displayed next to the 3D version for comparison purposes.

topographicmap3ddisplay_2d_vs_3d_online.png
Mapping brain activity in 2D and 3D

Miscellaneous