Topographic Interpolation

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Instructions on how to do Topographic Interpolation can be found in the BVA Manual in section 12.7.4. Though they are pretty clear on how to apply the transformation, there are a few things that may need some clearing up:

  • Keep Old Channels checkbox: In the top right corner, there is a checkbox that asks to Keep Old Channels. If you want to keep the rest of the channels you are not interpolating and the newly interpolated ones, select this box. This box does not mean that the program will keep the channels you want to interpolate pre-interpolation and post-interpolation. If you do not select this box, then only the interpolated channels will be preserved and the rest of the channels that were not interpolated will not be seen. Therefore, we recommend keeping this box selected when performing topographic interpolation.
  • New Channels on Top checkbox: If this is selected, it moves the newly interpolated channels to the top of the channel viewing window once interpolation is completed. This means that these channels will be displaced from the original channel order. If you want to leave the interpolated channels in order with the rest of the non-interpolated channels, keep this box unchecked.
  • Triangulation and Linear Interpolation vs. Spherical Spline Interpolation: Basically, this is up to the researcher. We've found in the Cohen lab that the Triangulation and Linear method makes the topo plots less smooth while the Spherical Spline results in smoother topo plots. If using the Spherical Spline Interpolation, we recommend using the default settings for the order of splines (4) and the maximum degree of Legendre polynomials (10) and keeping the Default Lambda (1e-5) checked. The setting of these two interpolation setting are explained in the BVA manual. More information about determining the best order of splines for interpolation can be read here in this article from the University of Oregon.
  • Deleting channels before interpolation: In the BVA manual, they recommend the use to delete the old channel before interpolating it; however, this can get messy because if BVA can't locate the channel, it won't interpolate it and it's more work for the user. What we've found is that BVA will replace the old channel with the new interpolated channel, so there's no need to delete the channel from the data set before interpolation.

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