# 2D Probe calculation

Problem:

What process does Tecplot use for probing? Also for streamtrace placement contour labeling linear interpolation and polyline extraction in 2D.

Solution:

In two dimensions Tecplot interpolates for dataset values at the chosen point using bilinear interpolation. For triangular cells, this is a straightforward interpolation of the three nodal values of the triangle that encloses the point:1. Determine the triangle that encloses the chosen point.

2. Determine the weighting to give each of the three corners of the triangle.3. Compute the weighted average to calculate the probe results.

For ordered and quadrilateral cells the enclosing quadrilateral is divided in half by drawing a diagonal line between opposite points resulting in two triangles. The triangle that encloses the point is identified and the values are interpolated as for triangles. But since there are two choices for which diagonal to draw, two different ways of dividing the cell in half, both diagonals are used and the interpolated values found with each diagonal are averaged to compute the final result.