Modify Grid Prep tab --> point, line, polygon digitization

Right now the grid tab only lets you set up points in a regular pattern. Proposed new capabilities:

• Add custom points

  1. Digitize points wherever the user clicks

• Add a cross-section line tool.

  1. Digitize the line
  2. Space nodes along the line

• If XS geometry exists, add a cross-section line of the correct length

  1. Digitize the line, but use the supplied known line length
  2. Space nodes along the line

Notes

Although not a part of this issue, eventually, we will want to visualize feedback to the user concerning the image velocimetry methods.

• If using STIV, this would mean plotting the search lines for each (or some subset of) points
• If using PIV, this should be the search/interrogation windows