We have taken depth measurements across a pond, and have a CSV file with each location's GPS coordinates and depth in meters. We are trying to create a map of this pond showing where the channel is and what areas have been filled in with silt (shallower). When using QGIS interpolation, the TIN method doesn't seem to work at all, and with the IDW method it is close to what we want, but is very patchy and incomplete. We want a smoother, more complete depth map of this pond. Can anyone explain what is happening in the TIN method picture, or explain how to obtain a better result?