This document describes HydrOffice QC Tools 4.9.9.

2.3.5.2. How Does It Work?¶

The Depth, Uncertainty, Density (if available), and a computed Total Vertical Uncertainty (TVU) QC layer are used to compute particular statistics shown as a series of plots.

The following plots are the output of Grid Stats:

The Density layer is plotted as a distribution (plot entitled “Density Distribution”).
- Percentages of nodes less than 5 soundings per node fall in the red shaded region of the plot and together must be less than 5% of all nodes in order to “pass”.
TVU is plotted as a distribution (plot entitled “TVU QC Distribution - NOAA [OCS Quality Metric]”).
- Percentages of nodes with TVU QC greater than 1.0 (indicating that the allowable error has been exceeded) fall in the red shaded region of the plot, and together must be less than 5% of all nodes in order to “pass”.
TVU analysis across NOAA OCS Quality Metrics are plotted in the “TVU QC Overview”.
Only for Variable Resolution grids, a histogram with the percentage of nodes at the prescribed resolution is created. This histogram can be used to evaluate whether “[a]t least 95% of all grid nodes must have a resolution equal to or smaller than the minimum required resolution for the node depth/height.” (NOAA HSSD). The resolution is determined by the Feature Detection selection made in the the Survey Requirements section in the Input Tab window.

TVU QC Calculations

The TVU QC layer is calculated on-the-fly by the program. TVU QC based on OCS Quality Metrics for Uncertainty (as defined in the 2024 NOAA HSSD) and is determined by a ratio of uncertainty to allowable error. It is calculated as such:

$TVU\, QC _{(OCS Quality Metrics\hspace{1mm})} = Uncertainty / A + (B * Depth)$