This document describes the HydrOffice QC Tools application (3.10). For the project page, go here.

2.2.4. Holiday Finder

2.2.4.1. How To Use?

Scan grids for unpopulated nodes (“holidays”).

  • Select the Holiday Finder tab (Fig. 2.19) on the bottom of the QC Tools interface.

  • In Parameters, turn the knob to select All holes, Object detection, or Full coverage, depending on the analysis you wish to run based on the coverage requirements of the survey (see How Does It Work?)

  • To change the Parameters for Holiday Finder v4:

    • Click the Unlock button, and click OK to the dialogue.

    • Set the Upper holiday area limit (as multiple of minimum holiday size). Unpopulated parts of the grid larger than this setting will not be flagged as holidays.

  • In Execution, click Holiday Finder v4.

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Fig. 2.19 The Holiday Finder tab.

  • After computing, the output window opens automatically, and the results are shown (Fig. 2.20).

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Fig. 2.20 The output message at the end of Holiday Finder v4 execution.

  • An output window will open in File Explorer. From the output window, drag-and-drop the desired output file into the processing software to guide the review.

Note

For proper visualization, the software adopted to analyze the S57 output of VALSOU Checks has to represent the sounding values in meters.



2.2.4.2. How Does It Work?

The grid is scanned, and any empty grid nodes (“holes”) surrounded by populated nodes are identified. These are flagged as holidays based on 2018 NOAA NOS Hydrographic Survey Specifications and Deliverables.

The specifications have different criteria by which holidays are defined based on coverage requirements:

  • A holiday under Object Detection coverage requirements is defined as collinear, contiguous unpopulated nodes sharing adjacent sides.

  • A holiday under Full Coverage requirements is defined as a box of unpopulated nodes.

  • There is also the option to simply flag all unpopulated nodes as holidays, by selecting the All holes setting.

The holiday size is calculated in number of nodes based on the minimum allowable resolution and the grid resolution, per this formula:

floor((minimum allowable resolution X 3) / grid resolution)

Only in the case of a variable resolution input, all the tiles are re-sampled to create a single resolution grid (selecting the highest resolution among all the grid tiles).

The minimum allowable resolution is determined based on the resolution pairing from the median value of all the node depths belonging to the holiday perimeter per the below tables (Fig. 2.21) for Object Detection Coverage and Complete Coverage as defined by NOAA Specifications.

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Fig. 2.21 NOAA specifications for object detection (left) and complete coverage (right) require multibeam surfaces to have the above grid-resolution thresholds as a function of depth range.

Note

The output of Holiday Finder is a sounding, with a value of “1” for certain holidays, and “2” for possible holidays.

The following images illustrate the outcomes of the three algorithms applied to a single-resolution grid (with the minimum allowable resolution equals to the grid resolution):

  • In the example in (Fig. 2.22), the All holes setting marks three holes of 12, 7, and 2 nodes.

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Fig. 2.22 Example for All holes.

  • In the example in (Fig. 2.23), Object Detection requirements identify the holes of 12 and 7 nodes, because each has 3 collinear, contiguous unpopulated nodes. The hole with 2 grids does not.

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Fig. 2.23 Example for Object detection.

  • In the example in (Fig. 2.24), Full Coverage requirements identify the hole of 12 grid nodes, because there it contains an instance of 3x3 unpopulated grid nodes. The holes with 7 and 2 nodes do not.

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Fig. 2.24 Example for Full coverage.

A candidate hole is flagged with a “1” (if certain) or a “2” (possible holiday).

Note that the default Upper holiday area limit (as multiple of minimum holiday size) is set to 1000, meaning that an unpopulated part of the grid will be flagged only if smaller than 1000 times the minimum holiday size. This setting exists so the search can be refined at the user’s discretion.

For example:

  • If desired to search for only the smallest of holidays, the Upper holiday area limit might be set at 100.

  • If desired to flag all unpopulated parts of the grid, regardless of their size, the Upper limit would be set at unlimited.

  • Settings in between are used at the discretion of the user, to identify holidays, while also preventing undue clutter in the output.



2.2.4.3. What do you get?

Upon completion of the execution of Holiday Finder you will receive a pop-up verification if your surface contains potential holidays or not (Fig. 2.25).

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Fig. 2.25 The output message at the end of Holiday Finder v4 execution.

Holiday Finder produces one .000 files containing the locations of potential holidays represented as soundings (Fig. 2.26). Certain holidays are represented with 1 and possible holidays are represented at 2.

fliers tab

Fig. 2.26 An example of a certain holiday identified with a sounding.

The naming convention of the output files contains important information about the settings that were used to execute Holiday Finder. Each setting is separated by a period in the naming convention. See Fig. 2.27.

naming convention for holiday finder output

Fig. 2.27 Example naming convention for a Holiday Finder output. In this example the user selected a Object Detection algorithm with an upper holiday limit of 1000.