We’d Like to Put Your Data on a Nautical Chart

If you are considering performing a hydrographic survey and are willing to share the data with us, we can pass it on to the UK Hydrographic Office to help them compile new or updated nautical charts and so help improve safety for mariners.

Your survey does not need to be carried out to full charting standards to be of use. Even without a full search for dangers, a modern survey can improve on our knowledge of the seabed. There will be no legal liability on you for the way that we use your data.

Some advice on how to help us to get the best out of your survey follows below. But even if you are unsure about these requirements, we would still like to receive a copy of your survey. It may reveal changes that should be shown on the chart as a “less water reported” legend, and/or may lead to a full survey being carried out.

The Maritime & Coastguard Agency are always happy to give help and advice on hydrographic data gathering requirements in order to increase the usefulness of hydrographic survey data.

Just a few minor changes to how your data is gathered and presented can make it much more useful for charting action…

The absolute basic information that we need is:

• A copy of your final survey drawing and/or final digital dataset. The digital data may be in a simple ASCII “xyz” (latitude, longitude, depth OR grid E, grid N, depth) format. The drawing can be in hard copy, but we would prefer a CAD (.dwg) file if at all possible.
• If the data has been passed through a gridding or binning process to produce the final drawing or dataset, then a copy of the pre-gridding dataset is required. Gridding and some binning techniques may cause the shoal depths to be lost.
• A note of the horizontal datum to which the positions are referred (or the grid, if appropriate).
• A note of the tidal datum to which the depths have been reduced.

The soundings should be reduced using observed tides (not predicted tides from Tide Tables).

This basic level of data will enable UKHO to accurately position the data and adjust the depths as necessary to chart datum.

To ensure that your data is fully usable, we also need:

Spurious data to be cleaned from the dataset.

Noise typically generates false shoal depths, and the surveyor is in the best position to determine which apparently shoal features are real and which are not. It can be misleading to pass false shoal depths through to the final chart – in order to avoid such a feature, a vessel may have to follow a course which is more dangerous than necessary. So if you can arrange to remove spurious features from the data, it will remove a lot of uncertainty when it is processed by UK Hydrographic Office.

What We Would Really Like:

It is desirable if as many of the following can also be achieved:

• All data should be rendered in digital form. Ideally, this should be in one of the following formats: Caris HDCS directory (i.e. “HIPS”); Simrad PROC directory, Generic Sensor Format or Fledermaus PFM; but simple ASCII “xyz” is acceptable if the other formats are not available.
• If a hard copy plot and/or .dwg drawing is available, please also supply that, as it helps UKHO to check that the digital data is complete Drawings may also include useful non-bathymetric detail, such as coastline and details of construction projects. Please record any differences between the digital data and the drawing, especially if depths on the drawing have been edited, but the edits have not been applied to the digital data.
• Cleaned digital data should have rejected soundings included, but flagged as deleted. The method used in any data-cleaning (e.g. Shoal or Median Biased) should be clearly stated.
• Digital data should be full density (i.e. prior to any gridding, binning or tinning being applied).

Ideally, the accuracy of both the depth and position of soundings should meet IHO S44 Order 1 requirements.Ideally, the density of the data should be such that the minimum target sizes stated in IHO S44 Order 1 are always detected.A report should describe how the data was gathered and processed.

It is particularly useful if the report can include:

• A list of the equipment and software used, and the personnel involved.
• How positioning equipment was set up and used
• How the echo-sounder transducer was set up and levelled

How tides were measured, how the tide pole or tide gauge was levelled and how depths were reduced to chart datum. NB a levelling diagram is a useful method of confirming that datum adjustments have been carried out correctly.

What Would be Totally Perfect:

• Reports written in the Royal Navy “Electronic Report of Survey” Microsoft Word template would be ideal (template available on request)

Data which fully complies with all aspects of IHO S44 Order 1 would be ideal.

If you require any assistance in making your data available for charting use, please contact the MCA at:

navigationsafety@mcga.gov.uk