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Dynamic Decluttering

The Problem

Intersecting symbols cluttering the display impair the readability of a chart display. During the production of an ENC cell, sounding labels are placed at fixed positions in such a way that the cell looks clear and visually appealing and provides the desired information density. The chart display shows this desired appearance only at the particular compilation scale that the cartographer or chart production software had in mind. When zooming out the sounding labels move closer together, clutter the chart display and finally render the chart display unreadable.

 

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The image shows unevenly distributed soundings. The sounding labels intersect only in some areas, most of them are readable.

 

Software applications displaying ENC cells suppress the sounding labels at a roughly estimated minimum scale to prevent clutter. Typically the scale at which the sounding labels disappear will be estimated from the compilation scale which is contained in the cell’s metadata.

This approach is not a satisfactory solution for a number of reasons:

  • The minimum scale for suppressing sounding labels can only be roughly estimated. Besides the distribution of the soundings the symbol size used for the sounding labels is a second important parameter. If the suppression scale is too large, that means when zooming out the sounding labels are shown too long, the soundings clutter the chart display. If, to make sure to avoid clutter, the suppression scale is chosen smaller than necessary the valuable information of the sounding values is not displayed although the labels do not intersect at all or only a few do.
  • Some cells unfortunately have regions with very different sounding value densities. In this case no single sounding label suppression scale is appropriate for the cell.
  • The chart display of ENC data is usually composed of a number of cells. As the estimated scale at which sounding labels intersect is different for each cell at the contact line of two neighbored cells there are sharp visual contrasts where sounding labels are displayed for one cell but suppressed for the other cell. If systems seek to avoid such a situation by suppressing the sounding labels at one scale for all cells in the chart display the result will be quite inadequate for most cells at certain scale ranges.
  • Suppressing all sounding labels at once at a certain scale is especially distracting during smooth zoom operations where the user reasonably expects continuous changes of the chart display. Additionally when zooming out smoothly it would also be confusing to see elements disappear from the chart display for no apparent reason.

 

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The above image illustrates the traditional measure to prevent clutter - to hide all sounding labels. A lot of valuable depth information is lost although most of the sounding labels had been readable. Note that the sounding labels would be already suppressed at a larger scale as descibed in the text.

 

Our Solution: Dynamic Decluttering

When zooming out smoothly the charting engine Despina hides sounding labels immediately before they intersect others. To ensure safety the sounding label representing the shallower depth is always shown, the one representing the greater depth is suppressed. For two soundings of the same depth the selection is random.

Unlike the smooth fading in and out for the text labels, the color of sounding labels is not altered because showing labels with transparency could lead to a situation where a shallow sounding label can be mistakenly confused with a deep sounding which should of course be avoided.

The same technique is used for contour labels.

Dynamic Decluttering allows us to show smooth zoom operations and camera flights during which the chart display adapts continuously to the changing scale. The end user does not get distracted as the chart display does not change unexpectedly or abruptly but is instead consistent over time.

 

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Dynamic Decluttering: Only those sounding labels are suppressed which would otherwise intersect with another sounding label representing a shallower depth.

 

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This image shows the same chart display at a smaller scale. The visual appearance is very constant for all scales and the chart display stays readable all the time through Dynamic Decluttering.

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