When you initially load the NIS with S-57 datasets, you will likely be left with multiple representations of the same real-world feature in the geodatabase. For example, if you import three overlapping S-57 datasets (1:40,000, 1:100,000, and 1:500,000) into the NIS, you could end up with three features, one at each compilation scale, that represent the same real-world buoy.
You have a couple of options for dealing with multiple representations of the same real-world point geometry:
- Retain all real-world representations of the same feature in the NIS.
- Conflate two or more representations of the same real-world feature into a single feature in the NIS and reuse that single feature for multiple products at multiple scales.
The first approach, retaining multiple copies of the same feature, requires no preparatory work. However, as data is maintained over time, an easy change must be repeated for each representation of the feature at multiple scales, such as the color or shape of a buoy.
The second approach, conflating copies of the same real-world object into a single feature, does require preparatory work, but is more efficient over time, as an edit would only have to be performed once and it will be reflected in each product in which that feature participates.
Conflating the features in NIS
You can conflate simple or structure-equipment features and adjust their values and selection.
Example 1: Simple conflation
An example of this simple conflation is a wreck that appears on three scale products (1:10,000, 1:80,000, and 1:250,000). You could conflate the three wreck features, retaining the 1:10,000 feature. The conflated wreck feature gets a new PLTS_COMP_SCALE value of 250,000, and IS_CONFLATE is set to True.
Example 2: Conflation with a relationship
If a feature participates in a structure-equipment relationship, there are additional factors to consider. The decision to conflate must be consistent. If you decide to conflate the structure, you must also conflate the equipment. For example, you might have a wreck (DangersP/WRECKS) that appears with a light (AidsToNavigationP/LIGHTS) on three scale products (1:10,000, 1:80,000, and 1:250,000). You could conflate the three wreck features, retaining the 1:10,000 feature, and also conflate the three light features, retaining the 1:10,000 feature. The conflated wreck and light features both get a new PLTS_COMP_SCALE value of 250,000, and IS_CONFLATE is set to True. This allows the three products to show the conflated wreck and light once populated and updated.
What if the same wreck appeared without the light on a 1:500,000 scale product? You would handle this situation by giving the wreck feature a PLTS_COMP_SCALE value of 500,000 while the light feature still gets a value of 250,000. This means that when the 1:500,000 scale product is populated or updated, it shows the wreck but not the light.
- Identify the set of features that represent a single real-world feature.
- Decide which subset of those features you want to conflate.
If you have four candidate features, you can conflate two, three, or all four. If you choose to conflate less than the full set, the features you choose must be consecutive in the list of scales. For example, if you have four features (40K, 100K, 250K, and 500K) and choose to conflate two of them, you can conflate the 40K and 100K features, or 100K and 250K, or 250K and 500K. You cannot conflate the 40K and 250K features and retain the 100K feature as well.
- Determine which of those features has the best geometry.
Typically, this is the feature with the largest compilation scale. For example, a scale of 1:10,000 is greater than 1:250,000. This is the record you retain.
- Compare the attributes of the features to be conflated and, if you find significant differences, edit the feature you retain to correct all its attributes on the Attributes dialog box.
- In the retained feature, set the PLTS_COMP_SCALE value to the scale of the smallest scale (largest denominator) product on which the conflated feature should appear.
For example, if the conflated feature is to appear on products ranging from 1:10,000 to 1:250,000, change the PLTS_COMP_SCALE value from 10,000 to 250,000.
- In the retained feature, set the IS_CONFLATE value to True.
This attribute is used in the extraction queries and replica definitions to indicate this feature has been conflated with features from other scale bands, and it pertains to products in other scale bands.
- Delete the remaining features.