Do we still need the Well Known Scale Set?

[joanma747]

Now that we have Common TMSs in Annex D and we want to encourage people to use them, do we still need he WKSS concept in annex C?. The link to a WKSS is just informative as the actual values fro the scales are repeated in any TMS.

After discussing it in telco 2021-02-25 we still believe they provide connection to the old WMTS and can still be included.

We will include a paragraph to explain that WKSS this was included fro interoperability but now the good practice is use common TMSs and TMSLimits if necessary.

[joanma747]

The following text has been added and modified in the section defining the WKSS:

When overlaying and presenting together tiles encoded in different tile matrix sets that do not have common sets of scale denominators and the same CRS in an integrated client, rescaling or re-projecting tiles to the common scale of the view might require re-sampling calculations that result in visual quality degradation.

The recommended way to prevent this problem is make use of the same global tile matrix sets, for example, one of the avialable in <>. If the coverage of the data covers only a part of the tile matrix set area, The tile matrix limits that can be used to inform about this limitations.

If using the same tile matrix set is not possible, using a common coordinate reference system and a common set of scales shared by as many layers and services as possible can also be a solution. Thus, the concept of well-known scale set (WKSS) is introduced.

Note that a WKSS only defines a small subset of what is needed to completely define a Tile Matrix Set. A WKSS is an optional feature that does not replace the need to define the Tile Matrix Set and its Tile Matrices. The original purpose of WKSS is no longer necessary if services share and reference common Tile Matrix Sets definitions such as the ones in <>.