when is the overscale pattern shown?

[kusala9]

Current draft of S-98 Annex C has the following content:

NOTE:   If the display is compiled from more than one ENC of the same optimumDisplayScale, and if the mariner deliberately chooses 
to zoom in so that the display scale exceeds the maximumDisplayScale, then only the "overscale indication" must be shown. The 
"overscale pattern" (area fill OVERSC01) must not be shown. 

this is based on the following S-52 clause (I believe):

the content of the Note box is the issue - what does "deliberately chooses to zoom in" mean? Does this mean the overscale pattern is only shown for those datasets which are rendered in order to fill the screen (which we could specify as part of the algorithm) ? It's unclear, and it is also unclear whether anyone has actually implemented this as there is no explicit test for it in S-64.

Options are:

• Leave text in as is
• Change text to only require the overscale pattern for datasets used to fill the screen (by referencing the branch in the algorithm where this happens
• Take out completely, thus overscale pattern is used whenever datasets are drawn larger than maximumDisplayScale

Additionally, an explicit test could be added to S-164 for this condition.

[kusala9]

this is from SelectDataCoverages in the select/display algorithm. I believe if we restricted the overscale to data coverages which are selected after line 3.b is reached this might work??

[benhazelgrove]

AHO will implement maximumDisplayScale at 2x optimumDisplayScale in order to replicate the understanding that S-57 ECDIS displays overscale pattern (jailbars) at 2x compilation scale. This is based on the DCEG (Clause 3.5.1 specifically refers to this functionality).

My understanding was that the only time this wouldn't occur is when the cell is the largest scale product (nothing larger exists) and the mariner zooms past maximumDisplayScale, only the overscale indication would be shown.

[kusala9]

I had a discussion with richard fowle over the phone on this today. He confirmed his understanding of the requirement as written in S-52 is the same. The mariner shouldn't see jail bars over the "largest scale" data even if it's zoomed in past 2x compilation scale, presumably to avoid cluttering the screen. However, he also wasn't sure most current S-57 ECDIS implement this feature, with many just switching on the prison bars on all data which is > x2 zoomed. Also confirmed there's no specific test on this at the moment so it's likely current implementation will be variable.

[MikusRL]

The text in C-15.1.2.1 is with the "optimumDS". @kusala9 You have it in the v.1.7.2 (from GitHub) in this form: The citation in the first comment is outdated...

If as stated in v 1.7.2, I think then it makes sense, that "prison bars", if they need to come on, they come on only after passing the set by the Producer maximumDS. So then at any scenario, over the optimumDS only indication of the overscale is on the screen. This I think is the closest to the "expected to be implemented" S-57 performance currently, and in the scenario where the prisonbars are expected, these arenot brought up right after the optimumDS, if the Producer has not set purpously the maximumDS value the same as the optimumDS. In the conversion Guidance there is the "automated" suggestion that maximumDS should be converted to 2X as the S-57ns comp scale.

It is my understanding that this was the point that some HOs wanted to have the saying when the prison bars, if expected, to come on on their products. And was the outcome of the S-101PT meeting discussions in Indonesia and Sweden.