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iho-ohi / S-102-Product-Specification

It is opened to develop S-102 Bathymetric Surface Product Specification. The contents of this repository are not offical publication in force, therefore please check the final version on the IHO website.
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Possible Superfluous Value in Root Group Attributes #117

Closed hasel001 closed 4 months ago

hasel001 commented 4 months ago

Table Root Group Attributes (Section entitled Data Product Format, etc., which Metanorma numbers 11), Row Vertical Coordinate System, Column Remarks states (in relevant part):

Allowed values: 6498 (Depth—​metres—​orientation down) 6499 (Height—​metres—​orientation up)

My understanding is that we only ever allow the convention of positive down (i.e., 6498).

Am I missing something, or is it okay to delete the line listing 6499 as an option (and to change values to value)?

RohdeBSH commented 4 months ago

Yes, a tiny detail. If you choose the S-100 code 24 (Local Datum) for verticalDatum, the orientation of the Z-axis can be different from 6498 (orientation down).

Example: If I use the German standard height system (DHHN2016), I would set the attributes as follows: verticalCS = 6499 (orientation up) verticalDatumReference = 1 (s100VerticalDatum) verticalDatum = 24 (Local Datum)

hasel001 commented 4 months ago

By allowing the choice of a system whose convention is orientation down, we seem to be creating a conflict.

  1. In the paragraph directly following Figure - S-102 Grid point location, it says "Drying heights (drying soundings) are indicated by a negative depth value." The implication, in that case, is an orientation down configuration.

  2. Table Root Group Attributes, Row Vertical Coordinate System, Column Remarks states (in relevant part):

Allowed values: 6498 (Depth—​metres—​orientation down) 6499 (Height—​metres—​orientation up)

  1. Table BathymetryCoverage feature attribute parameters (in final table of annex), Row 4 says, "Drying heights (drying depths) are indicated by a negative value.

If (2) only allows 6498, (1) and (3) present no conflict. However, if (2) allows both, (1) and (3) will need to be rewritten to say something like: "Drying heights are indicated by having the opposite sign with respect to depths."

Do I infer correctly that (1) and (3) need to be changed in that way?

RohdeBSH commented 4 months ago

You're right, it does lead to a conflict.

Just prohibiting it on the side now also feels wrong somehow. The attribute "Depth" is defined in the IHO registry as "The vertical distance from a given water level to the bottom.". So this fits both 6498 (Depth-metres-orientation down) and 6499 (Height-metres-orientation up). However, the value range is limited from -14.0 to 11050.0. This means that if you specify 6499 (Height-metres-orientation up), you can only map water areas up to a depth of 14.0m. That is also nonsense. So it only makes sense to remove the 6499 (Height-metres-orientation up).

By the way. In comparison with the IHO registry, the "lower bound" and "upper bound" of Group_F are incorrect for the depth. That should be "lower"=-14 and "upper"=11050, right?

rmalyankar commented 4 months ago

An alternative is to update the constraints in the registry.

hasel001 commented 4 months ago

I apologize that I hadn't seen @rmalyankar 's comment before I committed my edits. However, I think it makes sense to modify ours rather than theirs. People should not be using S-102 to navigate more than 14 meters above the surface of the water or lower than the Challenger Deep. Regardless, I have made the changes here. Thank you both for your help!