search

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.
Other
28 stars 11 forks source link

Possible Superfluous Value in Root Group Attributes #117

Closed hasel001 closed 2 months ago

hasel001 commented 2 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 2 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 2 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 2 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 2 months ago

An alternative is to update the constraints in the registry.

hasel001 commented 2 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!