Missing Ranges

[Lukas Panneke]

I encountered a bug caused by missing RangeMin and RangeMax on MMSI fields.
So I checked what field types don't have range properties.

I think these must have range properties:

• MMSI
• TIME

I think these should have range properties:

• SPARE
• RESERVED
• BINARY

For these range properties don't make sense:

• STRING_LZ
• STRING_FIX
• STRING_LAU
• VARIABLE

All other field types have range properties set always.

[Lukas Panneke]

I want these range properties, because without them I need to have a function checking if a value is ERROR or UNKNOWN. With the recent discussion on the existence of ERROR, I would rather not have a custom function for that. I would like to just use a range check and take Canboats position on the issue.

Range properties are also valuable for writing N2k payloads. If I have range properties on a field, I can easily check if a value fits in the field. That is why I would welcome range properties even on fields where the semantics are uncertain. Even If I don't know what a number means, I want to know if it fits.

[Martti T.]

You probably should not check SPARE/RESERVED and BINARY fields. BINARY field could be longer than any number could hold and I think it is mostly used for fields which content is not known. RESERVED/SPARE are padding field, that act as "no value" and should have always same value (all bits 1 or 0).

There are comments about meaning/usage of these fields:

    {
        "Name":"RESERVED",
      "Description":"Reserved field",
      "EncodingDescription":"All reserved bits shall be 1",
      "Comment":"NMEA reserved for future expansion and/or to align next data on byte boundary"
      },

    {
        "Name":"SPARE",
      "Description":"Spare field",
      "EncodingDescription":"All spare bits shall be 0",
      "Comment":"This is like a reserved field but originates from other sources where unused fields shall be 0, like the AIS ITU-1371 standard."
      },

    {
        "Name":"BINARY",
      "Description":"Binary field",
      "EncodingDescription":"Unspecified content consisting of any number of bits."
      },

[Kees Verruijt]

This makes total sense. I just need to special case these as they have non obvious ranges.

[Kees Verruijt]

And yes, spare/reserved/binary fields will not get a range, imo this is undefined.