[GRASS-dev] Re: terminology issues in grass7

[Markus GRASS]

Michael Barton wrote:
>
>
> On Jun 16, 2009, at 12:39 PM, Paul Kelly wrote:
>
>> On Tue, 16 Jun 2009, Michael Barton wrote:
>>
>>> In GRASS, displaying Layer 1 will show all objects for some vector
>>> topologies, and only ID 1 and 2 for other topologies. However, by
>>> putting
>>> values into cat for Layer 1, you can also display ID's 3 & 4 for
>>> Layer 1. You
>>> can achieve the same effect by querying cat = 1 for Layer 2. The
>>> difference
>>> is that sometimes empty cats are displayed and sometimes they are
>>> not. To me
>>> this is kind of an automatic (inadvertent even) query. Some of this
>>> is only
>>> semantics, but I think we all agree that semantics can be important.
>>
>> IMHO these are all side-effects of the inconsistent way layers are
>> handled
>> amongst different GRASS modules. It's an implementation problem (perhaps
>> caused by confusion among developers as options were added and modified
>> over the years), rather than a fundamental problem with the layer
>> concept.
>
> The inconsistent implementation is an issue certainly. I don't think
> that there is a problem with underlying concept of the layer feature.
> Indeed, it is a very powerful data management feature of GRASS. I just
> think that another name for the feature would help users to understand
> and make use of it better--especially since we also use the term
> layers in the GUI layer manager to refer to superimposed displays of
> distinct geospatial data files, a very common usage in GIS.
You may notice that you have to specify a vector layer for d.vect in the
GUI layer manager, i.e. the GUI layer manager displays a vector layer
unless layer=-1. I bet you yourself use most of the time d.vect layer=1
and not layer=-1.
>
>>
>> If we manage to come to a full understanding of the capabilities and
>> possibilities of the concept of vector layers in GRASS (which I feel
>> this
>> discussion is really helping us to work towards, for me anyway), then it
>> would be an exciting project to do an audit of all vector modules and
>> the
>> way they handle layers, and tidy up all the inconsistencies so that the
>> meaning of layers is much more obvious, simply from the module
>> options and
>> flags. Perhaps too radical though.
Tidying up inconsistencies is not radical but regular maintenance work IMHO.

Markus