[GRASS5] line types

[rgrmill at rt66.com]

Radim wrote:

> Of course, all modules missing boundary type needs that option.
> If you add that option, please commit also to cvs for other users.

Done.  The necessary changes are nearly trivial. I'm new with CVS so it 
will take more time to figure out how to commit the changes then it took 
to make the changes.

I suspect that there are a couple reported bugs that may be caused by 
the line/area edge distinction.

> I don't understand why you cannot not do the task with type=edge,
> why you must remove 'line' type.

I can and did.  But I regard that as a hack -- adding an unnecessary 
complication to support a model that I disagree with.

> Yes, but we are talking about the cases, where separation is not 
effective.

The reason for fixing v.llabel and v.extract was to make separation more 
effective.  Fixes to a few other modules would help in the same regard.

> I think that build process works without errors, i am interested in 
clean 
> data sets, for which build process fails - please send to me if 
possible.
> I care about error messages, and i need to know if error is realy 
error
> in area topology and not correct free end of line.


What do you regard as a clean data set?  If you mean one for which the 
build reports no errors then we have a logical problem.  v.transform has 
always reported errors doing builds.  Some errors may not even be 
reported.  It is more of a problem to me that GRASS offers no good tool 
for finding and fixing the problems.


> I don't understend why you must do that. If you like, you can use edge 
type 
> for all arcs. We must keep possibility to do that, for those who 
want.
>
> In general, you can use edge type only, if you want, in system with 
both
> edge/line type, but others who need the distinction, cannot use the 
system
> where line type is not present.

I use the edge type when I can, but it isn't always possible.  For 
instance, US Census Bureau Tiger County Line data are broken down into 
line objects and area object.  I don't believe I have an option of 
importing roads (typed as line objects) as area edges.  In fact, most of 
the GRASS import packages do not give one the choice of line type.  That 
means that for dxf data and for many important public data sources 
(USGS, NRCS and US Census, for instance) I have to accept whatever line 
type the import package decides to set.

The the only way you can get data that is consistent with the GRASS 
line/area edge distinction is to digitize it in GRASS.  And you can only 
reasonably manipulate that distinction if you're working with small data 
sets.  That is very limiting.  It isn't even very well supported in 
GRASS.

The line/area edge distinctions causes a lot more problems then it has 
has advantages, and in every case where there appears to be a use for 
the difference there also appears to be a workable alternative.  All 
things considered I think we need to get rid of the distinction.


Roger Miller