[GRASS5] line types

[Radim Blazek]

On Wednesday 10 April 2002 07:08 pm, rgrmill at rt66.com wrote:

> 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.  

Clean data fulfil "6.7 Vector Topology Rules" in Programmer's Manual.

> v.transform has always reported errors doing builds.

Vector without errors had errors after v.transform?

> Some errors may not even be reported.  

Which errors are not reported.

> It is more of a problem to me that GRASS offers no good tool
> for finding and fixing the problems.

That is also problem for me, and that is challenge for future. It is not 
simple task, David can talk about that.

> 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.  

So they use a model with edge/line distinction?

> 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.

There are v.line2area and v.area2line - scripts based on v.out/in.ascii, I 
want to write v.type working on binary files. It is true that import modules 
are usually missing that option and I know that it is useful (v.in.dgn has 
type= option for example).

> 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.

You can get consitent data to GRASS, what you only need, is to sort
lines and edges during the import. Is it problem to run?:
v.in.dxf lines=rivers type=line
v.in.dxf lines=lakes type=edge
(Of course if type= was available, now with v.line2area following the later)

> 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.

What is an alternative for example with forests, fields and roads in my last 
mail?

Radim