Format translator development

[David D Gray]

Hi Rich

Rich Shepard wrote:
> 
>   ... The MapInfo export format for points and lines is
> straight-forward: for points, the position and the symbol descriptor; for
> lines, the number of segments in the line then the position for each node.
> The MapInfo region (everyone else's polygon) is a closed line with one or
> multiple segments. What's interesting, of course, is that MapInfo does not
> build or maintain topology. For soil polygons, for example, each soil type
> is its own polygon and the common lines aren't, there's one line for each
> polygon.
> 

from this description it doesn't sound like GRASS, so I think some kind
of 
pre-processing in necessary.

> 
>   Now that I think about it, I agree. I need to understand the arc-node data
> structure's relationship to a closed polygon before I can write the
> MapInfo-to-GRASS translator.

The definition of a '2d-manifold' as defined in the SDTS spec,
part1.pdf, p13
and the discussion leading up to that, is a good description of GRASS's
structural requirements for polygon data, though there must be no
hanging
lines in a vector map. I doubt GRASS is based on this standard but it
seems to apply.

http://mcmcweb.er.usgs.gov/sdts/standard.html

> Of course, if you or anyone else with more
> experience in GRASS formats is willing to undertake this task, I'll be happy
> to relinguish it. But, I will certainly answer any questions regarding the
> MapInfo format.

That is a possibility, though there are doubtless many vector formats
we might want to import eventually, and it is best if those folk most
familiar with the source application handle the data transfer modules.
Perhaps you could send me a pointer to the relevant mif/mid spec, which 
would give me a better idea of how trivial or else difficult this task 
might be. 

David