[GRASS-user] Extracting line heights from 3d vectors

[Nick Cahill]

Dear Hamish,

Yes, the lines are absolutely horizontal - every point has the same  
elevation. I tried v.to.db before writing to the list. But v.to.db  
only has options to upload the following values: cat, area, compact,  
perimeter, length, count, coor, start, end, sides, query, slope. A  
v.what query on a typical line has:

Map: con10
Mapset: PERMANENT
Type: Line
Line: 2110
Length: 432.740896
Line height: 200.000000
Layer: 1
Category: 2110

Driver: mysql
Database: sardisutm
Table: con10
Key column: cat
cat : 2110
type : 4
level : 3
graphicgroup : 0
colorindex : 3
weight : 0
style : 0
entitynum :
mslink :
text :

I tried just typing "line height" into v.to.db anyway, but got a  
predictable error

ERROR: value <line height> out of range for parameter <option>
        Legal range:  
cat,area,compact,perimeter,length,count,coor,start,end,sides,query,slope

I just figured out that you can get the information from v.out.ascii,  
and then discard the coordinates and such; but it seems like there  
should be an easier way of accessing this information.

Many thanks!

Nick Cahill



On Nov 28, 2008, at 7:14 PM, Hamish wrote:

> Nick wrote:
>> I have a series of contour vector maps imported from a CAD
>> program (Microstation). The CAD maps were in 3d, and the 3d
>> information was successfully imported into GRASS, so the
>> vectors have line heights as well as length, etc. Now I need
>> to export these into shapefiles. When I do this, all the
>> other useless CAD data like line color, style, weight, etc.
>> is exported as attributes in the .dbf file, but line height
>> is not -- it is not a field in the mySQL database but is
>> part of the geometry of the line, if I understand what's
>> going on here correctly. Is there a way to transfer line
>> height into the attribute table so I can access and export
>> it? Many thanks,
>
> v.db.addcol + v.to.db ?
>
> note that unless lines are perfectly horizontal (eg elevation  
> contours)
> you can not assign a single elevation value to a line's attributes (as
> each vertex will have its own value, and the attribute is associated  
> with
> the line as a whole), so I would expect in general for it to refuse  
> to try.
>
> as for 3D shapefile export, ummm... check the wiki, help pages, and ML
> archives. It rings a bell but I've no idea how.
>
>
> Hamish
>
>
>
>
>