[Qgis-user] SUM line lengths - QGIS 1.7.4

[Nathan Woodrow]

You can use the method that I outline here:

http://woostuff.wordpress.com/2011/02/23/total-length-of-selected-objects-qgis-via-python/

- Nathan

On Wed, Jun 20, 2012 at 8:14 PM, Zoltan Szecsei <zoltans at geograph.co.za> wrote:
> Hi,
> I've opened a DGN file of contours, and would like to calculate the sum of
> the lengths of all the contours.
>
> Using Vector->Analysis Tools->Sum Line Lengths  is totally counter intuitive
> (OK, for me!).
>
> Why do I have to have a polygon in order to sum line lengths - In SHAPE file
> methodology those geometries are even in separate files!
> And then to create a new poly layer in order to see the calculated value
> seems kind of arb.
> Is the polygon perimeter also added to the calculated length?
>
> If said polygon is purely for creating a selection subset of the
> line-lengths to be summed, then why not use the selection tool instead?
>
> When querying an individual line, its length is shown as a derived field. If
> there was a way to put derived fields into the attribute tables, then at
> least that column could be summed.
>
> Anyway, it seems like I have missed the point of summing line lengths in
> this way, so please can someone enlighten me why this methodology is useful.
>
> Thanks & regards,
> Zoltan
>
>
> --
>
> ===========================================
> Zoltan Szecsei PrGISc [PGP0031]
> Geograph (Pty) Ltd.
> P.O. Box 7, Muizenberg 7950, South Africa.
>
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>
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