[Qgis-user] SUM line lengths - QGIS 1.7.4

[Zoltan Szecsei]

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


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Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
P.O. Box 7, Muizenberg 7950, South Africa.

65 Main Road, Muizenberg 7945
Western Cape, South Africa.

34° 6'16.35"S 18°28'5.62"E

Tel: +27-21-7884897  Mobile: +27-83-6004028
Fax: +27-86-6115323     www.geograph.co.za
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