[Qgis-user] SUM line lengths - QGIS 1.7.4

[Zoltan Szecsei]

Thanks to both Leyan and Nathan for their contribution, but it would be 
really nice if someone could shed  light on the workings and efficacy of 
using

*Vector->Analysis Tools->Sum Line Lengths*

Thanks,
Zoltan


On 2012/06/20 12:37, Nathan Woodrow wrote:
> 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.

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

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Tel: +27-21-7884897  Mobile: +27-83-6004028
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