[Qgis-user] Area Calculation in Field Calculation

Jeremy Hill hije14 at gmail.com
Fri Jul 6 09:44:15 PDT 2012



------------------------------

Message: 4
Date: Fri, 6 Jul 2012 15:16:09 +0530
From: Harish <harry.om2000 at gmail.com>
To: Qgis-user at lists.osgeo.org
Subject: [Qgis-user] Area calculation in field calculator
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<CAKCjEX9Vt_0jvEEiHSMOVGMGRR3wMb-0e6BHiZHmrqnB_4Z_=Q at mail.gmail.com>
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1-
I converted projection 4326 to 32643(UTM zone 43N) to get are calculation.
I used geometry operator as $area with creating a new field of decimal
(real) type with width 10 and 2 precision. I tried with different widths
and precisions, every time there are 7-8 digits after decimal, like,
2361773.81506348
2895003.41503906
1384160.6237793
10020411.4874268

ANSWER1----- You need to uncheck the "Toggle Editing" and "save" your layer 
and then it will be displayed with the proper width and precision that you 
set it to.


2
Further I read in new functionality list of QGIS1.8 that area/length etc.
may be calculated by using project (if in metric units) CRS in QGIS 1.8,
without changing original CRS of layer if it is in Geographic coordinates.
Is this feature available in 1.8?

ANSWER2---  It does give you the option that when you use "Export/Add 
Geometry Column" that it gives you the option to Calculate using Layer CRS, 
Project CRS, or Ellipsoid. You can save to a new layer or update the current 
one which your using. I have not experimented with this in different 
projections to verify the accurate data or the area/length but the "plugin" 
does work.

Regards

OS-Windows7, QGIS 1.8 stand alone

-- 
Harish Kumar Solanki, Assistant Professor
National Institute of Rural Development (NIRD),
Ministry of Rural Development, Government of India
Jaipur, Rajasthan, India- Pin-302006
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