Quantcast

Re: Area Calculation in Field Calculation

classic Classic list List threaded Threaded
4 messages Options
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Area Calculation in Field Calculation

Jeremy Hill


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

Message: 4
Date: Fri, 6 Jul 2012 15:16:09 +0530
From: Harish <[hidden email]>
To: [hidden email]
Subject: [Qgis-user] Area calculation in field calculator
Message-ID:
<CAKCjEX9Vt_0jvEEiHSMOVGMGRR3wMb-0e6BHiZHmrqnB_4Z_=[hidden email]>
Content-Type: text/plain; charset="iso-8859-1"

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.osgeo.org/pipermail/qgis-user/attachments/20120706/e47b31f2/attachment-0001.html>


_______________________________________________
Qgis-user mailing list
[hidden email]
http://lists.osgeo.org/mailman/listinfo/qgis-user
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Area Calculation in Field Calculation

Jeremy Hill
Harish,
As my screen capture shows, I am able to select the Layer or Project or Ellipsoid CRS. I am able to do it on a “Line” “Point” and “Polygon” Shapefile (.shp) file. I’m running QGIS 1.8 Lisboa. Maybe check and make sure that you have the most up-to-date version. Apart from that I’m not sure what else to tell you. Hopefully someone else can help.
Jeremy
 
Sent: Sunday, July 08, 2012 12:59 AM
Subject: Re: [Qgis-user] Area Calculation in Field Calculation
 
Thanks! point one is solved but for point two, export/add geometry tool returns the window as attached, there is no option for choosing CRS for area calculation.

Regards

On Fri, Jul 6, 2012 at 10:14 PM, Jeremy Hill <[hidden email]> wrote:


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

Message: 4
Date: Fri, 6 Jul 2012 15:16:09 +0530
From: Harish <[hidden email]>
To: [hidden email]
Subject: [Qgis-user] Area calculation in field calculator
Message-ID:
<CAKCjEX9Vt_0jvEEiHSMOVGMGRR3wMb-0e6BHiZHmrqnB_4Z_=[hidden email]>
Content-Type: text/plain; charset="iso-8859-1"

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
 

_______________________________________________
Qgis-user mailing list
[hidden email]
http://lists.osgeo.org/mailman/listinfo/qgis-user

Export-add geometry in QGIS 1.8.jpg (37K) Download Attachment
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: Area Calculation in Field Calculation

hksolanki
Yes I was a problem of version. I was using 1.8 on a system where 1.7.4 was also installed and probably plugin did not update itself with installation of 1.8. When I installed 1.8 on a machine which doesn't have any version of QGIS, it showed correct window.

Thanks
Harish
On Sun, Jul 8, 2012 at 1:49 PM, Jeremy Hill <[hidden email]> wrote:
Harish,
As my screen capture shows, I am able to select the Layer or Project or Ellipsoid CRS. I am able to do it on a “Line” “Point” and “Polygon” Shapefile (.shp) file. I’m running QGIS 1.8 Lisboa. Maybe check and make sure that you have the most up-to-date version. Apart from that I’m not sure what else to tell you. Hopefully someone else can help.
Jeremy
 
Sent: Sunday, July 08, 2012 12:59 AM
Subject: Re: [Qgis-user] Area Calculation in Field Calculation
 
Thanks! point one is solved but for point two, export/add geometry tool returns the window as attached, there is no option for choosing CRS for area calculation.

Regards

On Fri, Jul 6, 2012 at 10:14 PM, Jeremy Hill <[hidden email]> wrote:


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

Message: 4
Date: Fri, 6 Jul 2012 15:16:09 +0530
From: Harish <[hidden email]>
To: [hidden email]
Subject: [Qgis-user] Area calculation in field calculator
Message-ID:
<CAKCjEX9Vt_0jvEEiHSMOVGMGRR3wMb-0e6BHiZHmrqnB_4Z_=[hidden email]>
Content-Type: text/plain; charset="iso-8859-1"

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

Email- [hidden email], [hidden email],
Tele-Fax-0141-2209905, Mo.- 09214446732, 09414291732
Website-  http://www.nird.org.in, http://watershed.rajasthan.gov.in/
LinkedIn: www.linkedIn.com/in/hksolanki


_______________________________________________
Qgis-user mailing list
[hidden email]
http://lists.osgeo.org/mailman/listinfo/qgis-user
Reply | Threaded
Open this post in threaded view
|  
Report Content as Inappropriate

Re: digitizing new shapefile lAYERS

mikec
In reply to this post by Jeremy Hill
everytime i digitizine while snapping to my outer boundary my new
shapefile does not appear, but when i digitize my new shapefile while
not snapping to any other files it does appear, and then i can alter
that shape by snapping the nodes to the files i want it snapped to.  
this sounds ridiculous how you have to trick the software into creating
a shapefile that can be viewed.  Why can i not view a digitized shape
when snapping?  I know i can use the polygonizer, but i have made it
this far and not willing to alter my method.
_______________________________________________
Qgis-user mailing list
[hidden email]
http://lists.osgeo.org/mailman/listinfo/qgis-user
Loading...