[Qgis-user] Question on Area in QGIS 2.18.13

[Randal Hale]

I have a question - this didn't seem to be an issue until 2.18.12 QGIS. 
I'm currently on 2.18.13 Ubuntu 17.04. I could be missing something.

I have a forestry client and they were preparing to do some aerial 
spraying. So I outlined the area to be sprayed and generated acres. 
Generally I set my project properties to feet (for units) and square 
feet (for area) and the ellipsoid set to none/planimetric. My data is 
stored in WGS84 in postgis. I pulled it out into a shapefile and 
eventually stored it in geopackage while trying to track down my issue.

Dropbox link to the data: 
https://www.dropbox.com/sh/8w1spcxu5by7z70/AACilL5kOeOC7tzX4WCEkOdka?dl=0

I set the CRS to EPSG:2274 - the data is in wgs84.

If I run acres  with project properties set to feet, square feet, and 
none/planimetric and using the Field Calculator I get: 372.82 acres. 
This is wrong.

If I run acres with project properties set to feet, square feet, and 
wgs84 as the ellipsoid I get 307.41 acres which appears to be right.

If I run acres using the virtual layer abilities: /select 
sum(st_area(st_transform(geometry,2274))/43560) from spray/ I get 306.04 
acres which may be right.

I didn't notice this until 2.18.12 - I updated to 2.18.13 and it is 
still acting "odd" - I didn't notice in 2.18.11 but I'm not sure if I 
ran any area calculations in 2.18.11. I have also noticed that if I 
switch from wgs84 (feet, square feet, none for ellipsoid in the project 
properties) and then switch to EPSG:2274 the ellipsoid changes to 
grs1980(iugg 1980)...... which having the ellipsoid at GRS80 may have 
been covering for my area calculations and making them "about right".

Anyway thoughts? Ideas? Am I doing something wrong?

Randy



  --
Randal Hale
North River Geographic Systems, Inc
rjhale at northrivergeographic.com
(423) 653-3611
https://www.northrivergeographic.com

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