[Qgis-us-user] Question on area calculations

[Randal Hale]

This has me puzzled. So I may have screwed up a very large job with 
incorrect acres and I was doing what I thought I needed to be doing. I'm 
probably doing this wrong - but if I'm doing this wrong there's a large 
chance more people are doing the same.

This is all in QGIS 3.0.1

I have a forester who is working on a tract of land. There was a very 
hurried cruise they needed to do.

Data is in WGS84 and set to EPSG:2240 in QGIS.

Change the ellipsoid to None under project properties:

  * using the identify button are 237 acres.
  * I get roughly 194 acres with the measure tool

Changing the ellipsoid to GRS1980 (which QGIS Defaults to):

  * I get 196 acres with the identify tool.
  *   I use the measure tool I get 194 acres

I am assuming the 194/196 measurements are the exact same and due to 
human error on my part. PostGIS gives me 196 acres.

I guess (as I type this out) my correct course of action should be to 
leave the ellipsoid in GRS1980 and do my work - BUT - I thought I could 
drop back to none/planimetric if I set the projection to EPSG:2240 in QGIS.

Can anyone clue me in - I'm preparing for much yelling from the client 
in about 15 minutes as I was off about 40 acres which was a costly 
mistake. I'm not confident currently in my area measurements using QGIS 
and I need to get confident.

Randy





-- 
Randal Hale
rjhale at northrivergeographic.com
https://www.northrivergeographic.com
(423)653-3611

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