[Qgis-user] Calculate acres

[Garth Fletcher]

The file "gcp_list.txt" contains 160 POINTS, not polygons, thus $area 
would be meaningless...

If using NAD83 / UTM zone 19N (EPSG:26919) they plot as 17 points 
roughly 110 miles SE of Pamlico Sound in an area roughly 700 m X 700 m.

Each mapped "point" actually contains several (average of 10) 
overlapping points sharing the same coords.

You actually should be using UTM zone 18N to avoid negative X values, 
though that doesn't really matter here.

By the way if you substitute column headers for the "+proj=tmerc..." 
first line, use

Lo19_Lon ∆ lat ∆ elevation ∆ GCP_Pixel ∆ coords ∆ photo ∆ number
    where " ∆ " indicates a TAB

That way your columns can be named when you import the data as delimited 
text

Cordially,
Garth Fletcher

On 2/15/25 3:24 AM, hans at hanskingsrs.com wrote:
> Hi Craig
>
> Here is a sample CRS file
>
> Lo19 Lon Lat elevation GCP pixel coords photo number
>
>
> With best
>
> H
> -----Original Message-----
> From: QGIS-User <qgis-user-bounces at lists.osgeo.org> On Behalf Of Garth
> Fletcher via QGIS-User
> Sent: Saturday, 15 February 2025 07:43
> To: qgis-user at lists.osgeo.org
> Subject: Re: [Qgis-user] QGIS-User Digest, Vol 228, Issue 27
>
> Is the layer CRS a projected CRS, e.g., with units of feet?
> If a geographical CRS, such as WGS84, measured in degrees Lat/Long it won't
> work.
>
> Also, does the layer include at least 1 polygon?  If not then you'll see
> "NULL".
> But I've never seen "nan" in that context.
>
> I've used the approach you describe many times.
>
> Garth Fletcher
>
> On 2/14/25 Marc Bordelon <marcbordelon at yahoo.com> wrote
>> Subject: [Qgis-user] Calculate acres
>>
>> I've created a shape file, geometry is polygon, I have the CRS set as
>> what the project is set at.I open the field calculator-Create a new
>> field "Acres" - set the Output field type to "Decimal number (real) -
>> output field length to 5 and precision to 2 - using the Geometry-
>> expression: $area to calculate the acres it gives me "nan" for the
>> preview. No acres.I've been able to create a new field and calculate
>> acres and length (ft) with no problem.?
>> I'm running qgis 3.34.7
>> MarcBordelonmarcbordelon at yahoo.com
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