[Qgis-user] NewbieQ: Measurement tool weirdness?

[Goyo]

2011/3/9 Dan Lyke <danlyke at flutterby.com>:
> I'm running QGIS compiled from Subversion this morning, with support
> libraries as provided by Ubuntu 10.10. I'm having a bit of trouble
> figuring out the measuring tool. Short version: To get numbers that
> seem to make sense I have to click of "Ellipsoidal", and then get what
> look like right numbers in feet, but they're labeled "degrees".

Which projection are you using for the project? I get the correct
numbers in meters using the same projection as in the layer (EPSG:
2226).

r15395M from qgis.org repo in Ubuntu 10.10, which otoh is doing lots
of weird things like speaking to me in english and not opening old
projects.

Goyo

>
> Long version follows:
>
> I downloaded the "Parcels" shapefile data from
> https://gis.sonoma-county.org/catalog.asp
>
> Empty project, added PAR_PARCELS.shp as a layer. Right click on the
> layer, search for APN 008-454-003 (my house), click the "Zoom to
> Selection" icon.
>
> Select the line measurement tool, measure the front side of my lot, get
> 273.71km (it should be 52 feet, or 15.85 meters). Okay, I've clearly
> got a projection issue. Open up the Layer Properties box, see:
>
>   -  * Generated CRS (+proj=lcc +lat_1=38.33333333333334
>  +lat_2=39.83333333333334 +lat_0=37.66666666666666 +lon_0=-122
>  +x_0=2000000 +y_0=500000.0000000001 +ellps=GRS80 +datum=NAD83
>  +to_meter=0.3048006096012192 +no_defs)
>
> Which to my untutored eye seems right (ie: the lat and lon numbers
> aren't completely whack). But I can try "Specify CRS", and I put in
>
>  NAD83/California zone 2 (ftUS) EPSG:2226 208
>
> (EPSG:2226 is what looks right when I manipulate this data with other
> tools, like Python and Mapnik). Now it seems to be measuring 269.101km.
> And the back of the lot (the assessor's office tells me this is
> rectangular) measures 5,781.169km.
>
> If I click off the "Ellipsoidal" check box then I get a number that's
> closer to what I expect, but it's labeled "degrees".
>
> Can anyone point me to what I should be reading to explain this?
>
> Thanks.
>
> Dan
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