[Qgis-user] QGIS project with no projection

[Jonathan Moules]

Hi Simon,
If you know the real-world width and height of the area covered on the image, could you not geo-reference it to have lower-left at 0,0, and then the top-right at the applicable location in the projection of your choice, and then work from there?

The problem is picking an applicable projection. I can't see any generic "X,Y" projection, let alone one that is suited to equal-area or equal-distance in the projections list. They may exist, I'm just failing to find them. They all seem to assume they're "somewhere" in the world (which can be a problem if the data is spatial but not geographical).
Personally if it's a relatively small area (a few km across), I'd probably just use a standard Mercator for the applicable part of the world probably.

Cheers,
Jonathan



---- On Fri, 06 May 2016 13:33:47 +0100 simonc8<simoncrombie at onetel.com> wrote ---- 

I want to use QGIS to make measurements such as distances and angles on a
flat scaled image which I have as a georeferenced tiff. I don't want to use
any projection - just a straightforward orthogonal linear scale in metres.
QGIS seems to require that I choose a projection. What would be the best
choice for my needs? Can I make a custom projection with no ellipsoid or
datum?

If I import my geotiff and don't specify a projection QGIS assumes my units
are in degrees rather than metres, which will make measurement of distances
and angles inaccurate.

Grateful for assistance. 



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