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I want to work with a planar coordinate system, and as far as I know QGIS automatically puts me in a cartesian plan if I don't set up a CRS (Coordinate Reference System) for my project. That is exactly what I want.

The issue (may) begin when I import the raster image that I want to work with: it asks me to set a CRS for the image. The same happens when I create a vector layer for drawing features over my raster image: it asks me for a CRS for the vector too. The project remains without a CRS, but untill now I can not put any raster or vector without an CRS.

For tests purposes I set up EPSG:32722 - WGS 84 / UTM zone 22S as the CRS for both raster and vector. I used UTM because I know it is based on a cartesian plan (though I'm not sure it's the best to do).

My goal is to draw some polygons and calculate the area of that polygons. The scale is obtained from my raster (there's an object with known size in the image).

I can't measure correctly the size of my object without setting the CRS of the project to be the same of the raster and vector, so I set the CRS of the project from the layer.

It looks like the area is being correctly measured, but I can't know for sure if some transformation is going on.

That said, my questions are:

Is there a way to import raster or create vector layers without a CRS (am I missing something)?

Are my areas being calculated correctly this way?

Is alright to use UTM for this purpose or there is a better option (maybe define a custom CRS)?

(sorry for my bad English)

QGIS 2.2.0 64 bits on Win 7 64 bits

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In the GIS world, it is intended that all layers must have a Coordinate reference system (CRS). Without that, the application has no idea how to put various data sources together.

Usually, Raster images have a CRS stored inside. If not, you have to georeference it using known points inside the raster and coordinates form another source. A common way is to load Google or Openstreetmap background with the Openlayers plugin, and georeference on that.

Once your raster is georeferenced, you can create a new vector layer, and digitize the features you want from the raster.

For calculating areas, UTM is surely a good choice.

  • Thanks for the reply, actually my image is not from a geographic location, it is an object which I want to get the area from, and the area will be in cm². I am using QGIS because I know a little bit of it and it is the software that I have now in hands, probably there are other softwares better suited for this work. I use a lot of OpenLayers (awesome plugin, btw) and I know how to georreference images, but unfortunately that's not the case here. Glad to know that UTM is a good choice! – elde0618 Apr 14 '14 at 19:23

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