[Qgis-user] Decoration Grid / drawing tools

[Patrick Dunford]

Hi, thanks for reply.

I have attached a screenshot that I hope will be small enough to be 
accepted by the list server. So the aerial photo background I am tracing 
from is not shown in it to save file size.

As you can see there is an irregularly shaped building to the left that 
I haven't actually traced in this case, I managed to find a layer of 
buildings that I could download for this particular area that have 
already been digitised by someone else or some computer program. As you 
can see, this building isn't nicely aligned to the grid.

I presume this software (Qgis) was designed by cartographers who have 
put in all these interesting looking tools that can do all sorts of 
stuff that I don't have much understanding of, and possibly in there 
somewhere might be something that can do this a lot easier than I have 
tried so far.

There are the useful rectangles and circles tools which are for drawing 
regular shapes (you can see several examples of regular shapes in this 
screenshot that were drawn with this tool) but aren't particularly 
designed, as far as I can tell, for something that looks more like the 
building on the left which is a number of rectangles joined together. 
Anyway if I was wanting to digitise a building like the one on the left 
my instinct would be to have some way of aligning it to the grid, but it 
actually can't be made to achieve this because it's a few degrees off 
and unless the canvas background can be rotated independently of the 
grid, or the grid, I don't seem to have a way to get a grid alignment.

So the best I can work out of how to digitise this shape is being able 
to align to the grid in some way perhaps with some kind of snapping to 
the grid or alignment to the grid or being able to see the angles on 
each corner or whatever. I am not sure how to achieve that at the moment.

Thanks

On 29/01/24 19:31, Andrea Giudiceandrea via QGIS-User wrote:
>> Patrick Dunford enzedrailmaps at gmail.com
>> Sun Jan 28 13:45:24 PST 2024
>
>> I note there is a canvas grid that can be turned on by going to View 
>> -> Decorations -> Grid. However the rotation of this appears to be 
>> fixed to north/south/east/west 
>
> Hi Patrick,
> the grid is a coordinates grid in the map's coordinate reference 
> system, so it is obviously always north-south/east-west oriented 
> (acually, X/Y oriented in the map CRS's Cartesian plane) based on the 
> map's coordinate reference system north-south/east-west directions 
> (actually, X/Y directions in the map CRS's Cartesian plane).
>
>> and does not appear to have any provision to be changed in rotation 
>> in any form, such as for example aligning to the four sides of the 
>> window.
>
> May you please elaborate? Since the grid is a coordinates grid in the 
> map's coordinate reference system and normally the axes directions of 
> the map are aligned to the four sides of the map window, then the grid 
> should always be aligned to the four side of the map window, unless 
> you have set a rotation angle for the map and thus both the map and 
> the grid are rotated and the axes directions of both the map and the 
> grid are no more aligned with the four side of the map window.
>
>> Second issue is drawing tools. When I am tracing building outlines I 
>> want to be able to draw exact right angles with the sides of the 
>> building,
>
> You can use the Advanced Digitizing panel, provided your map's CRS is 
> a projected CRS.
>
> Best regards.
>
> Andrea
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