Loss of scale after clipping

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Loss of scale after clipping

David Addy
I am finding that after clipping a raster the resulting clipped file has no
scale. Or rather the scale says 0:1 and stays at 0:1 whatever the zoom
level.
This persists for all the map, whatever layers are on or off.
Can anyone help, please?
I am running 3.8.3 on Widows 10.



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Re: Loss of scale after clipping

Mike Flannigan

I could easily be wrong, but I say I (and you) cannot
clip a raster layer.  In the clip box the selections
for "Input layer" do not include raster layers.

QGIS 3.2.0 - Win7.



Mike


On 10/4/2019 7:00 AM, [hidden email] wrote:
> I am finding that after clipping a raster the resulting clipped file has no
> scale. Or rather the scale says 0:1 and stays at 0:1 whatever the zoom
> level.
> This persists for all the map, whatever layers are on or off.
> Can anyone help, please?
> I am running 3.8.3 on Widows 10.


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Re: Loss of scale after clipping

David Addy
I have clipped rasters and vector files many times before with no problems.
Go to Raster/Extraction/Clip raster by mask layer.
The mask layer is something I draw.
 IE Make new vector polygon, add feature and then draw a box around the area
I want to include in my clip.



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Re: Loss of scale after clipping

David Addy
Nicolas Cadieux messaged me as follows:
"Could this just be a GUI thing?   Try closing QGIS and opening the file in
a new empty project.
Nicolas ."

I replied as follows:
"Hi Nicolas,
I have done what you said. Although it is a bit laborious to load everything
into a new project, it does seem to have worked.
So thanks very much for that advice.
I wonder what action set it off though?
Best wishes and many thanks,
David"

I thought I would post this exchange so everyone else can get the benefit of
this work around.




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Re: Loss of scale after clipping

David Addy
This scale problem has just raised its head again in a different context.
I have been experiencing the 40 second loading time which a few other people
have also reported, ever since 3.4.1, when this all started.
In addition I often get QGIS not responding messages most often when
clicking on "Project" tab to do a save or whatever. I have got used to
waiting 20 seconds for it to become responsive again.
I have carried on just accepting these delays, and the occasional crash when
closing.
Last night it crashed when closing and today I can open the map but the
scale bar shows the dreaded 0:1 and it is impossible to change it.
I am on W10 with version 3.8.3 of QGIS, which I always load using the
standalone installer.
I have tried uninstalling  every earlier QGIS versions, disabling all my
plugins, using a different profile, and none of these has had any effect
upon the slow loading speed etc.
I think all these symptoms are linked in some way, and I blame it all on
QGIS 3.4.1. Has it left something lurking somewhere?



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Re: Loss of scale after clipping

David Addy
Oh Dear, I have just tried to follow the tip from Nicolas above about
reloading files into a new empty project.
This time this does not work.
I have just loaded a county outline and a coastal line with default styling
and the scale bar still says 0:1.
Now What?
Any ideas?
Regards to all.
NB QGIS 3 would be really magic without all this stuff.



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Re: Loss of scale after clipping

Nick Hopton
Just a thought. A friend upgraded recently and some of his settings didn't
carry over, it was a CRS problem. Perhaps just check that the default system
CRS, the project CRS and the CRS of each layer is set correctly before
clipping.  



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Re: Loss of scale after clipping

David Addy
Hi Nick,
I thought you were onto something with that suggestion of incompatible CRS
settings.
The coastal file that I had clipped came from a MapInfo source and the CRS
was interpreted by QGIS as a custom CRS rather than as EPSG 27700. Although
the MapInfo CRS was meant to be the GB National Grid.
So I changed its CRS to 27700 and clipped it again.
This loaded up fine and I got the correct scale in the box at the bottom of
the map window.
Thinking all was well I saved the project and closed it.
However, when I came to open it again this morning the map looked correct
but the scale had reverted to 0:1.
Now I am completely baffled.



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Re: Loss of scale after clipping

Nick Hopton
Hi David, it just had the ring of a possible CRS problem. If you'd care to
email the raster image and the clipping layer I'll try it here, you have my
email address I think. N.



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