[Qgis-us-user] New to QGIS and Spatial analysis

karsten karsten at terragis.net
Mon Mar 14 22:43:11 PDT 2022

actually when I think about it - it seems that you really can just use the
Model designer 
and use the 3 step in there I initially mentioned - that should work because
using the 
"Rectangles, ovals, diamonds" tool you indeed can already create the 1mi²
buffer ...


From: Qgis-us-user [mailto:qgis-us-user-bounces at lists.osgeo.org] On Behalf
Of karsten
Sent: Monday, March 14, 2022 22:38
To: 'Mike Seskin'; qgis-us-user at lists.osgeo.org
Subject: Re: [Qgis-us-user] New to QGIS and Spatial analysis

Hi Michael,
 >>> Yes, a couple of follow-up questions if you don't mind.is there a way
to automatically define a 1 square mile extent around each point in my shape
You could do that in multiple ways. 
Possibly the easiest would  be if you just used a circular buffer around
each  point and then calculated back from the circle area you would want the
buffer to contain using the a mathematical circle area calc. Such as 1km² =
π * r²  -> resolve by r. You could also use miles . However keep in mind
that this exact area  will depend on the map projection and associated map
units used.  So if your map projection units are in meters you will  need to
use those for the the conversion- 
However with naturally more difficult to use units (such as feet and miles)
a conversion is necessary anyways :)

So overall using the circular buffer radius would give you potential cut
shape. Now the problem is that raster (not really) can be cut by circular
shapes (well it works kind of visually at least), but a raster is
rectangular feature, however can contain NULL values for values outside a
cut line.
Another way would be to calculate the edge points of a 1mi² square that you
then create around the point as a center  - it could e.g. involve a python
script that you can use with the python console in QGIS ...
e.g. https://www.qgistutorials.com/en/docs/processing_python_scripts.html
Maybe there is a ready made tool out there where someone has done something
similar that can be reused, but so far I am not ware of one ...
Now there is also an option to sue a buffer with miter join style to create
a rectangular buffer . Here I am not sure what the buffer distance exactly
would be maybe try it out to get to 1mi² but you can do trial runs to get
near that desired area size 
>>> And then can I run the "convert map to raster" tool automatically on
each area.  So for instance if I have a shape file with 10 points layered on
Google satellite, can I use the "convert map to raster" to automatically
create 10 satellite image files? 
You can do that and it would involve the Model designer in QGIS. You can
create a model for reuse and add that to the processing tools ..
e.g. see
and here https://www.youtube.com/watch?v=eZb5VLTc9-o.




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