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

Mike Seskin Seskin_Michael_X at solarturbines.com
Tue Mar 15 06:58:16 PDT 2022

Hi karsten - thanks again for all these tips, the graphical modeler tutorial was an excellent "discovery"!!

Mike Seskin | EQL
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From: karsten <karsten at terragis.net>
Sent: Monday, March 14, 2022 10:43 PM
To: 'karsten' <karsten at terragis.net>; Mike Seskin <Seskin_Michael_X at solarturbines.com>; qgis-us-user at lists.osgeo.org
Subject: RE: [Qgis-us-user] New to QGIS and Spatial analysis

This is a message from karsten at terragis.net<mailto:karsten at terragis.net>.
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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<mailto: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 file?
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<https://urldefense.com/v3/__https:/www.qgistutorials.com/en/docs/processing_python_scripts.html__;!!M7dyoZOwuwF45AU!jTzfzhkUd3m7Qhmk3Tmz2G6s14fiNWqQ8rJXUz1gbZM_QuYBxR7N-7NshB92_SHk63GvCLg2Ars$>
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 https://docs.qgis.org/3.22/en/docs/user_manual/processing/modeler.html?highlight=model%20designer
<https://urldefense.com/v3/__https:/docs.qgis.org/3.22/en/docs/user_manual/processing/modeler.html?highlight=model*20designer__;JQ!!M7dyoZOwuwF45AU!jTzfzhkUd3m7Qhmk3Tmz2G6s14fiNWqQ8rJXUz1gbZM_QuYBxR7N-7NshB92_SHk63GvG5NAYok$>and here https://www.youtube.com/watch?v=eZb5VLTc9-o<https://urldefense.com/v3/__https:/www.youtube.com/watch?v=eZb5VLTc9-o__;!!M7dyoZOwuwF45AU!jTzfzhkUd3m7Qhmk3Tmz2G6s14fiNWqQ8rJXUz1gbZM_QuYBxR7N-7NshB92_SHk63GvC8EywMg$>.


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