[Qgis-developer] Raster calc syntax

[John Donovan]

One way of hiding some of the syntactic complexity might be to use one
of the visual workflow systems like Orange http://orange.biolab.si/ to
construct raster operations, especially if it somehow tied in with the
SAGA/Grass/etc. workflow stuff that's being developed. True, this is
not an insignificant amount of work, but if all it did was generate
valid rastercalc expressions, then it can sit on top of the current
system rather than replace it.

Alternatively, how about categorising operators like the expression
builder in a spreadsheet?

Something else that might be useful is a preview window for the raster
calculator. I got bitten by a similar issue to Tim, where I wanted to
invert the values in my raster. I used:
-myraster at 1
Which is a valid expression, but returned 0 for all values. Instead I
had to use:
-(myraster at 1)

This wasted 20 minutes on my very large dataset. In hindsight I should
have done in the first place what I did in the end, and tested it with
a subset of my big raster, but a small thumbnail like some of the Gimp
plug-ins have would have saved me some time.

-John

On 26 January 2012 10:43, Marco Hugentobler
<marco.hugentobler at sourcepole.ch> wrote:
> Hi Nathan
>
>
>>One question, how needed is the Min X, Max Y etc stuff.  Currently it takes
>> up a lot of room and clutters (IMO) the interface.  I was thinking we might
>> be able to hide it in an >advanced section if it is only used rarely.
>
> IMO, you could move those element into an advanced section. It is important
> to have the possibility to set the output resolution, but not a setting you
> need fast access to.
>
> Regards,
> Marco
>
>
> On 26.01.2012 01:15, Nathan Woodrow wrote:
>
> Hey Paolo,
>
> I stated working on adding the expression builder widget last night, didn't
> get very far as I had to do some other things.
>
> One question, how needed is the Min X, Max Y etc stuff.  Currently it takes
> up a lot of room and clutters (IMO) the interface.  I was thinking we might
> be able to hide it in an advanced section if it is only used rarely.
>
> - Nathan
>
> On Thu, Jan 26, 2012 at 4:13 AM, Paolo Cavallini <cavallini at faunalia.it>
> wrote:
>>
>> Hi all.
>> How about simplifying the syntax of raster calc? If even Tim can get
>> wrong:
>>
>> http://linfiniti.com/2012/01/simple-binary-raster-reclassification-in-qgis/
>> this means that the average user will be in trouble.
>> Am I wrong?
>> Of course, using the expression widget now used for field calc and for
>> labelling
>> would probably solve the issue.
>> All the best.
>> --
>> Paolo Cavallini - Faunalia
>> www.faunalia.eu
>> Full contact details at www.faunalia.eu/pc
>> _______________________________________________
>> Qgis-developer mailing list
>> Qgis-developer at lists.osgeo.org
>> http://lists.osgeo.org/mailman/listinfo/qgis-developer
>
>
>
>
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>
> --
> Dr. Marco Hugentobler
> Sourcepole -  Linux & Open Source Solutions
> Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
> marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> Technical Advisor QGIS Project Steering Committee
>
>
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