[Qgis-user] Bathymetry data area coverage calculator

[Peters]

Thanks, I'll check it out.

On Sat, Jul 31, 2021, 20:42 Charles Dixon-Paver <charles at kartoza.com> wrote:

> The raster calculator is a tool for raster analysis which doesn't quite
> suit your needs as I understand them. If you want to learn how to use the
> raster calculator there is a tutorial available on the QGIS changelog
> lessons [1].
>
> That blog post I linked to before is likely the most effective or
> performant option for you, and it contains links to scripts that will
> perform the analysis for you.
>
> As an alternative, I have created a simple model which steps through the
> vectorization process of reclassifying a raster and calculating the area
> [2]. The data I used to test the model was the SRTM tile used in the
> previously mentioned lesson [1], so you can introspect it and copy the
> logic or tweak it as needed. I did a session on using the modeler for the
> last Open Day [3] so you can get familiar with them if you aren't already.
>
> [1] https://changelog.qgis.org/en/qgis/lesson/raster-16/detail/51/?q=7.2
> [2]
> https://github.com/zacharlie/effective-dollop/blob/main/qgis-models/raster_area_calculation_example.model3
> [3] https://github.com/qgis/QGIS/wiki/QOD-July-2021
>
> On Sat, 31 Jul 2021 at 20:29, Peters <petersinmorocco at gmail.com> wrote:
>
>> Very helpful. Yes, our data is raster. I saw a calculator tool in the
>> raster toolbar but haven't been able to figure it out or if it's pertinent.
>>
>> On Sat, Jul 31, 2021, 19:01 Charles Dixon-Paver <charles at kartoza.com>
>> wrote:
>>
>>> I think you will need to provide more information on describing the
>>> input data, as well as how exactly you wish to process it.
>>>
>>> If your coverage data is vector areas you should be able to simply use
>>> the aggregate processing tool using $area as the source expression and
>>> stipulate a sum aggregate function. You may also use the grouping
>>> function to filter the results as needed using an expression.
>>>
>>> This would provide the area based on map units, so you would need to
>>> reproject your data into a relevant metric projection before performing the
>>> aggregation. A single hectare is simply 10000 m² so simple arithmetic will
>>> allow you to convert metric areas to hectares.
>>>
>>> If your data is another vector data type such as point clouds, you may
>>> need to buffer or calculate a minimum bounding geometry or convex hull
>>> before processing it as the area calculation will of course only work on
>>> area features.
>>>
>>> For raster data, the total area would be a simple calculation of the
>>> extents, or the dimensions and cell size. Again, you may need to reproject
>>> the data for it to be available in meters.
>>>
>>> If, however, you wish to segregate raster data based on cell value, you
>>> may want to recode and vectorize the data, or alternatively perform some
>>> form of custom analysis as described in the following article:
>>> https://www.kartoza.com/en/blog/calculating-area-of-rasters-in-qgis/
>>>
>>> Regards
>>>
>>> On Sat, 31 Jul 2021 at 19:15, Peters <petersinmorocco at gmail.com> wrote:
>>>
>>>> Does anyone know of such a calculator as a plugin or option?  At the
>>>> moment I am using QGIS app. Our client has asked for area coverage in sq.
>>>> mtrs or hectares. Appreciate any info you may have.
>>>>
>>>> --
>>>> *regards,*
>>>> *K. Peters*
>>>>
>>>> *cell: (Morocco) +212.671.218606*
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>>>
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