date:20180117

Re: [Qgis-user] Qgis-user Digest, Vol 143, Issue 27

2018-01-17 Thread Chas Sheen

Thanks- problem solved.
Chas Sheeb

On 17 January 2018 at 22:43,  wrote:

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> Today's Topics:
>
>1. Re: Generating black white from RGB landsat   using   Raster Map
>   calculator? (Michel Stuyts)
>
>
> -- Forwarded message --
> From: Michel Stuyts 
> To: "qgis-user@lists.osgeo.org" 
> Cc:
> Bcc:
> Date: Wed, 17 Jan 2018 14:33:03 +
> Subject: Re: [Qgis-user] Generating black white from RGB landsat using
> Raster Map calculator?
>
> Chas,
>
>
>
> If I have a color GEOTIFF and I want to show or save it as a grayscale
> GEOTIFF, I use one of these 2 solutions. Depending on the control you want
> on the color to grayscale conversion it might also be a solution for you.
>
>
>
>
>
> Solution 1:
>
> If the only thing you want to do is show a colour geotiff in grayscale,
> you can just change the properties of the layer. In the layer properties
> you go to the tab “Style”. Under “Color rendering” you will find the option
> “Grayscale”. By default the option will be set to “Off”, but you can change
> it to turn grayscale on. Try one of the three options to see what fits your
> image best.  After that you can also change the values of “Brightness” or
> “Contrast” to get the best result.
>
>
>
> This way you won’t change anything in your source file and it won’t save a
> grayscale tiff, but it will just show your raster file as grayscale in QGIS.
>
>
>
> Solution 2:
>
> If you want to end up with a geotiff file that has the same information in
> grayscale I usually use some graphical software in the process, but for
> that you can’t use a GeoTiff, because you would loose the georeference
> information of the file. Therefore I use the following steps:
>
> 1.   Save your geotiff file as TIFF-file with a TFW file:
>
> a.   Right click on your source geotiff file in the layers panel.
>
> b.   Select Save As…
>
> c.   Select Rendered image as Output Mode
>
> d.   Select Gtiff as format
>
> e.   Deselect “Add saved file to map”
>
> f.Under “Create Options”  click on the + button to add an option.
> For the newly added option you have to type TFW as “Name” and YES as
> “Value” (double click in the newly created Option cell to type in it).
>
> g.   Click on the “Browse…” button to select a name and location for
> your grayscale TIFF file.
>
> h.   Click on the “OK” button
>
> 2.   Open the newly created TIFF file in graphical software like
> XnView, IrfanView or GIMP. Change the image in that software to grayscale
> and save the file.
>
> 3.   Add the newly created TIFF file back to QGIS
>
> 4.   Save your newly created TIFF file as a GeoTIFF file:
>
> a.   Right click on your newly created TIFF file in the layers panel.
>
> b.   Select Save As…
>
> c.   Select Rendered image as Output Mode
>
> d.   Select Gtiff as format
>
> e.   Click on the “Browse…” button to select a name and location for
> your grayscale GEOTIFF file.
>
> f.Click on the “OK” button
>
>
>
> Michel
>
>
>
>
>
>
>
>
>
> *Van:* Qgis-user [mailto:qgis-user-boun...@lists.osgeo.org] *Namens *Chas
> Sheen
> *Verzonden:* woensdag 17 januari 2018 14:33
> *Aan:* 'Micha Silver' ; qgis-user@lists.osgeo.org
> *Onderwerp:* Re: [Qgis-user] Generating black white from RGB landsat
> using Raster Map calculator?
>
>
>
> Mike,
>
> So everything in the capture below of the Raster calculator should work? I
> cannot find any output.
>
> I’m in Perth, Australia so home now and away from the office and QGIS, but
> would like to get it working tomorrow.
>
> How do apply a grayscale to a raster? As I said, I’m new to QGIS
>
> Chas Sheen
>
>
>
> *From:* Micha Silver [mailto:tsvi...@gmail.com]
> *Sent:* Wednesday, January 17, 2018 8:39 PM
> *To:* Chas Sheen ; qgis-user@lists.osgeo.org
> *Subject:* Re: [Qgis-user] Generating black white from RGB landsat using
> Raster Map calculator?
>
>
>
> Hello Chas
>
> On 01/17/2018 01:52 PM, Chas Sheen wrote:
>
> Richard,
>
>
>
> I should have made my initial query clearer.
>
> I am trying to output a black and white geotiff.
>
> It's still not clear what you are asking. AFAIK, there's no such thing as
> a "black and white geotiff". You can apply any color table you want to any
> raster. You can apply a gray scale to any of the landsat bands.
>
>
>
> If you are trying to create a new raster from

Re: [Qgis-user] Generating black white from RGB landsat using Raster Map calculator?

2018-01-17 Thread Michel Stuyts

Chas,

If I have a color GEOTIFF and I want to show or save it as a grayscale GEOTIFF, 
I use one of these 2 solutions. Depending on the control you want on the color 
to grayscale conversion it might also be a solution for you.


Solution 1:
If the only thing you want to do is show a colour geotiff in grayscale, you can 
just change the properties of the layer. In the layer properties you go to the 
tab “Style”. Under “Color rendering” you will find the option “Grayscale”. By 
default the option will be set to “Off”, but you can change it to turn 
grayscale on. Try one of the three options to see what fits your image best.  
After that you can also change the values of “Brightness” or “Contrast” to get 
the best result.

This way you won’t change anything in your source file and it won’t save a 
grayscale tiff, but it will just show your raster file as grayscale in QGIS.

Solution 2:
If you want to end up with a geotiff file that has the same information in 
grayscale I usually use some graphical software in the process, but for that 
you can’t use a GeoTiff, because you would loose the georeference information 
of the file. Therefore I use the following steps:

1.   Save your geotiff file as TIFF-file with a TFW file:

a.   Right click on your source geotiff file in the layers panel.

b.   Select Save As…

c.   Select Rendered image as Output Mode

d.   Select Gtiff as format

e.   Deselect “Add saved file to map”

f.Under “Create Options”  click on the + button to add an option. For 
the newly added option you have to type TFW as “Name” and YES as “Value” 
(double click in the newly created Option cell to type in it).

g.   Click on the “Browse…” button to select a name and location for your 
grayscale TIFF file.

h.   Click on the “OK” button

2.   Open the newly created TIFF file in graphical software like XnView, 
IrfanView or GIMP. Change the image in that software to grayscale and save the 
file.

3.   Add the newly created TIFF file back to QGIS

4.   Save your newly created TIFF file as a GeoTIFF file:

a.   Right click on your newly created TIFF file in the layers panel.

b.   Select Save As…

c.   Select Rendered image as Output Mode

d.   Select Gtiff as format

e.   Click on the “Browse…” button to select a name and location for your 
grayscale GEOTIFF file.

f.Click on the “OK” button

Michel




Van: Qgis-user [mailto:qgis-user-boun...@lists.osgeo.org] Namens Chas Sheen
Verzonden: woensdag 17 januari 2018 14:33
Aan: 'Micha Silver' ; qgis-user@lists.osgeo.org
Onderwerp: Re: [Qgis-user] Generating black white from RGB landsat using Raster 
Map calculator?

Mike,
So everything in the capture below of the Raster calculator should work? I 
cannot find any output.
I’m in Perth, Australia so home now and away from the office and QGIS, but 
would like to get it working tomorrow.
How do apply a grayscale to a raster? As I said, I’m new to QGIS
Chas Sheen

From: Micha Silver [mailto:tsvi...@gmail.com]
Sent: Wednesday, January 17, 2018 8:39 PM
To: Chas Sheen ; qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] Generating black white from RGB landsat using Raster 
Map calculator?

Hello Chas
On 01/17/2018 01:52 PM, Chas Sheen wrote:
Richard,

I should have made my initial query clearer.
I am trying to output a black and white geotiff.
It's still not clear what you are asking. AFAIK, there's no such thing as a 
"black and white geotiff". You can apply any color table you want to any 
raster. You can apply a gray scale to any of the landsat bands.

If you are trying to create a new raster from the three RGB bands using some 
expression, that should work. You can use either of three tools: the built in 
QGIS raster calculator, or thru the Processing toolbox there's SAGA Raster 
calculus and the GRASS module r.mapcalculator.

Again, none of this has anything to do with coloring. After running the raster 
calculator, you can color the result with a gray scale color table, a red color 
table, or any other color ramp you choose.


Have split the original (landsat) image into RGB images.
When I apply the expression in the capture below, and hit run, nothing is saved 
to the results directory.
I’m assuming that my expression or something else in the raster calculator is 
wrong?
The final product that I’m after is a xyz grid where z is the black-white 
amplitude…which I think should be relatively easy (?) once I have the 
black-white image.
After you running the calculator expression, then you can save the result in 
many formats, including gridded XYZ, ArcINFO ASCII, or many others, using the 
gdal_translate tool. This is under the Raster->Conversion menu.


Chas Sheen
0448017282

From: Richard McDonnell [mailto:richard.mcdonn...@opw.ie]
Sent: Wednesday, January 17, 2018 7:13 PM
To: Chas Sheen ;

Re: [Qgis-user] Generating black white from RGB landsat using Raster Map calculator?

2018-01-17 Thread Chas Sheen

Mike,

So everything in the capture below of the Raster calculator should work? I 
cannot find any output.

I’m in Perth, Australia so home now and away from the office and QGIS, but 
would like to get it working tomorrow.

How do apply a grayscale to a raster? As I said, I’m new to QGIS

Chas Sheen

 

From: Micha Silver [mailto:tsvi...@gmail.com] 
Sent: Wednesday, January 17, 2018 8:39 PM
To: Chas Sheen ; qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] Generating black white from RGB landsat using Raster 
Map calculator?

 

Hello Chas

On 01/17/2018 01:52 PM, Chas Sheen wrote:

Richard,

 

I should have made my initial query clearer.

I am trying to output a black and white geotiff.

It's still not clear what you are asking. AFAIK, there's no such thing as a 
"black and white geotiff". You can apply any color table you want to any 
raster. You can apply a gray scale to any of the landsat bands.

 

If you are trying to create a new raster from the three RGB bands using some 
expression, that should work. You can use either of three tools: the built in 
QGIS raster calculator, or thru the Processing toolbox there's SAGA Raster 
calculus and the GRASS module r.mapcalculator. 

 

Again, none of this has anything to do with coloring. After running the raster 
calculator, you can color the result with a gray scale color table, a red color 
table, or any other color ramp you choose.

 

 

Have split the original (landsat) image into RGB images.

When I apply the expression in the capture below, and hit run, nothing is saved 
to the results directory.

I’m assuming that my expression or something else in the raster calculator is 
wrong?

The final product that I’m after is a xyz grid where z is the black-white 
amplitude…which I think should be relatively easy (?) once I have the 
black-white image.

After you running the calculator expression, then you can save the result in 
many formats, including gridded XYZ, ArcINFO ASCII, or many others, using the 
gdal_translate tool. This is under the Raster->Conversion menu.

 

 

Chas Sheen

0448017282

 

From: Richard McDonnell [mailto:richard.mcdonn...@opw.ie] 
Sent: Wednesday, January 17, 2018 7:13 PM
To: Chas Sheen   ; 
qgis-user@lists.osgeo.org  
Subject: Re: [Qgis-user] Generating black white from RGB landsat using Raster 
Map calculator?

 

Chas,
Two options for splitting RGB into separate images in QGIS.

1.  Semi-Automatic Classification Plugin, Preprocessing, Split Raster Bands
2.  Grass r-rgb (Processing Toolbox)

Any one of these tools will split the Raster for you easy enough
Regards,

Richard

On 17/01/2018 00:48, Chas Sheen wrote:

I split the image into R, G, B

Worked out in QGIS wher the Raster map calculator is.

Run...several times

No result foud in Results Directory. It runs quickly then refreshes inputs and 
logs to blanks.

I'm new to QGISso have probably left out something basic.

Any clues

 









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-- 
Richard McDonnell
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OPW FRM Data Management
52 Stephens Green, Dublin 2.
TEL: 01 6476543

  



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Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918
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Re: [Qgis-user] Generating black white from RGB landsat using Raster Map calculator?

2018-01-17 Thread Richard McDonnell


Chas,
The only thing I can see wrong with your equation is the lack of Brackets
Try:

(R*0.2989)+(G*0.587)+(B*0.144)

See Does that help. you should also try the QGIS Raster Calculator, see 
if its an issue with the GRASS Plugin/Instillation.

Regards,

Richard

On 17/01/2018 11:52, Chas Sheen wrote:


Richard,

I should have made my initial query clearer.

I am trying to output a black and white geotiff.

Have split the original (landsat) image into RGB images.

When I apply the expression in the capture below, and hit run, nothing 
is saved to the results directory.


I’m assuming that my expression or something else in the raster 
calculator is wrong?


The final product that I’m after is a xyz grid where z is the 
black-white amplitude…which I think should be relatively easy (?) once 
I have the black-white image.


Chas Sheen

0448017282

*From:*Richard McDonnell [mailto:richard.mcdonn...@opw.ie]
*Sent:* Wednesday, January 17, 2018 7:13 PM
*To:* Chas Sheen ; qgis-user@lists.osgeo.org
*Subject:* Re: [Qgis-user] Generating black white from RGB landsat 
using Raster Map calculator?


Chas,
Two options for splitting RGB into separate images in QGIS.

 1. Semi-Automatic Classification Plugin, Preprocessing, Split Raster
Bands
 2. Grass r-rgb (Processing Toolbox)

Any one of these tools will split the Raster for you easy enough
Regards,

Richard

On 17/01/2018 00:48, Chas Sheen wrote:

I split the image into R, G, B

Worked out in QGIS wher the Raster map calculator is.

Run...several times

No result foud in Results Directory. It runs quickly then
refreshes inputs and logs to blanks.

I'm new to QGISso have probably left out something basic.

Any clues

Displaying image.png




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--
*_Richard McDonnell_*
*GIS Specialist PgD GIS AssocSCSI*
*OPW FRM Data Management*
*52 Stephens Green, Dublin 2.*
TEL: 01 6476543





Email Disclaimer: http://www.opw.ie/en/disclaimer/



--
*_Richard McDonnell_*
*GIS Specialist PgD GIS AssocSCSI*
*OPW FRM Data Management*
*52 Stephens Green, Dublin 2.*
TEL: 01 6476543
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Re: [Qgis-user] Generating black white from RGB landsat using Raster Map calculator?

2018-01-17 Thread Micha Silver


  
  
Hello Chas

On 01/17/2018 01:52 PM, Chas Sheen
  wrote:


  
  
  
  
  
Richard,
 
I should
have made my initial query clearer.
I am
trying to output a black and white geotiff.
  

It's still not clear what you are asking. AFAIK, there's no such
  thing as a "black and white geotiff". You can apply any color
  table you want to any raster. You can apply a gray scale to any of
  the landsat bands.


If you are trying to create a new raster from the three RGB bands
  using some _expression_, that should work. You can use either of
  three tools: the built in QGIS raster calculator, or thru the
  Processing toolbox there's SAGA Raster calculus and the GRASS
  module r.mapcalculator. 


Again, none of this has anything to do with coloring. After
  running the raster calculator, you can color the result with a
  gray scale color table, a red color table, or any other color ramp
  you choose.





  

Have
split the original (landsat) image into RGB images.
When I
apply the _expression_ in the capture below, and hit run,
nothing is saved to the results directory.
I’m
assuming that my _expression_ or something else in the raster
calculator is wrong?
The
final product that I’m after is a xyz grid where z is the
black-white amplitude…which I think should be relatively
easy (?) once I have the black-white image.
  

After you running the calculator _expression_, then you can save
  the result in many formats, including gridded XYZ, ArcINFO ASCII,
  or many others, using the gdal_translate tool. This is under the
  Raster->Conversion menu.



  

 

  Chas Sheen
  0448017282

 

  
From: Richard McDonnell
[mailto:richard.mcdonn...@opw.ie] 
Sent: Wednesday, January 17, 2018 7:13 PM
To: Chas Sheen ;
qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] Generating black white
from RGB landsat using Raster Map calculator?
  

 
Chas,
  Two options for splitting RGB into separate images in QGIS.

  Semi-Automatic Classification Plugin,
Preprocessing, Split Raster Bands
  Grass r-rgb (Processing Toolbox)

Any one of
  these tools will split the Raster for you easy enough
  Regards,
  
  Richard

  On 17/01/2018 00:48, Chas Sheen wrote:


  

  I split
  the image into R, G, B


  Worked
  out in QGIS wher the Raster map calculator is.


  Run...several
  times


  No
  result foud in Results Directory. It runs quickly then
  refreshes inputs and logs to blanks.


  I'm new
  to QGISso have probably left out something basic.


  Any
  clues


   


  

  
  



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  -- 
Richard McDonnell
GIS Specialist PgD GIS
AssocSCSI
OPW FRM Data Management
52 Stephens Green, Dublin
2.
TEL: 01 6476543



  
  Email Disclaimer: http://www.opw.ie/en/disclaimer/
  
  
  
  
  
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-- 
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Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918
  

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Re: [Qgis-user] Generating black white from RGB landsat using Raster Map calculator?

2018-01-17 Thread Chas Sheen

Richard,

 

I should have made my initial query clearer.

I am trying to output a black and white geotiff.

Have split the original (landsat) image into RGB images.

When I apply the expression in the capture below, and hit run, nothing is saved 
to the results directory.

I’m assuming that my expression or something else in the raster calculator is 
wrong?

The final product that I’m after is a xyz grid where z is the black-white 
amplitude…which I think should be relatively easy (?) once I have the 
black-white image.

 

Chas Sheen

0448017282

 

From: Richard McDonnell [mailto:richard.mcdonn...@opw.ie] 
Sent: Wednesday, January 17, 2018 7:13 PM
To: Chas Sheen ; qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] Generating black white from RGB landsat using Raster 
Map calculator?

 

Chas,
Two options for splitting RGB into separate images in QGIS.

1.  Semi-Automatic Classification Plugin, Preprocessing, Split Raster Bands
2.  Grass r-rgb (Processing Toolbox)

Any one of these tools will split the Raster for you easy enough
Regards,

Richard

On 17/01/2018 00:48, Chas Sheen wrote:

I split the image into R, G, B

Worked out in QGIS wher the Raster map calculator is.

Run...several times

No result foud in Results Directory. It runs quickly then refreshes inputs and 
logs to blanks.

I'm new to QGISso have probably left out something basic.

Any clues

 








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-- 
Richard McDonnell
GIS Specialist PgD GIS AssocSCSI
OPW FRM Data Management
52 Stephens Green, Dublin 2.
TEL: 01 6476543

  



Email Disclaimer: http://www.opw.ie/en/disclaimer/ 

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Re: [Qgis-user] Generating black white from RGB landsat using Raster Map calculator?

2018-01-17 Thread Richard McDonnell


Chas,
Two options for splitting RGB into separate images in QGIS.

1. Semi-Automatic Classification Plugin, Preprocessing, Split Raster Bands
2. Grass r-rgb (Processing Toolbox)

Any one of these tools will split the Raster for you easy enough
Regards,

Richard

On 17/01/2018 00:48, Chas Sheen wrote:

I split the image into R, G, B
Worked out in QGIS wher the Raster map calculator is.
Run...several times
No result foud in Results Directory. It runs quickly then refreshes 
inputs and logs to blanks.

I'm new to QGISso have probably left out something basic.
Any clues

Displaying image.png


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--
*_Richard McDonnell_*
*GIS Specialist PgD GIS AssocSCSI*
*OPW FRM Data Management*
*52 Stephens Green, Dublin 2.*
TEL: 01 6476543

OPW - Ag féachaint don am atá le teacht - Ag caomhnú ón am atá thart
OPW - Looking to the future - Caring for the past

***
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Re: [Qgis-user] Why does this message keeps occuring in QGIS? GEOS geoprocessing error: One or more input features have invalid geometry.

2018-01-17 Thread Martin Weis

Am 16.01.2018 um 21:05 schrieb David Shi:
> It is not merge.  I am trying to intersect two vector ShapeFiles.
> Each contains a collection of polygons.  Each collection of polygons
> cover the same geography, but has different boundaries. Can I do
> that?

Sounds like a classic intersect, did you try that already?
You get the combination of the two layers, if you have overlapping
polygons with different geometries, then all boundaries are kept and the
new polygons are bound by them (likely to be more than in each layer due
to combinations).
Attributes of both layers are appended.

If you get errors due to invalid geometries, well, then correct that
beforehand.

Martin
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Re: [QGIS-it-user] help algoritmo ricampionamento

2018-01-17 Thread rosa.coluzzi

Perfetto, grazie mille. Credo di aver avuto la risposta alla mia domanda e 
soprattutto grazie per aver specificato che il ricampionamento avviene "a 
monte" del processamento! 
:-) 


Da: "G. Allegri"  
A: "Stefano Campus"  
Cc: "rosa.coluzzi" , "qgis-it-user" 
 
Inviato: Mercoledì, 17 gennaio 2018 9:02:25 
Oggetto: Re: [QGIS-it-user] help algoritmo ricampionamento 

Ok, comunque a quanto vedo dal codice la cosa non viene gestita esplicitamente 
ma è delegata al provider dei dati. 

Giovanni 

Il 17 gen 2018 08:30, "Stefano Campus" < [ mailto:skam...@gmail.com | 
skam...@gmail.com ] > ha scritto: 



Il ricampionamento avviene non solo per le diverse dimensioni delle celle tra 
raster ma anche, come forse malamente cercavo si spiegare, se sono 'sfasati'. 
Da questo punto di vista SAGA permette di scegliere il tipo di ricampionamento. 

Il 17/Gen/2018 00:24, "G. Allegri" < [ mailto:gioha...@gmail.com | 
gioha...@gmail.com ] > ha scritto: 

BQ_BEGIN

Capito la domanda... non mi tornava perché, in realtà, QGIS non fa nessun 
ricampionamento nel calcolatore raster. Nel caso in cui colonne/righe (quindi 
risoluzione) dell'output fosse diverso dall'input, QGIS (in realtà il provider 
GDAL) legge i dati originali sotto/sovra campionati. Quindi il "campionamento" 
è a monte, non a valle. Da una rapida lettura del codice GDAL a cui QGIS delega 
la lettura del raster, dovrebbe essere usato un campionamento "nearest 
neighbour" [1]. 
giovanni 

[1] [ https://github.com/OSGeo/gdal/blob/trunk/gdal/gcore/rasterio.cpp#L971 | 
https://github.com/OSGeo/gdal/blob/trunk/gdal/gcore/rasterio.cpp#L971 ] 

Il giorno 16 gennaio 2018 22:03, G. Allegri < [ mailto:gioha...@gmail.com | 
gioha...@gmail.com ] > ha scritto: 

BQ_BEGIN

Scusate, giusto per capire, ma l'estensione riguarda eventualmente un ritaglio, 
perché dite che viene fatto un ricampionamento? 
Comunque darò un occhio al codice... 

giovanni 

Il 16 gen 2018 18:09, "rosa.coluzzi" < [ mailto:rosa.colu...@imaa.cnr.it | 
rosa.colu...@imaa.cnr.it ] > ha scritto: 

BQ_BEGIN


Si, esatto, mi riferisco al calcolatore raster che consente di fare anche 
ricampionamenti (anche se i file sono registrati). Questo viene fatto se gli si 
chiede di riportare il file da processare all' "estensione del layer in uso". 

Qualcuno sa per caso dirmi quale algoritmo applica (default)? 
Grazie 

Da: "Stefano Campus" < [ mailto:skam...@gmail.com | skam...@gmail.com ] > 
A: "G. Allegri" < [ mailto:gioha...@gmail.com | gioha...@gmail.com ] > 
Cc: "rosa.coluzzi" < [ mailto:rosa.colu...@imaa.cnr.it | 
rosa.colu...@imaa.cnr.it ] >, "qgis-it-user" < [ 
mailto:qgis-it-user@lists.osgeo.org | qgis-it-user@lists.osgeo.org ] > 
Inviato: Martedì, 16 gennaio 2018 15:48:17 
Oggetto: Re: [QGIS-it-user] help algoritmo ricampionamento 

Credo che se i raster non sono registrati, il raster risultante è ricampionato. 

s. 

Il 16/Gen/2018 02:53 PM, "G. Allegri" < [ mailto:gioha...@gmail.com | 
gioha...@gmail.com ] > ha scritto: 

BQ_BEGIN

Ciao Rosa, 
ti stai riferendo al calcolatore raster interno di QGIS? Quello sotto il menù 
Raster, per intenderci. 
In tal caso non ho capito la domanda, perché non mi pare che il calcolatore 
faccia ricampionamenti... 

Giovann 

Il giorno 16 gennaio 2018 10:55, rosa.coluzzi < [ 
mailto:rosa.colu...@imaa.cnr.it | rosa.colu...@imaa.cnr.it ] > ha scritto: 

BQ_BEGIN

Salve! 
Avrei bisogno di reperire una informazione in merito ad un algoritmo. Nello 
specifico ho bisogno di capire l'algoritmo utilizzato dal tool raster 
calculator quando ricampiona un raster alla risoluzione di quello corrente 
(ricampionamento geometrico). Di default quale algoritmo utilizza? 


grazie in anticipo 

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Re: [QGIS-it-user] help algoritmo ricampionamento

2018-01-17 Thread G. Allegri

Ok, comunque a quanto vedo dal codice la cosa non viene gestita
esplicitamente ma è delegata al provider dei dati.

Giovanni

Il 17 gen 2018 08:30, "Stefano Campus"  ha scritto:

> Il ricampionamento avviene non solo per le diverse dimensioni delle celle
> tra raster ma anche, come forse malamente cercavo si spiegare, se sono
> 'sfasati'. Da questo punto di vista SAGA permette di scegliere il tipo di
> ricampionamento.
>
> Il 17/Gen/2018 00:24, "G. Allegri"  ha scritto:
>
>> Capito la domanda... non mi tornava perché, in realtà, QGIS non fa nessun
>> ricampionamento nel calcolatore raster. Nel caso in cui colonne/righe
>> (quindi risoluzione) dell'output fosse diverso dall'input, QGIS (in realtà
>> il provider GDAL) legge i dati originali sotto/sovra campionati. Quindi il
>> "campionamento" è a monte, non a valle. Da una rapida lettura del codice
>> GDAL a cui QGIS delega la lettura del raster, dovrebbe essere usato un
>> campionamento "nearest neighbour" [1].
>>
>> giovanni
>>
>> [1] https://github.com/OSGeo/gdal/blob/trunk/gdal/gcore/rasterio.cpp#L971
>>
>> Il giorno 16 gennaio 2018 22:03, G. Allegri  ha
>> scritto:
>>
>>> Scusate, giusto per capire, ma l'estensione riguarda eventualmente un
>>> ritaglio, perché dite che viene fatto un ricampionamento?
>>> Comunque darò un occhio al codice...
>>>
>>> giovanni
>>>
>>> Il 16 gen 2018 18:09, "rosa.coluzzi"  ha
>>> scritto:
>>>

 Si, esatto, mi riferisco al calcolatore raster che consente di fare
 anche ricampionamenti (anche se i file sono registrati). Questo viene fatto
 se gli si chiede di riportare il file da processare all' "estensione del
 layer in uso".

 Qualcuno sa per caso dirmi quale algoritmo applica (default)?
 Grazie
 --
 *Da: *"Stefano Campus" 
 *A: *"G. Allegri" 
 *Cc: *"rosa.coluzzi" , "qgis-it-user" <
 qgis-it-user@lists.osgeo.org>
 *Inviato: *Martedì, 16 gennaio 2018 15:48:17
 *Oggetto: *Re: [QGIS-it-user] help algoritmo ricampionamento

 Credo che se i raster non sono registrati, il raster risultante è
 ricampionato.

 s.

 Il 16/Gen/2018 02:53 PM, "G. Allegri"  ha scritto:

> Ciao Rosa,
> ti stai riferendo al calcolatore raster interno di QGIS? Quello sotto
> il menù Raster, per intenderci.
> In tal caso non ho capito la domanda, perché non mi pare che il
> calcolatore faccia ricampionamenti...
>
> Giovann
>
> Il giorno 16 gennaio 2018 10:55, rosa.coluzzi <
> rosa.colu...@imaa.cnr.it> ha scritto:
>
>> Salve!
>> Avrei bisogno di reperire una informazione in merito ad un algoritmo.
>> Nello specifico ho bisogno di capire l'algoritmo utilizzato dal tool
>> raster calculator quando ricampiona un raster alla risoluzione
>> di quello corrente (ricampionamento geometrico). Di default quale
>> algoritmo utilizza?
>>
>>
>> grazie in anticipo
>>
>> ___
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>> QGIS-it-user@lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/qgis-it-user
>>
>>
>
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>


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