Changing project resolution in qgis?

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Changing project resolution in qgis?

Kurt Springs
Hi,

I was wondering if it were possible to change a projects resolution in  
qgis.  I my project area consists of twenty one raster maps plus  
vector maps for the water (coast, lake, river).  I am adding in point  
vectors for archaeological sites. I get so far, and can go no further,  
because I the map is too big.  Each raster map is of a 20km by 20km  
region, at a 10m resolution.  I am thinking that the resolution  
doesn't need to be this high so I wanted to change it to a courser  
resolution.  I checked through the menu and didn't see anything that  
would obviously do this.

Can anyone help?

Kurt Springs
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Re: Changing project resolution in qgis?

Carson Farmer
Hi Kurt,
> I was wondering if it were possible to change a projects resolution in
> qgis.
Your project doesn't have a resolution itself...
> I my project area consists of twenty one raster maps plus vector maps
> for the water (coast, lake, river).  I am adding in point vectors for
> archaeological sites. I get so far, and can go no further, because I
> the map is too big.
What do you mean by this? Too big in terms of file size, or dimensions?
Too big to export?
> Each raster map is of a 20km by 20km region, at a 10m resolution.  I
> am thinking that the resolution doesn't need to be this high so I
> wanted to change it to a courser resolution.  I checked through the
> menu and didn't see anything that would obviously do this.
You'll probably need to re-sample the individual raster layers in GRASS.
If they aren't GRASS rasters layers already, you'll need to import the
layers into GRASS, and do your operations from there. Check the QGIS
documentation for instructions on importing layers into GRASS etc.

Hope that helps,

Carson
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Re: Changing project resolution in qgis?

pcav
Carson Farmer ha scritto:
> You'll probably need to re-sample the individual raster layers in GRASS.
> If they aren't GRASS rasters layers already, you'll need to import the
> layers into GRASS, and do your operations from there. Check the QGIS
> documentation for instructions on importing layers into GRASS etc.

This could also be done by gdal. As previously noted, wrapping gdal
commands into qgis would be very useful.
All the best.
pc
--
Paolo Cavallini, see: * http://www.faunalia.it/pc *
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Re: Changing project resolution in qgis?

alobo
In reply to this post by Kurt Springs
[hidden email] wrote:

> Message: 8 Date: Mon, 05 Jan 2009 17:27:10 +0100 From: Paolo Cavallini <[hidden email]> Subject: Re: [Qgis-user] Changing project resolution in qgis? To: Carson Farmer <[hidden email]> Cc: [hidden email], Kurt Springs <[hidden email]> Message-ID: <[hidden email]> Content-Type: text/plain; charset=ISO-8859-1 Carson Farmer ha scritto:
>> > You'll probably need to re-sample the individual raster layers in GRASS.
>> > If they aren't GRASS rasters layers already, you'll need to import the
>> > layers into GRASS, and do your operations from there. Check the QGIS
>> > documentation for instructions on importing layers into GRASS etc.
>
> This could also be done by gdal. As previously noted, wrapping gdal
> commands into qgis would be very useful.
> All the best.
> pc
> -- Paolo Cavallini, see: * http://www.faunalia.it/pc *

Actually, this capability should be within a set of "Raster Tools"
in qgis itself,
equivalent to the fTools contributed by Carson Farmer for vector layers.
Importing to GRASS for simple operations is inconvenient. Grass is meant
for cases in which many processing steps are going to be involved.
This is the same logic than the one for fTools for vector layers: in my
opinion, qgis must aim to provide basic operational capabilities for
both vector and raster layers.
There is a section "RasterSupportWishes" in the wiki, perhaps
it's time to start it?

Agus

--
Dr. Agustin Lobo
Institut de Ciencies de la Terra "Jaume Almera" (CSIC)
LLuis Sole Sabaris s/n
08028 Barcelona
Spain
Tel. 34 934095410
Fax. 34 934110012
email: [hidden email]
http://www.ija.csic.es/gt/obster
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Re: Re: Changing project resolution in qgis?

Borys Jurgiel
> > This could also be done by gdal. As previously noted, wrapping gdal
> > commands into qgis would be very useful.

and

> This is the same logic than the one for fTools for vector layers: in my
> opinion, qgis must aim to provide basic operational capabilities for
> both vector and raster layers.
> There is a section "RasterSupportWishes" in the wiki, perhaps
> it's time to start it?

A PyQGIS frontend for gdal is on my TODO list for a few months. I still
haven't time to learn the gdal api, but maybe calling the gdal binaries as
Paolo said would be the most optimal (gain/cost) way.
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Re: Re: Changing project resolution in qgis?

Borys Jurgiel
Monday 05 January 2009 23:33:10 I wrote:

> A PyQGIS frontend for gdal is on my TODO list for a few months. I still
> haven't time to learn the gdal api, but maybe calling the gdal binaries as
> Paolo said would be the most optimal (gain/cost) way.

Of course I mean only a short-term solution.
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Re: Changing project resolution in qgis?

alobo
In reply to this post by Kurt Springs
I agree with the short-term solution, which is
probably solving the problem that motivated the question.
But wanted to take the opportunity to propose
the idea of a set of Raster Tools, not relying
on grass for some common raster operations.
In this way the list is following the principle "Act short-term, think
long-term" :)

Agus

[hidden email] wrote:
------------------------------

Message: 4
Date: Mon, 5 Jan 2009 23:36:43 +0100
From: Borys Jurgiel <[hidden email]>
Subject: Re: [Qgis-user] Re: Changing project resolution in qgis?
To: [hidden email]
Message-ID: <[hidden email]>
Content-Type: text/plain;  charset="iso-8859-1"

Monday 05 January 2009 23:33:10 I wrote:

 > > A PyQGIS frontend for gdal is on my TODO list for a few months. I
still
 > > haven't time to learn the gdal api, but maybe calling the gdal
binaries as
 > > Paolo said would be the most optimal (gain/cost) way.

Of course I mean only a short-term solution.



--
Dr. Agustin Lobo
Institut de Ciencies de la Terra "Jaume Almera" (CSIC)
LLuis Sole Sabaris s/n
08028 Barcelona
Spain
Tel. 34 934095410
Fax. 34 934110012
email: [hidden email]
http://www.ija.csic.es/gt/obster
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Re: Re: Changing project resolution in qgis?

pcav
Agustin Lobo ha scritto:
> I agree with the short-term solution, which is
> probably solving the problem that motivated the question.
> But wanted to take the opportunity to propose
> the idea of a set of Raster Tools, not relying
> on grass for some common raster operations.
> In this way the list is following the principle "Act short-term, think
> long-term" :)

Agreed: GRASS should be used only for more complex operations, not for
simple tasks. However, I do not this reimplementing basic operations in
qgis would make much sense. The speedy development of fTools and other
python plugins is made possible by the reuse of existing libraries
(especially GEOS, etc.), and IMHO the same approach should be used for
rasters: a python plugin calling GDAL (same for OGR) will allow users to
greatly increase their power, without too much effort from qgis devs.
If important raster functions are missing from GDAL, better implement
them there than rewriting them in QGIS.
All the best.
pc
--
Paolo Cavallini, see: * http://www.faunalia.it/pc *
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