tiling and 'cliping' DEMs

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tiling and 'cliping' DEMs

Rich Shepard
I am downloading and importing 1m LiDAR DEMs for a 667 mi^2 (1727.5 km^2)
drainage basin. These are all in 7.5' topographic quad sections. The files
take up a lot of disk space and memory when working with them.

I assume that by careful setting of the region I can display the individual
maps as a single map, and I can set a computational mask using the vector
basin watershed (boundary). Is there way to 'clip' the DEM using the
watershed map in the way that v.clip works with two vector maps? While the
workstation has 32G RAM and 2T of disk space I would like to limit the DEM
to the drainage basin itself and exclude all areas outside it.

Looking at all the r.* modules in core and extensions none strikes me as the
appropriate tool.

I'm open to advice on working with huge raster files.

Regards,

Rich
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Re: tiling and 'cliping' DEMs [UPDATE]

Rich Shepard
On Tue, 10 Sep 2019, Rich Shepard wrote:

> I am downloading and importing 1m LiDAR DEMs for a 667 mi^2 (1727.5 km^2)
> drainage basin. These are all in 7.5' topographic quad sections. The files
> take up a lot of disk space and memory when working with them.

Update: I found the 10m DEMs to replace the ones I lost when a disk failed.
The lower resolution DEMs are better suited to such a large drainage basin,
but the rest of my questions remail valid.

Rich
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Re: tiling and 'cliping' DEMs

Helmut Kudrnovsky
In reply to this post by Rich Shepard
Rich Shepard wrote

> I am downloading and importing 1m LiDAR DEMs for a 667 mi^2 (1727.5 km^2)
> drainage basin. These are all in 7.5' topographic quad sections. The files
> take up a lot of disk space and memory when working with them.
>
> I assume that by careful setting of the region I can display the
> individual
> maps as a single map, and I can set a computational mask using the vector
> basin watershed (boundary). Is there way to 'clip' the DEM using the
> watershed map in the way that v.clip works with two vector maps? While the
> workstation has 32G RAM and 2T of disk space I would like to limit the DEM
> to the drainage basin itself and exclude all areas outside it.
>
> Looking at all the r.* modules in core and extensions none strikes me as
> the
> appropriate tool.
>
> I'm open to advice on working with huge raster files.
>
> Regards,
>
> Rich
> _______________________________________________
> grass-user mailing list

> grass-user@.osgeo

> https://lists.osgeo.org/mailman/listinfo/grass-user

To save diskspace,, build a virtual raster with your tiles outside GRASS  by
GDAL's  buildvrt, do r.external yourvirtual.vrt.

No import is needed for raster calculations, r.external to link the virtual
raster works nicely..

regarding to clip a raster to  vector extent, there a several ways. One may
be: g.region  -a raster=yourraster vector=yourvector followed by a r.mask
vector=yourvector then r.mapcal clippedraster=yourraster



-----
best regards
Helmut
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best regards
Helmut
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Re: tiling and 'cliping' DEMs

NikosAlexandris
* Helmut Kudrnovsky <[hidden email]> [2019-09-10 20:12:09 -0700]:

>Rich Shepard wrote
>> I am downloading and importing 1m LiDAR DEMs for a 667 mi^2 (1727.5 km^2)
>> drainage basin. These are all in 7.5' topographic quad sections. The files
>> take up a lot of disk space and memory when working with them.
>>
>> I assume that by careful setting of the region I can display the
>> individual
>> maps as a single map, and I can set a computational mask using the vector
>> basin watershed (boundary). Is there way to 'clip' the DEM using the
>> watershed map in the way that v.clip works with two vector maps? While the
>> workstation has 32G RAM and 2T of disk space I would like to limit the DEM
>> to the drainage basin itself and exclude all areas outside it.
>>
>> Looking at all the r.* modules in core and extensions none strikes me as
>> the
>> appropriate tool.
>>
>> I'm open to advice on working with huge raster files.
>>
>> Regards,
>>
>> Rich
>> _______________________________________________
>> grass-user mailing list
>
>> grass-user@.osgeo
>
>> https://lists.osgeo.org/mailman/listinfo/grass-user
>
>To save diskspace,, build a virtual raster with your tiles outside GRASS  by
>GDAL's  buildvrt, do r.external yourvirtual.vrt.
>
>No import is needed for raster calculations, r.external to link the virtual
>raster works nicely..

If there is no need for a GDAL VRT, then, alternatively, link all tiles
as pseudo-raster maps in GRASS GIS' data base, of course using
`r.external`. Then, build a GRASS GIS virtual raster data set using
`r.buildvrt`. Clipping or "extracting" parts of this VRT will expectedly
work.

Nikos

>regarding to clip a raster to  vector extent, there a several ways. One may
>be: g.region  -a raster=yourraster vector=yourvector followed by a r.mask
>vector=yourvector then r.mapcal clippedraster=yourraster
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Re: tiling and 'cliping' DEMs

Rich Shepard
In reply to this post by Helmut Kudrnovsky
On Tue, 10 Sep 2019, Helmut Kudrnovsky wrote:

> To save diskspace,, build a virtual raster with your tiles outside GRASS
> by GDAL's buildvrt, do r.external yourvirtual.vrt.
>
> No import is needed for raster calculations, r.external to link the virtual
> raster works nicely..
>
> regarding to clip a raster to  vector extent, there a several ways. One may
> be: g.region  -a raster=yourraster vector=yourvector followed by a r.mask
> vector=yourvector then r.mapcal clippedraster=yourraster

Helmut,

This is exceptionally useful information. I've not looked closely at gdal
and don't know all its capabilities. Perhaps this could be added to the Wiki
as it's likely to be useful to others.

I greatly appreciate the lesson.

Best regards,

Rich
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Re: tiling and 'cliping' DEMs

Rich Shepard
In reply to this post by NikosAlexandris
On Wed, 11 Sep 2019, Nikos Alexandris wrote:

> If there is no need for a GDAL VRT, then, alternatively, link all tiles as
> pseudo-raster maps in GRASS GIS' data base, of course using `r.external`.
> Then, build a GRASS GIS virtual raster data set using `r.buildvrt`.
> Clipping or "extracting" parts of this VRT will expectedly work.

Nikos,

I've insufficient experience to know whether there is need for GDAL VRT. But
I'll look closely at what you and Helmut advise and gain some experience.

Many thanks,

Rich
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