Re: [GRASS-user] finding distance to raster features in a given direction

[Glynn Clements]

Nick Gauthier wrote:

> Given a binary land/sea raster, I’m trying to calculate the shortest
> distance from each land cell to the sea within a range of wind directions
> (e.g. 85-95 degrees from north). The calculation is basically
> r.grow.distance with an extra parameter for the range of directions (or a
> raster of the input bearings at each cell) with which to restrict the
> spreading function.
> 
> I’d appreciated any advice on how to to implement something like this in
> GRASS.

If it was a specific angle (rather than a range), you could just
rotate/shear the raster so that the desired direction was vertical,
then calculate the vertical distance by accumulating along columns.

If you wanted to enumerate cells within a given distance from the sea,
you could use convolution via FFT. But this won't give you the
distance itself (it would give you the number of sea cells within the
upwind sector, which might be a reasonable approximation in some
cases).

Other thank that, I think that something like r.grow.distance could
work. You'd first need to orient the data so that the central
direction was vertical. I believe that you'd need to either:

a) use a horizontal resolution significantly higher than the vertical
resolution, so that the the half-angle was one "cell" in each
direction, or

b) consider N rows above at each step, rather than a single row, so
that at least one row has multiple cells taken into account.

The central idea is that the nearest upwind sea cell to any given land
cell is also the nearest upwind sea cell for at least one of its
upwind neighbors (essentially, the "is upwind of" relationship is
transitive).

-- 
Glynn Clements 
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[GRASS-user] finding distance to raster features in a given direction

[Nick Gauthier]

Hi,

Given a binary land/sea raster, I’m trying to calculate the shortest
distance from each land cell to the sea within a range of wind directions
(e.g. 85-95 degrees from north). The calculation is basically
r.grow.distance with an extra parameter for the range of directions (or a
raster of the input bearings at each cell) with which to restrict the
spreading function.

I’d appreciated any advice on how to to implement something like this in
GRASS.

I have an implementation in R that draws a line from each cell along the
given bearing and finds the length of the segment that intersects with a
land polygon (vectorized from the land/sea raster). This is slow for larger
rasters and doesn't apply to a range of directions, so it looks like
something closer to r.grow.distance is the way to go.

Thanks for any suggestions,
Nick

*Nicolas E. Gauthier*
Graduate Research Assistant, Center for Social Dynamics and Complexity
School of Human Evolution and Social Change
Arizona State University
nicolas.gauth...@asu.edu
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Re: [GRASS-user] v.net tools with polygons

[Mark Wynter]

Hi Daniel, 

I've done something similar - I call it "off road routing", and uses a regular 
lattice of nodes and arcs. You can then constrain the off road "network" by 
closing arcs that cross major watercourses, fence lines or where the terrain or 
vegetation is non navigatable. For farms, I added paddock boundaries as rings, 
as well as gate nodes that constrain movement between paddocks. In essence you 
build a network topology that reflects the off-road aspect of your network.  
Relevant to mining as well as agriculture.


> 
> Ok Moritz,
> 
> Thanks for the tips. I'll try to go the centroids way
> 
> Cheers
> Daniel
> 
> On Tue, Mar 3, 2015 at 5:35 AM, Moritz Lennert > wrote:
> 
>>> On 02/03/15 21:39, Daniel Victoria wrote:
>>> 
>>> Hi list,
>>> 
>>> I'm beginning to learn and use the v.net  tools in Grass
>>> in order to evaluate the distance from several crop fields to a
>>> processing plant.
>>> 
>>> I've successfully build the road network with the end nodes but now I'm
>>> in doubt. My starting points in the analysis are crop fields, which are
>>> polygons. So what is the best (or most common) practice?
>>> 
>>> 1) Use the field centroids as starting nodes?
>>> 2) Add field polygon boundaries to the network and run v.net.distance
>>> backwards (from mill to fields)?
>>> 3) Some other option?
>> 
>> 
>> I don't think that there is a best practice for this. It all depends on
>> your application and the desired outcome. Do you want average time/distance
>> from anywhere in the field to the plant ? Then probably the centroid is ok.
>> Or do you want distance from the point of the field that is closest to the
>> network ? Then you could get the coordinates of that point through
>> v.distance (with upload=to_x,to_y) and use these points as nodes.
>> 
>> 
>> 
>> Also, if I'm to add the field boundaries to the network, how would I go
>>> about it? Should I first v.patch the field with the roads layer and then
>>> run v.net ?
>> 
>> Adding field boundaries still does not answer the question of where to put
>> the start/stop point of your paths...
>> 
>> If you want to add them to the network then yes, patching would be the
>> best option, AFAIK.
>> 
>> Moritz
>> 
>>  *
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Re: [GRASS-user] Syncronizing two displays

[Markus Neteler]

On Tue, Mar 3, 2015 at 1:18 PM, Daniel Victoria
 wrote:
> Is there a way to link two map displays in grass so that when I zoom into
> one display, the other follows? This would be very usefull for comparing
> raster and vector data, for instance.

For example, the g.gui.mapswipe does this.

Markus
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[GRASS-user] Syncronizing two displays

[Daniel Victoria]

Is there a way to link two map displays in grass so that when I zoom into
one display, the other follows? This would be very usefull for comparing
raster and vector data, for instance.

Cheers

Daniel
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Re: [GRASS-user] v.net tools with polygons

[Daniel Victoria]

Ok Moritz,

Thanks for the tips. I'll try to go the centroids way

Cheers
Daniel

On Tue, Mar 3, 2015 at 5:35 AM, Moritz Lennert  wrote:

> On 02/03/15 21:39, Daniel Victoria wrote:
>
>> Hi list,
>>
>> I'm beginning to learn and use the v.net  tools in Grass
>> in order to evaluate the distance from several crop fields to a
>> processing plant.
>>
>> I've successfully build the road network with the end nodes but now I'm
>> in doubt. My starting points in the analysis are crop fields, which are
>> polygons. So what is the best (or most common) practice?
>>
>> 1) Use the field centroids as starting nodes?
>> 2) Add field polygon boundaries to the network and run v.net.distance
>> backwards (from mill to fields)?
>> 3) Some other option?
>>
>
>
> I don't think that there is a best practice for this. It all depends on
> your application and the desired outcome. Do you want average time/distance
> from anywhere in the field to the plant ? Then probably the centroid is ok.
> Or do you want distance from the point of the field that is closest to the
> network ? Then you could get the coordinates of that point through
> v.distance (with upload=to_x,to_y) and use these points as nodes.
>
>
>
>  Also, if I'm to add the field boundaries to the network, how would I go
>> about it? Should I first v.patch the field with the roads layer and then
>> run v.net ?
>>
>
> Adding field boundaries still does not answer the question of where to put
> the start/stop point of your paths...
>
> If you want to add them to the network then yes, patching would be the
> best option, AFAIK.
>
> Moritz
>
>
>> Thanks
>> Daniel
>>
>>
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>>
>>
>
>
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[GRASS-user] Risultati XVI meeting utenti italiani GRASS GIS e GFOSS

[Elena Mezzini]

Ciao a tutti,

Ci scusiamo per l'eventuale cross-posting!

Con questo comunicato vorremmo ringraziare in primo luogo tutti gli
intervenuti al "XVI meeting degli utenti italiani di GRASS GIS e GFOSS"
tenutosi il 19 Febbraio scorso a Bologna.

La conferenza ha visto la presentazione di 10 interventi nei più svariati
campi, tra cui la presentazione della nuova realease di GRASS GIS, tenuta
direttamente da Markus Neteler, rilasciata ufficialmente il 22 febbraio 2015

Durante il code sprint ci siamo dedicati alla traduzione della
documentazione di GRASS GIS e di OSGeo Live, quest'ultimo rilasciato il 26
febbraio 2015

Circa 20 nuovi utenti hanno partecipato ai workshop introduttivi a QGIS e
GRASS GIS. Un sentito ringraziamento ai docenti.

Per chi fosse interessato, sul wiki dell'evento troverete il materiale
inerente i vari interventi.
http://grasswiki.osgeo.org/wiki/XVI_Meeting_degli_Utenti_Italiani_di_GRASS_GFOSS

Mentre, a breve, verranno pubblicate sul sito qui sotto alcune foto
dell'evento.
http://www.scienzeagrarie.unibo.it/it/eventi/convegno-xvi-meeting-degli-utenti-italiani-di-grass-e-gfoss

Arrivederci al prossimo anno!

X il comitato organizzatore

Elena
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Re: [GRASS-user] v.net tools with polygons

[Moritz Lennert]

On 02/03/15 21:39, Daniel Victoria wrote:

Hi list,

I'm beginning to learn and use the v.net  tools in Grass
in order to evaluate the distance from several crop fields to a
processing plant.

I've successfully build the road network with the end nodes but now I'm
in doubt. My starting points in the analysis are crop fields, which are
polygons. So what is the best (or most common) practice?

1) Use the field centroids as starting nodes?
2) Add field polygon boundaries to the network and run v.net.distance
backwards (from mill to fields)?
3) Some other option?



I don't think that there is a best practice for this. It all depends on 
your application and the desired outcome. Do you want average 
time/distance from anywhere in the field to the plant ? Then probably 
the centroid is ok. Or do you want distance from the point of the field 
that is closest to the network ? Then you could get the coordinates of 
that point through v.distance (with upload=to_x,to_y) and use these 
points as nodes.





Also, if I'm to add the field boundaries to the network, how would I go
about it? Should I first v.patch the field with the roads layer and then
run v.net ?


Adding field boundaries still does not answer the question of where to 
put the start/stop point of your paths...


If you want to add them to the network then yes, patching would be the 
best option, AFAIK.


Moritz



Thanks
Daniel


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