Re: [GRASS-user] Null values in attribute table get converted to 0 (zero) during v.to.rast

[Daniel Victoria]

I was traveling so could not respond. So sorry to chime in a bit late. For
me it was a bit counter intuitive that polygons with null attributes became
zero in the finished raster. What if I had attributes with zero value in it?

I liked the idea of issuing a warning and using the `where` parameter.

Anyway, thanks for the help and fix

Cheers
Daniel

On Fri, Nov 1, 2019 at 12:33 PM Micha Silver  wrote:

>
> On 01/11/2019 9:38, Markus Metz wrote:
>
>
>
> On Fri, Nov 1, 2019 at 12:11 AM Veronica Andreo 
> wrote:
> >
> > Hi Micha
> >
> > El jue., 31 oct. 2019 a las 22:36, Micha Silver ()
> escribió:
> >>
> >>
> >> On 31/10/2019 22:20, Markus Metz wrote:
> >>
> >>
> >>
> >> On Tue, Oct 29, 2019 at 7:40 PM Veronica Andreo 
> wrote:
> >> >
> >> > Hi Daniel,
> >> >
> >> > I agree that if there's a NULL in the column, there should be NULL in
> the resulting raster. I suggest to open a ticket here:
> https://trac.osgeo.org/grass/
> >>
> >> easy solution: v.to.rast where=" is not null"
> >>
> >> or the new PR #173
> >> https://github.com/OSGeo/grass/pull/173
> >> if an attribute value is null, the corresponding vector features will
> not be rasterized
> >>
> >> Markus M
> >>
> >> I'm not sure I agree with the approach that a polygon with missing
> attribute should become NULL. In my view, NULL should be used only for
> pixels not covered at all by any polygon.
> >
> > but in the resulting raster (in rasters in general), there's no
> difference, it's rather NULL or it has a value... it does not matter if the
> null comes from areas originally covered by a polygon or not...
>
> I think it depends on the particular use case if it matters where a NULL
> raster value comes from: a polygon with empty attribute or no polygon at
> all for that cell.
>
> >>
> >> Perhaps an additional input parameter "missing_attribute" so the user
> can choose a value to enter into the raster if the attribute is missing. If
> no parameter is supplied, and the chosen attribute column has missing
> values, I'd prefer that the script exit gracefully, with a message that a
> "missing_attribute" value is required.
>
> This can easily be done with existing tools:
> - convert only those polygons with a valid attribute value: v.to.rast
> where="attribute is not null"
> - replace missing attribute values with a valid value: v.db.update
> where="attribute is null", then v.to.rast
>
> I'm changing my PR to issue a warning if empty attribute values are found
> and replaced with zero.
>
>
> IMHO, that's probably the best way to deal with this.
>
>
>
> Markus M
>
> >
> > yes, this could be a solution to keep track of where you had polygons,
> but then you would need to use r.null anyway, no? I try to think of use
> cases in which one uses a vector attribute to convert to raster, but then
> still needs to know where the polygons were... because, for example, to
> query a raster map with another raster map representing zones one would
> convert the vector of polygons using cat and not an attribute, no?
> >
> > cheers,
> > Vero
> >>
> >>
> >> > El jue., 24 oct. 2019 a las 14:40, Daniel Victoria (<
> daniel.victo...@gmail.com>) escribió:
> >> >>
> >> >> Hi list,
> >> >>
> >> >> I have a vector polygon map that I'm converting to raster. The
> attribute column that I process has some empty rows (no data / null). When
> I run v.to.rast, these empty rows become 0 (zero) on my resulting raster
> map.
> >> >>
> >> >> Shouldn't v.to.rast respect the empty attribute table and create
> null values for those polygons?
> >> >>
> >> >> For now I'll use r.null to fix this problem. But what if 0 is a
> valid value?
> >> >>
> >> >> Cheers
> >> >> Daniel
> >> >>
> >> >> PS - Running Grass 7.6.1 on Ubuntu
> >> >> ___
> >> >> grass-user mailing list
> >> >> grass-user@lists.osgeo.org
> >> >> https://lists.osgeo.org/mailman/listinfo/grass-user
> >> >
> >> > ___
> >> > grass-user mailing list
> >> > grass-user@lists.osgeo.org
> >> > https://lists.osgeo.org/mailman/listinfo/grass-user
> >>
> >> ___
> >> grass-user mailing list
> >> grass-user@lists.osgeo.org
> >> https://lists.osgeo.org/mailman/listinfo/grass-user
> >>
> >> --
> >> Micha Silver
> >> Ben Gurion Univ.
> >> Sde Boker, Remote Sensing Lab
> >> cell: +972-523-665918
>
> --
> Micha Silver
> Ben Gurion Univ.
> Sde Boker, Remote Sensing Lab
> cell: +972-523-665918
>
> ___
> grass-user mailing list
> grass-user@lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
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Re: [GRASS-user] Null values in attribute table get converted to 0 (zero) during v.to.rast

[Micha Silver]

  
  

On 01/11/2019 9:38, Markus Metz wrote:


  
  

On Fri, Nov 1, 2019 at 12:11 AM Veronica Andreo 
wrote:
>
> Hi Micha
>
> El jue., 31 oct. 2019 a las 22:36, Micha Silver ()
escribió:
>>
>>
>> On 31/10/2019 22:20, Markus Metz wrote:
>>
>>
>>
>> On Tue, Oct 29, 2019 at 7:40 PM Veronica Andreo 
wrote:
>> >
>> > Hi Daniel,
>> >
>> > I agree that if there's a NULL in the column,
there should be NULL in the resulting raster. I suggest to open
a ticket here: https://trac.osgeo.org/grass/
>>
>> easy solution: v.to.rast
where=" is not null"
>>
>> or the new PR #173
>> https://github.com/OSGeo/grass/pull/173
>> if an attribute value is null, the corresponding vector
features will not be rasterized
>>
>> Markus M
>>
>> I'm not sure I agree with the approach that a polygon
with missing attribute should become NULL. In my view, NULL
should be used only for pixels not covered at all by any
polygon.
>
> but in the resulting raster (in rasters in general),
  there's no difference, it's rather NULL or it has a value...
  it does not matter if the null comes from areas originally
  covered by a polygon or not... 



I think it depends on the particular use case if it matters
  where a NULL raster value comes from: a polygon with empty
  attribute or no polygon at all for that cell.



>>
>> Perhaps an additional input parameter
"missing_attribute" so the user can choose a value to enter into
the raster if the attribute is missing. If no parameter is
supplied, and the chosen attribute column has missing values,
I'd prefer that the script exit gracefully, with a message that
a "missing_attribute" value is required.


This can easily be done with existing tools:
- convert only those polygons with a valid attribute value:
  v.to.rast where="attribute is not null"

- replace missing attribute values with a valid value:
  v.db.update where="attribute is null", then v.to.rast



I'm changing my PR to issue a warning if empty attribute
  values are found and replaced with zero.
  



IMHO, that's probably the best way to deal with this.



  


Markus M



>
> yes, this could be a solution to keep track of where you
had polygons, but then you would need to use r.null anyway, no?
I try to think of use cases in which one uses a vector attribute
to convert to raster, but then still needs to know where the
polygons were... because, for example, to query a raster map
with another raster map representing zones one would convert the
vector of polygons using cat and not an attribute, no?
>
> cheers,
> Vero
>>
>>
>> > El jue., 24 oct. 2019 a las 14:40, Daniel Victoria
()
escribió:
>> >>
>> >> Hi list,
>> >>
>> >> I have a vector polygon map that I'm
converting to raster. The attribute column that I process has
some empty rows (no data / null). When I run v.to.rast, these
empty rows become 0 (zero) on my resulting raster map.
>> >>
>> >> Shouldn't v.to.rast respect the empty
attribute table and create null values for those polygons?
>> >>
>> >> For now I'll use r.null to fix this problem.
But what if 0 is a valid value?
>> >>
>> >> Cheers
>> >> Daniel
>> >>
>> >> PS - Running Grass 7.6.1 on Ubuntu
>> >>
___
>> >> grass-user mailing list
>> >> grass-user@lists.osgeo.org
>> >> https://lists.osgeo.org/mailman/listinfo/grass-user
>> >
>> > ___
>> > grass-user mailing list
>> > grass-user@lists.osgeo.org
>> > https://lists.osgeo.org/mailman/listinfo/grass-user
>>
>> ___
>> grass-user mailing list
>> grass-user@lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/grass-user
>>
>> -- 
>> Micha Silver
>> Ben Gurion Univ.
>> Sde Boker, Remote Sensing Lab
>> cell: +972-523-665918

-- 
Micha Silver
Ben Gurion Univ.

Re: [GRASS-user] Null values in attribute table get converted to 0 (zero) during v.to.rast

[Markus Metz]

On Fri, Nov 1, 2019 at 12:11 AM Veronica Andreo 
wrote:
>
> Hi Micha
>
> El jue., 31 oct. 2019 a las 22:36, Micha Silver ()
escribió:
>>
>>
>> On 31/10/2019 22:20, Markus Metz wrote:
>>
>>
>>
>> On Tue, Oct 29, 2019 at 7:40 PM Veronica Andreo 
wrote:
>> >
>> > Hi Daniel,
>> >
>> > I agree that if there's a NULL in the column, there should be NULL in
the resulting raster. I suggest to open a ticket here:
https://trac.osgeo.org/grass/
>>
>> easy solution: v.to.rast where=" is not null"
>>
>> or the new PR #173
>> https://github.com/OSGeo/grass/pull/173
>> if an attribute value is null, the corresponding vector features will
not be rasterized
>>
>> Markus M
>>
>> I'm not sure I agree with the approach that a polygon with missing
attribute should become NULL. In my view, NULL should be used only for
pixels not covered at all by any polygon.
>
> but in the resulting raster (in rasters in general), there's no
difference, it's rather NULL or it has a value... it does not matter if the
null comes from areas originally covered by a polygon or not...

I think it depends on the particular use case if it matters where a NULL
raster value comes from: a polygon with empty attribute or no polygon at
all for that cell.

>>
>> Perhaps an additional input parameter "missing_attribute" so the user
can choose a value to enter into the raster if the attribute is missing. If
no parameter is supplied, and the chosen attribute column has missing
values, I'd prefer that the script exit gracefully, with a message that a
"missing_attribute" value is required.

This can easily be done with existing tools:
- convert only those polygons with a valid attribute value: v.to.rast
where="attribute is not null"
- replace missing attribute values with a valid value: v.db.update
where="attribute is null", then v.to.rast

I'm changing my PR to issue a warning if empty attribute values are found
and replaced with zero.

Markus M

>
> yes, this could be a solution to keep track of where you had polygons,
but then you would need to use r.null anyway, no? I try to think of use
cases in which one uses a vector attribute to convert to raster, but then
still needs to know where the polygons were... because, for example, to
query a raster map with another raster map representing zones one would
convert the vector of polygons using cat and not an attribute, no?
>
> cheers,
> Vero
>>
>>
>> > El jue., 24 oct. 2019 a las 14:40, Daniel Victoria (<
daniel.victo...@gmail.com>) escribió:
>> >>
>> >> Hi list,
>> >>
>> >> I have a vector polygon map that I'm converting to raster. The
attribute column that I process has some empty rows (no data / null). When
I run v.to.rast, these empty rows become 0 (zero) on my resulting raster
map.
>> >>
>> >> Shouldn't v.to.rast respect the empty attribute table and create null
values for those polygons?
>> >>
>> >> For now I'll use r.null to fix this problem. But what if 0 is a valid
value?
>> >>
>> >> Cheers
>> >> Daniel
>> >>
>> >> PS - Running Grass 7.6.1 on Ubuntu
>> >> ___
>> >> grass-user mailing list
>> >> grass-user@lists.osgeo.org
>> >> https://lists.osgeo.org/mailman/listinfo/grass-user
>> >
>> > ___
>> > grass-user mailing list
>> > grass-user@lists.osgeo.org
>> > https://lists.osgeo.org/mailman/listinfo/grass-user
>>
>> ___
>> grass-user mailing list
>> grass-user@lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/grass-user
>>
>> --
>> Micha Silver
>> Ben Gurion Univ.
>> Sde Boker, Remote Sensing Lab
>> cell: +972-523-665918
___
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Re: [GRASS-user] Null values in attribute table get converted to 0 (zero) during v.to.rast

[Veronica Andreo]

Hi Micha

El jue., 31 oct. 2019 a las 22:36, Micha Silver ()
escribió:

>
> On 31/10/2019 22:20, Markus Metz wrote:
>
>
>
> On Tue, Oct 29, 2019 at 7:40 PM Veronica Andreo 
> wrote:
> >
> > Hi Daniel,
> >
> > I agree that if there's a NULL in the column, there should be NULL in
> the resulting raster. I suggest to open a ticket here:
> https://trac.osgeo.org/grass/
>
> easy solution: v.to.rast where=" is not null"
>
> or the new PR #173
> https://github.com/OSGeo/grass/pull/173
> if an attribute value is null, the corresponding vector features will not
> be rasterized
>
> Markus M
>
> I'm not sure I agree with the approach that a polygon with missing
> attribute should become NULL. In my view, NULL should be used only for
> pixels not covered at all by any polygon.
>
but in the resulting raster (in rasters in general), there's no difference,
it's rather NULL or it has a value... it does not matter if the null comes
from areas originally covered by a polygon or not... A different story
might be if we go from raster to polygon...

> Perhaps an additional input parameter "missing_attribute" so the user can
> choose a value to enter into the raster if the attribute is missing. If no
> parameter is supplied, and the chosen attribute column has missing values,
> I'd prefer that the script exit gracefully, with a message that a
> "missing_attribute" value is required.
>
yes, this could be a solution to keep track of where you had polygons, but
then you would need to use r.null anyway, no? I try to think of use cases
in which one uses a vector attribute to convert to raster, but then still
needs to know where the polygons were... because, for example, to query a
raster map with another raster map representing zones one would convert the
vector of polygons using cat and not an attribute, no?

cheers,
Vero

>
> > El jue., 24 oct. 2019 a las 14:40, Daniel Victoria (<
> daniel.victo...@gmail.com>) escribió:
> >>
> >> Hi list,
> >>
> >> I have a vector polygon map that I'm converting to raster. The
> attribute column that I process has some empty rows (no data / null). When
> I run v.to.rast, these empty rows become 0 (zero) on my resulting raster
> map.
> >>
> >> Shouldn't v.to.rast respect the empty attribute table and create null
> values for those polygons?
> >>
> >> For now I'll use r.null to fix this problem. But what if 0 is a valid
> value?
> >>
> >> Cheers
> >> Daniel
> >>
> >> PS - Running Grass 7.6.1 on Ubuntu
> >> ___
> >> grass-user mailing list
> >> grass-user@lists.osgeo.org
> >> https://lists.osgeo.org/mailman/listinfo/grass-user
> >
> > ___
> > grass-user mailing list
> > grass-user@lists.osgeo.org
> > https://lists.osgeo.org/mailman/listinfo/grass-user
>
> ___
> grass-user mailing 
> listgrass-user@lists.osgeo.orghttps://lists.osgeo.org/mailman/listinfo/grass-user
>
> --
> Micha Silver
> Ben Gurion Univ.
> Sde Boker, Remote Sensing Lab
> cell: +972-523-665918
>
>
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Re: [GRASS-user] Null values in attribute table get converted to 0 (zero) during v.to.rast

[Micha Silver]

  
  

On 31/10/2019 22:20, Markus Metz wrote:


  
  

On Tue, Oct 29, 2019 at 7:40 PM Veronica Andreo 
wrote:
>
> Hi Daniel,
>
> I agree that if there's a NULL in the column, there should
be NULL in the resulting raster. I suggest to open a ticket
here: https://trac.osgeo.org/grass/


easy solution: v.to.rast where=" is
  not null"


or the new PR #173
https://github.com/OSGeo/grass/pull/173
if an attribute value is null, the corresponding vector
  features will not be rasterized


Markus M


  



I'm not sure I agree with the approach that a polygon with
  missing attribute should become NULL. In my view, NULL should be
  used only for pixels not covered at all by any polygon. 
Perhaps an additional input parameter "missing_attribute" so the
  user can choose a value to enter into the raster if the attribute
  is missing. If no parameter is supplied, and the chosen attribute
  column has missing values, I'd prefer that the script exit
  gracefully, with a message that a "missing_attribute" value is
  required.





  
>
> Cheers,
> Vero
>
> El jue., 24 oct. 2019 a las 14:40, Daniel Victoria ()
escribió:
>>
>> Hi list,
>>
>> I have a vector polygon map that I'm converting to
raster. The attribute column that I process has some empty rows
(no data / null). When I run v.to.rast, these empty rows become
0 (zero) on my resulting raster map.
>>
>> Shouldn't v.to.rast respect the empty attribute table
and create null values for those polygons?
>>
>> For now I'll use r.null to fix this problem. But what
if 0 is a valid value?
>>
>> Cheers
>> Daniel
>>
>> PS - Running Grass 7.6.1 on Ubuntu
>> ___
>> grass-user mailing list
>> grass-user@lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/grass-user
>
> ___
> grass-user mailing list
> grass-user@lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
  
  
  ___
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-- 
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918
  

___
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Re: [GRASS-user] Null values in attribute table get converted to 0 (zero) during v.to.rast

[Markus Metz]

On Tue, Oct 29, 2019 at 7:40 PM Veronica Andreo 
wrote:
>
> Hi Daniel,
>
> I agree that if there's a NULL in the column, there should be NULL in the
resulting raster. I suggest to open a ticket here:
https://trac.osgeo.org/grass/

easy solution: v.to.rast where=" is not null"

or the new PR #173
https://github.com/OSGeo/grass/pull/173
if an attribute value is null, the corresponding vector features will not
be rasterized

Markus M

>
> Cheers,
> Vero
>
> El jue., 24 oct. 2019 a las 14:40, Daniel Victoria (<
daniel.victo...@gmail.com>) escribió:
>>
>> Hi list,
>>
>> I have a vector polygon map that I'm converting to raster. The attribute
column that I process has some empty rows (no data / null). When I run
v.to.rast, these empty rows become 0 (zero) on my resulting raster map.
>>
>> Shouldn't v.to.rast respect the empty attribute table and create null
values for those polygons?
>>
>> For now I'll use r.null to fix this problem. But what if 0 is a valid
value?
>>
>> Cheers
>> Daniel
>>
>> PS - Running Grass 7.6.1 on Ubuntu
>> ___
>> grass-user mailing list
>> grass-user@lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/grass-user
>
> ___
> grass-user mailing list
> grass-user@lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
___
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Re: [GRASS-user] Null values in attribute table get converted to 0 (zero) during v.to.rast

[Markus Metz]

On Tue, Oct 29, 2019 at 7:40 PM Veronica Andreo 
wrote:
>
> Hi Daniel,
>
> I agree that if there's a NULL in the column, there should be NULL in the
resulting raster. I suggest to open a ticket here:
https://trac.osgeo.org/grass/

that would require to change db_select_CatValArray on library level here
https://github.com/OSGeo/grass/blob/master/lib/db/dbmi_client/select.c#L368
and here
https://github.com/OSGeo/grass/blob/master/lib/db/dbmi_client/select.c#L375

I can't estimate the side effects of any changes, this is a widely used
function, thus no easy fix. Please open a ticket.

Markus M

>
> Cheers,
> Vero
>
> El jue., 24 oct. 2019 a las 14:40, Daniel Victoria (<
daniel.victo...@gmail.com>) escribió:
>>
>> Hi list,
>>
>> I have a vector polygon map that I'm converting to raster. The attribute
column that I process has some empty rows (no data / null). When I run
v.to.rast, these empty rows become 0 (zero) on my resulting raster map.
>>
>> Shouldn't v.to.rast respect the empty attribute table and create null
values for those polygons?
>>
>> For now I'll use r.null to fix this problem. But what if 0 is a valid
value?
>>
>> Cheers
>> Daniel
>>
>> PS - Running Grass 7.6.1 on Ubuntu
>> ___
>> grass-user mailing list
>> grass-user@lists.osgeo.org
>> https://lists.osgeo.org/mailman/listinfo/grass-user
>
> ___
> grass-user mailing list
> grass-user@lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
___
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Re: [GRASS-user] Null values in attribute table get converted to 0 (zero) during v.to.rast

[Veronica Andreo]

Hi Daniel,

I agree that if there's a NULL in the column, there should be NULL in the
resulting raster. I suggest to open a ticket here:
https://trac.osgeo.org/grass/

Cheers,
Vero

El jue., 24 oct. 2019 a las 14:40, Daniel Victoria (<
daniel.victo...@gmail.com>) escribió:

> Hi list,
>
> I have a vector polygon map that I'm converting to raster. The attribute
> column that I process has some empty rows (no data / null). When I run
> v.to.rast, these empty rows become 0 (zero) on my resulting raster map.
>
> Shouldn't v.to.rast respect the empty attribute table and create null
> values for those polygons?
>
> For now I'll use r.null to fix this problem. But what if 0 is a valid
> value?
>
> Cheers
> Daniel
>
> PS - Running Grass 7.6.1 on Ubuntu
> ___
> grass-user mailing list
> grass-user@lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/grass-user
___
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[GRASS-user] Null values in attribute table get converted to 0 (zero) during v.to.rast

[Daniel Victoria]

Hi list,

I have a vector polygon map that I'm converting to raster. The attribute
column that I process has some empty rows (no data / null). When I run
v.to.rast, these empty rows become 0 (zero) on my resulting raster map.

Shouldn't v.to.rast respect the empty attribute table and create null
values for those polygons?

For now I'll use r.null to fix this problem. But what if 0 is a valid
value?

Cheers
Daniel

PS - Running Grass 7.6.1 on Ubuntu
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