[GRASS-user] r.mapcalculator and r.mapcalc

GRASS GRASS user
,
1

Hi there,
I have some questions regarding r.mapcalc questions:
1 - Why wasn’t r.mapcalculator ported to grass7? It is great to use it from within QGIS.
2 - My r.mapcalc outputs int32 rasters (I want float32). Is there a way to choose the output type?

Thanks!

Regards,
Luiz Claudio

2

1 - Why wasn’t r.mapcalculator ported to grass7? It is great to use it from

within QGIS.

can't answer this one

My r.mapcalc outputs int32 rasters (I want float32). Is there a way to

choose the output type?

from the manual [1]

------------------------
[...]
Functions
The functions currently supported are listed in the table below. The type of
the result is indicated in the last column. F means that the functions
always results in a floating point value, I means that the function gives an
integer result, and * indicates that the result is float if any of the
arguments to the function are floating point values and integer if all
arguments are integer.

[...]
Floating point values in the expression
Floating point values in the expression are handled in a special way. With
arithmetic and logical operators, if either operand is float, the other is
converted to float and the result of the operation is float. This means, in
particular that division of integers results in a (truncated) integer, while
division of floats results in an accurate floating point value. With
functions of type * (see table above), the result is float if any argument
is float, integer otherwise.

Note: If you calculate with integer numbers, the resulting map will be
integer. If you want to get a float result, add the decimal point to integer
number(s).

If you want floating point division, at least one of the arguments has to be
a floating point value. Multiplying one of them by 1.0 will produce a
floating-point result, as will using float():

      r.mapcalc "ndvi = float(lsat.4 - lsat.3) / (lsat.4 + lsat.3)"
[...]
------------------------

HTH

[1] https://grass.osgeo.org/grass73/manuals/r.mapcalc.html

-----
best regards
Helmut
--
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3

On Mon, Feb 20, 2017 at 4:22 PM, Luiz Andrade <lcoandrade@gmail.com> wrote:

1 - Why wasn’t r.mapcalculator ported to grass7? It is great to use it
from within QGIS.

Nobody really asked for that as far as I know. The porting should be quite
simple if you are interested in that. But that was not the issue. See
discussion here:

http://trac.osgeo.org/grass/ticket/2409#comment:187
http://trac.osgeo.org/grass/ticket/2409#comment:190

QGIS seemed to focus more on providing good native QGIS calc:

https://lists.osgeo.org/pipermail/qgis-developer/2016-October/045569.html
https://lists.osgeo.org/pipermail/qgis-developer/2016-October/045596.html

Of course, these things can be reevaluated anytime. Ideally in a ticket.

If you learn or ask more about it somewhere else, please write it back. I
would like to have the whole picture.

Vaclav

4

Thank you very much!
That was very helpful!

Atenciosamente,
Luiz Claudio

···

On Mon, Feb 20, 2017 at 4:22 PM, Luiz Andrade <lcoandrade@gmail.com> wrote:

1 - Why wasn’t r.mapcalculator ported to grass7? It is great to use it from within QGIS.

Nobody really asked for that as far as I know. The porting should be quite simple if you are interested in that. But that was not the issue. See discussion here:

http://trac.osgeo.org/grass/ticket/2409#comment:187

http://trac.osgeo.org/grass/ticket/2409#comment:190

QGIS seemed to focus more on providing good native QGIS calc:

https://lists.osgeo.org/pipermail/qgis-developer/2016-October/045569.html
https://lists.osgeo.org/pipermail/qgis-developer/2016-October/045596.html

Of course, these things can be reevaluated anytime. Ideally in a ticket.

If you learn or ask more about it somewhere else, please write it back. I would like to have the whole picture.

Vaclav

5

Thanks!
Can you help me with another thing?
My images have 15m pixels, after processing in r.mapcalc and exporting they have 62m pixels. How can I solve this?

Thanks again

Regards,
Luiz Claudio

Em 20 de fev de 2017, à(s) 18:42, Helmut Kudrnovsky <hellik@web.de> escreveu:

1 - Why wasn’t r.mapcalculator ported to grass7? It is great to use it from

within QGIS.

can’t answer this one

My r.mapcalc outputs int32 rasters (I want float32). Is there a way to

choose the output type?

from the manual [1]

[…]
Functions
The functions currently supported are listed in the table below. The type of
the result is indicated in the last column. F means that the functions
always results in a floating point value, I means that the function gives an
integer result, and * indicates that the result is float if any of the
arguments to the function are floating point values and integer if all
arguments are integer.

[…]
Floating point values in the expression
Floating point values in the expression are handled in a special way. With
arithmetic and logical operators, if either operand is float, the other is
converted to float and the result of the operation is float. This means, in
particular that division of integers results in a (truncated) integer, while
division of floats results in an accurate floating point value. With
functions of type * (see table above), the result is float if any argument
is float, integer otherwise.

Note: If you calculate with integer numbers, the resulting map will be
integer. If you want to get a float result, add the decimal point to integer
number(s).

If you want floating point division, at least one of the arguments has to be
a floating point value. Multiplying one of them by 1.0 will produce a
floating-point result, as will using float():

r.mapcalc “ndvi = float(lsat.4 - lsat.3) / (lsat.4 + lsat.3)”
[…]

HTH

[1] https://grass.osgeo.org/grass73/manuals/r.mapcalc.html

best regards
Helmut

View this message in context: http://osgeo-org.1560.x6.nabble.com/r-mapcalculator-and-r-mapcalc-tp5308738p5308742.html
Sent from the Grass - Users mailing list archive at Nabble.com.

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6

Hi Vaclav,

The problem with r.mapcalc in QGIS was this one:

https://hub.qgis.org/issues/6894

It was partially solved, but not completely. So, Victor had created a new raster calculator using native QGIS classes:

https://github.com/qgis/QGIS/pull/3779

Best regards,

Pedro

···

2017-02-21 0:11 GMT+00:00 Vaclav Petras <wenzeslaus@gmail.com>:

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grass-user@lists.osgeo.org
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On Mon, Feb 20, 2017 at 4:22 PM, Luiz Andrade <lcoandrade@gmail.com> wrote:

1 - Why wasn’t r.mapcalculator ported to grass7? It is great to use it from within QGIS.

Nobody really asked for that as far as I know. The porting should be quite simple if you are interested in that. But that was not the issue. See discussion here:

http://trac.osgeo.org/grass/ticket/2409#comment:187

http://trac.osgeo.org/grass/ticket/2409#comment:190

QGIS seemed to focus more on providing good native QGIS calc:

https://lists.osgeo.org/pipermail/qgis-developer/2016-October/045569.html
https://lists.osgeo.org/pipermail/qgis-developer/2016-October/045596.html

Of course, these things can be reevaluated anytime. Ideally in a ticket.

If you learn or ask more about it somewhere else, please write it back. I would like to have the whole picture.

Vaclav

7

Hi Pedro,

···

On Mon, Feb 20, 2017 at 7:36 PM, Pedro Venâncio <pedrongvenancio@gmail.com> wrote:

Hi Vaclav,

The problem with r.mapcalc in QGIS was this one:

https://hub.qgis.org/issues/6894

I forgot about this ticket. If I interpret the comments correctly there are still people who want r.mapcalculator despite its issues.

I also forgot about -l flag to list inputs and outputs in G7.2:

r.mapcalc “a = elevation + lakes” -l
output=a
input=elevation@PERMANENT,lakes@PERMANENT

It does not do the computation, it only lists the inputs and outputs. The was point to make writing the wrappers easier and more robust. See details here:

https://grass.osgeo.org/grass72/manuals/r.mapcalc.html
https://trac.osgeo.org/grass/ticket/2592
https://trac.osgeo.org/grass/changeset/67000

It was partially solved, but not completely. So, Victor had created a new raster calculator using native QGIS classes:

https://github.com/qgis/QGIS/pull/3779

Thanks for the info.

2017-02-21 0:11 GMT+00:00 Vaclav Petras <wenzeslaus@gmail.com>:

grass-user mailing list
grass-user@lists.osgeo.org
https://lists.osgeo.org/mailman/listinfo/grass-user

On Mon, Feb 20, 2017 at 4:22 PM, Luiz Andrade <lcoandrade@gmail.com> wrote:

1 - Why wasn’t r.mapcalculator ported to grass7? It is great to use it from within QGIS.

Nobody really asked for that as far as I know. The porting should be quite simple if you are interested in that. But that was not the issue. See discussion here:

http://trac.osgeo.org/grass/ticket/2409#comment:187

http://trac.osgeo.org/grass/ticket/2409#comment:190

QGIS seemed to focus more on providing good native QGIS calc:

https://lists.osgeo.org/pipermail/qgis-developer/2016-October/045569.html
https://lists.osgeo.org/pipermail/qgis-developer/2016-October/045596.html

Of course, these things can be reevaluated anytime. Ideally in a ticket.

If you learn or ask more about it somewhere else, please write it back. I would like to have the whole picture.

Vaclav

8

On Feb 21, 2017 1:34 AM, “Luiz Andrade” <lcoandrade@gmail.com> wrote:

Thanks!
Can you help me with another thing?
My images have 15m pixels, after processing in r.mapcalc and exporting they have 62m pixels. How can I solve this?

You will need to set the

https://grasswiki.osgeo.org/wiki/Computational_region

correctly.

Markus

9

Thank you very much!

In terms of best practices, if I work with several images with different resolutions, should I always set the region resolution before executing some raster calculation?

Or is it better to have different locations according to my images resolutions?

Thanks again!

Regards!

···

2017-02-21 3:44 GMT-03:00 Markus Neteler <neteler@osgeo.org>:

On Feb 21, 2017 1:34 AM, “Luiz Andrade” <lcoandrade@gmail.com> wrote:

Thanks!
Can you help me with another thing?
My images have 15m pixels, after processing in r.mapcalc and exporting they have 62m pixels. How can I solve this?

You will need to set the

https://grasswiki.osgeo.org/wiki/Computational_region

correctly.

Markus