[GRASS-user] r.grow.distance can't create meters instead of map units

Dimitris_sal · August 2, 2019, 6:58am

Hello everyone

My first post in this list,

So i am trying to create a raster with r.grow.distance. If i use the normal options everything works like the proximity analysis of QGIS, but when I try to add the advanced parameter Output distances in meters instead of map units i get the error “ERROR: Output distance in meters for lat/lon is only possible with ‘metric=geodesic’”

How do i add in the metrics the geodesic? I only have 4 euclidean,manhattan,squared,maximum.

Is there any alternative to create the raster in meters instead of map units?

Kind regards
Dimitris

neteler · August 2, 2019, 9:53am

Hi Dimitris,

On Fri, Aug 2, 2019 at 8:58 AM Dimitris sal <jimmaras123@gmail.com> wrote:

Hello everyone

My first post in this list,

So i am trying to create a raster with r.grow.distance.

As you are working via QGIS, in which projection do you work?

If i use the normal options everything works like the proximity analysis of QGIS, but when I try to add the advanced parameter Output distances in meters instead of map units i get the error "ERROR: Output distance in meters for lat/lon is only possible with 'metric=geodesic'"

How do i add in the metrics the geodesic? I only have 4 euclidean,manhattan,squared,maximum.

Yes, this is a limitation in QGIS processing (for whatever reason).
The parameters made available to the QGIS users are often a subset of
those provided by GRASS GIS.

# GRASS GIS
r.grow.distance --help
...
   metric Metric
             options: euclidean,squared,maximum,manhattan,geodesic
             default: euclidean

The change would be needed here:
https://github.com/qgis/QGIS/blob/release-3_8/python/plugins/processing/algs/grass7/description/r.grow.distance.txt

Is there any alternative to create the raster in meters instead of map units?

As a local workaround, you can simply search for r.grow.distance.txt
on your computer and add the missing "geodesic" there.
(and open an issue with the QGIS project or open a pull request with
the change there, or someone else does that).

Best,
Markus

--
Markus Neteler, PhD
https://www.mundialis.de - free data with free software
https://grass.osgeo.org
https://courses.neteler.org/blog

Dimitris_sal · August 2, 2019, 10:14am

Hello
In order to fix it I had to enable the GRASS plugin (is already installed) then import the raster , and run the plugin’s r.grow.distance with geodesic and it worked.

I just tried this and it worked Thanks for your help!!!

As a local workaround, you can simply search for r.grow.distance.txt
on your computer and add the missing “geodesic” there.
(and open an issue with the QGIS project or open a pull request with
the change there, or someone else does that).

Kind regards
Dimitris

Στις Παρ, 2 Αυγ 2019 στις 12:53 μ.μ., ο/η Markus Neteler <neteler@osgeo.org> έγραψε:

Hi Dimitris,

On Fri, Aug 2, 2019 at 8:58 AM Dimitris sal <jimmaras123@gmail.com> wrote:

Hello everyone

My first post in this list,

So i am trying to create a raster with r.grow.distance.

As you are working via QGIS, in which projection do you work?

If i use the normal options everything works like the proximity analysis of QGIS, but when I try to add the advanced parameter Output distances in meters instead of map units i get the error “ERROR: Output distance in meters for lat/lon is only possible with ‘metric=geodesic’”

How do i add in the metrics the geodesic? I only have 4 euclidean,manhattan,squared,maximum.

Yes, this is a limitation in QGIS processing (for whatever reason).
The parameters made available to the QGIS users are often a subset of
those provided by GRASS GIS.

QGIS processing

grep Metric /usr/share/qgis/python/plugins/processing/algs/grass7/description/r.grow.distance.txt
QgsProcessingParameterEnum|metric|Metric|euclidean;squared;maximum;manhattan|False|0|True

GRASS GIS

r.grow.distance --help
…
metric Metric
options: euclidean,squared,maximum,manhattan,geodesic
default: euclidean

The change would be needed here:
https://github.com/qgis/QGIS/blob/release-3_8/python/plugins/processing/algs/grass7/description/r.grow.distance.txt

Is there any alternative to create the raster in meters instead of map units?

As a local workaround, you can simply search for r.grow.distance.txt
on your computer and add the missing “geodesic” there.
(and open an issue with the QGIS project or open a pull request with
the change there, or someone else does that).

Best,
Markus

–
Markus Neteler, PhD
https://www.mundialis.de - free data with free software
https://grass.osgeo.org
https://courses.neteler.org/blog