[GRASS-user] Elevation above a river

[Shane Carey]

No worries, I'm not seeing any differences in the original and the filtered
cells. I've tried mode and max methods

Thanks

Le gach dea ghui,
*Shane Carey*
*GIS and Data Solutions Consultant*

On Sat, Sep 22, 2018 at 2:39 PM, johannesradinger <
johannesradinger at gmail.com> wrote:

> Sorry I ment method=mode or median as stated by Markus N.
>
>
>
> Sent from my Samsung Galaxy smartphone.
>
> -------- Original message --------
> From: Shane Carey <careyshan at gmail.com>
> Date: 22/09/2018 15:05 (GMT+01:00)
> To: Johannes Radinger <johannesradinger at gmail.com>
> Cc: Markus Neteler <neteler at osgeo.org>, GRASS user list <
> grass-user at lists.osgeo.org>
> Subject: Re: [GRASS-user] Elevation above a river
>
> This works a treat - super stuff - thanks Johannes.
>
> Could you point me in the direction of an algorithim with Grass that can
> do the following:
>
> # Clean some of the spurious cells etc. (using some kind of neighbourhood
> filtering)
>
> Thanks very much
>
> Le gach dea ghui,
> *Shane Carey*
> *GIS and Data Solutions Consultant*
>
> On Sun, Sep 16, 2018 at 8:46 PM, Johannes Radinger <
> johannesradinger at gmail.com> wrote:
>
>> That is were the third step should follow, i.e. using r.mapcalc to
>> identify all the cells that are 1m higher than the grown river
>> (irrespective in which distance from the river these cells are located).
>> The rasterized area could then be translated into a vector format using
>> r.to.vect.
>>
>> Here a small example of how the working flow could be using the North
>> Caroline example dataset:
>> ##############
>> # Set region
>> g.region raster=elevation at PERMANENT
>>
>> # Extract elevation of the streams
>> r.mapcalc --o expression="streams_elevation = if(
>> streams_derived at PERMANENT, elevation at PERMANENT,null())"
>>
>> # Grow stream_elevation map by a some hundred meters
>> r.grow -m --overwrite input=streams_elevation
>> output=streams_elevation_grow radius=500
>>
>> # Calculate difference between original elevatoin and stream channel
>> elevation
>> r.mapcalc expression="stream_elevation_diff = elevation at PERMANENT -
>> streams_elevation_grow" --overwrite
>>
>> # Extract areas that are than x meters higher than stream channel
>> elevation
>> r.mapcalc expression="stream_elevation_diff_smaller1 = if(
>> stream_elevation_diff < 1,1,null())" --overwrite
>>
>> # Maybe here it needs some cleaning of spurious cells etc. (using some
>> kind of neighbourhood filtering)
>>
>> # Raster areas to a vector area (with smoothed corners; s-flag)
>> r.to.vect -s --overwrite input=stream_elevation_diff_smaller1
>> output=stream_elevation_diff_smaller1_area type=area
>> ##############
>>
>> HTH
>> /Johannes
>>
>> On Sun, Sep 16, 2018 at 8:53 PM Shane Carey <careyshan at gmail.com> wrote:
>>
>>> Hey Johannes,
>>>
>>> Thanks for your reply. How does r.grow work if let's say the height
>>> above the river reaches 1m at 3meters away from the river. And in an other
>>> area it reaches the 1meter height at 2meters away from the river. Is it
>>> able to follow that line?
>>>
>>> Thanks
>>>
>>> On Domh 16 MFómh 2018 at 17:21, Johannes Radinger <
>>> johannesradinger at gmail.com> wrote:
>>>
>>>> To me this looks like a flooding-related question, i.e. to extract the
>>>> shore lines of a river if it's water level is raised by 1m or 3m?
>>>> Maybe (1) extract the raster cells of the elevation map that represents
>>>> the river channel, (2) then apply r.grow and (3) then r.mapcalc to subtract
>>>> the grown river channel from the original elevation map.
>>>> /Johannes
>>>>
>>>> On Sun, Sep 16, 2018 at 5:16 PM Markus Neteler <neteler at osgeo.org>
>>>> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> Shane Carey <careyshan at gmail.com> schrieb am Fr., 14. Sep. 2018,
>>>>> 23:02:
>>>>>
>>>>>> Hi All,
>>>>>>
>>>>>> Does anyone know is it possible to calculate the elevation above a
>>>>>> river channel (actual river network that was digitised as opposed to being
>>>>>> extracted from a DTM) from a DTM and create a polygon from it.
>>>>>>
>>>>>> I need to calculate heights of 1m and 3m above a river channel on
>>>>>> both sides of the channel and create a polygon from it.
>>>>>>
>>>>>
>>>>> This isn't clear to me. Could you elaborate?
>>>>>
>>>>> Best
>>>>> Markus
>>>>>
>>>>>
>>>>> Thanks all.
>>>>>>
>>>>>> Le gach dea ghui,
>>>>>> *Shane Carey*
>>>>>> *GIS and Data Solutions Consultant*
>>>>>> _______________________________________________
>>>>>> grass-user mailing list
>>>>>> grass-user at lists.osgeo.org
>>>>>> https://lists.osgeo.org/mailman/listinfo/grass-user
>>>>>
>>>>> _______________________________________________
>>>>> grass-user mailing list
>>>>> grass-user at lists.osgeo.org
>>>>> https://lists.osgeo.org/mailman/listinfo/grass-user
>>>>
>>>> --
>>> Le gach dea ghui,
>>> *Shane Carey*
>>> *GIS and Data Solutions Consultant*
>>>
>>
>
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