[Qgis-user] Working with DEMs

[Nicolas Cadieux]

Hi,

I agree Falk that DEMs made from contour lines have their problems 
(stepped slopes, flat areas, elevation drops in lakes...).  Depending on 
the input data, they can still be a very accurate model for elevation.  
I tested the SRTM, NASADEMs, Alos, ASTER and the CDED (Canadian Digital 
Elevation Data) in Canada with LiDAR in various environments.  
Surprisingly, The CDED, made from 50k contour line are still the most 
accurate elevation wise.

Nicolas Cadieux

On 2019-12-12 5:29 p.m., Falk Huettmann wrote:
> Hi there,
> my comment to that DEM/contour profile question is:
> if you have a contour map, it's usually a pretty poor DEM and representation
> of reality, e.g. nature has no lines...
> If you then create a raster (back again) from the contour, it gets circular
> and even worse = pretty odd. A double whammy.
>
> So I would never ever recommend doing this, in case the DEM or Contour data
> are to show any meaningful ground information, or are to be used for such.
>
> That's my view.
> Very best
>     Falk Huettmann
>
> On 12/12/19, Håvard Tveite <havard.tveite at nmbu.no> wrote:
>> On 11.12.2019 15:14, kirk wrote:
>>> Hi Bernd. You will have to create a raster dem from your contour data.
>>> First extract nodes from lines and ensure the elevation field is
>>> extracted.
>>> Once you have the point data, you can generate a raster using a tin or
>>> spline interpretation.
>> You can also create the raster DEM directly from the contour data
>> (for instance with the "TIN interpolation" algorithm, using your
>> contour layer as "Structured lines").
>>
>> Håvard
>>
>>> The resulting raster should work with the plugin.
>>>
>>>
>>>
>>> Sent from my Samsung Galaxy smartphone.
>>>
>>> -------- Original message --------
>>> From: Dave Gardiner <2dave.gardiner at gmail.com>
>>> Date: 2019-12-10 11:43 PM (GMT-05:00)
>>> To: qgis-user at lists.osgeo.org
>>> Subject: [Qgis-user] Working with DEMs
>>>
>>> I am trying to create a geological cross section using the qProf plugin.
>>> This
>>> asks for the source of the DEM on which to base the elevations. My problem
>>> is my source for the elevation data is vector layer of contours imported
>>> from a csv file. How do I create a DEM from this please?
>>>
>>>
>>>
>>> --
>>> Sent from: http://osgeo-org.1560.x6.nabble.com/QGIS-User-f4125267.html
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