Re: [Qgis-user] Working with DEMs

[Fernando M. Roxo da Motta]

 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.gardi...@gmail.com>
> > >>> Date: 2019-12-10 11:43 PM (GMT-05:00)
> > >>> To: qgis-user@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
> > >>> ___ Qgis-user
> > >>> mailing list Qgis-user@lists.osgeo.org
> > >>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> > >>> Unsubscribe:
> > >>> https://lists.osgeo.org/mailman/listinfo/qgis-user  
> > >> ___
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> >  








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Re: [Qgis-user] Working with DEMs

[Nicolas Cadieux]

Hi

On 2019-12-16 5:36 p.m., Falk Huettmann wrote:

Hi there,

thanks,
just to elaborate, for those who are interested:

(I would like to see the study that has compared those DEM products;
it matters a lot for climate models, for instance; happy to read the 
citations).
You will find many on web of science or google scholar.  My own research 
has been presented at the 39th Canadian Symposium on Remote Sensing, 
Saskatoon, SK and chapter will be published soon for my Ph.D.


Getting precise DEMs remains a massive struggle, regardless of what 
people, govs and products claim.
What is needed is a 'Quality Standard', as well as metadata (FGDC, 
ISO) for transparency.

It's as simple as that.
While in QGIS it's not our maintastk, it matters a lot and for
added value.  So the more we can push for it, the  better, and include 
such tools.


Why are DEMs from contour lines 'good' ?
Because they come from an era where people worked more precise and 
used analoge methods,

e.g. digitizing drums.
You know what they say B.S in = B.S out.  If the input data is very 
precise, then the output will be good. DEMs from contour lines are far 
from perfect but they are much better than expected if the input data is 
reliable.  Building a slope model from that will definitely expose the 
problems with the DEM, but the elevations can be very good.


For your own quality control, compute manually slope2 (=2nd 
derivative) from a DEM and see what you get.
If you see irregularities, lines and tiles something is rather odd, 
caused by the DEM production process.


Very best
   Falk Huettmann









On Mon, Dec 16, 2019 at 9:44 AM Nicolas Cadieux 
mailto:nicolas.cadi...@archeotec.ca>> 
wrote:


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 mailto:havard.tve...@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.gardi...@gmail.com
<mailto:2dave.gardi...@gmail.com>>
>>> Date: 2019-12-10 11:43 PM (GMT-05:00)
>>> To: qgis-user@lists.osgeo.org <mailto:qgis-user@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
>>> ___
>>> Qgis-user mailing list
>>> Qgis-user@lists.osgeo.org <mailto:Qgis-user@lists.osgeo.org>
>>> List

Re: [Qgis-user] Working with DEMs

[Håvard Tveite]

Hi Dave,

When "Use Z-coordinate for interpolation" is checked, it must be
assumed that the Z coordinate will be used *instead* of the
value in the "Elevation" attribute.

But it is strange that this should cause the Exception / error
you experience.

The TIN Interpolator seems to works fine here (QGIS 3.4.14 on
Ubuntu 18.04) when using an attribute for the elevation.
I have not tested with Z-values.

Håvard

On 13.12.19 08:50 Dave Gardiner wrote:
> I see them all and every one I use fails. Take the TIN Interpolation for
> example for which my input was:
>
> Vector Layer = Vertices (this is the layer with the extracted vector
> endpoint nodes on)
> Interpolation Attribute = Elevation
> Use Z point for Interpolation - ticked
> Input Layer = (Vector Layer = Vertices, Attribute=ZCOORD, type=POINT)
> Interpolation Method=Linear
> Extent=Canvas Extend
>
> This is my error.
>
> Traceback (most recent call last):
> File
> "C:/PROGRA~2/QGIS3~1.4/apps/qgis-ltr/./python/plugins\processing\algs\qgis\TinInterpolation.py",
> line 187, in processAlgorithm
> writer.writeFile(feedback)
> Exception: unknown
>
> Execution failed after 16.94 seconds
>
> Any thoughts please?
>
> Dave
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Re: [Qgis-user] Working with DEMs

[Falk Huettmann]

Hi there,

thanks,
just to elaborate, for those who are interested:

(I would like to see the study that has compared those DEM products;
it matters a lot for climate models, for instance; happy to read the
citations).

Getting precise DEMs remains a massive struggle, regardless of what people,
govs and products claim.
What is needed is a 'Quality Standard', as well as metadata (FGDC, ISO) for
transparency.
It's as simple as that.
While in QGIS it's not our maintastk, it matters a lot and for
added value.  So the more we can push for it, the  better, and include such
tools.

Why are DEMs from contour lines 'good' ?
Because they come from an era where people worked more precise and used
analoge methods,
e.g. digitizing drums.

For your own quality control, compute manually slope2 (=2nd derivative)
from a DEM and see what you get.
If you see irregularities, lines and tiles something is rather odd, caused
by the DEM production process.

Very best
   Falk Huettmann









On Mon, Dec 16, 2019 at 9:44 AM Nicolas Cadieux <
nicolas.cadi...@archeotec.ca> wrote:

> 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  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.gardi...@gmail.com>
> >>> Date: 2019-12-10 11:43 PM (GMT-05:00)
> >>> To: qgis-user@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
> >>> ___
> >>> Qgis-user mailing list
> >>> Qgis-user@lists.osgeo.org
> >>> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> >>> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
> >> ___
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> >> List info: https://lists.osgeo.org/mailman/listinfo/qgis-user
> >> Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user
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Re: [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  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.gardi...@gmail.com>
Date: 2019-12-10 11:43 PM (GMT-05:00)
To: qgis-user@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?



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Re: [Qgis-user] Working with DEMs

[Bernd Vogelgesang]

Hey Dave,

whats up?

Sent you a raster and steps to reproduce. No answer?

Am 13.12.19 um 17:22 schrieb qgis-u...@stripfamily.net:

On 12/13/2019 8:20 AM, Dave Gardiner wrote:
> Hi
>
> I just can't find a suitable one in New zealand
>
> Dave
The SRTM covers New Zealand. This website provides
a fairly friendly interface to download 30M SRTM DEM tiles.

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Re: [Qgis-user] Working with DEMs

[qgis-user]

  
  
On 12/13/2019 8:20 AM, Dave Gardiner
  wrote:

Hi
  
  
  I just can't find a suitable one in New zealand
  
  
  Dave

The SRTM covers New Zealand. This website provides a fairly
friendly interface to download 30M SRTM DEM tiles.
  

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Re: [Qgis-user] Working with DEMs

[Nicolas Cadieux]

Hi,
Try an input and output paths without spaces or accents. Is your z value a int 
or float rather than a string (text)?
Nicolas

> Le 13 déc. 2019 à 02:50, Dave Gardiner <2dave.gardi...@gmail.com> a écrit :
> 
> I see them all and every one I use fails. Take the TIN Interpolation for
> example for which my input was:
> 
> Vector Layer = Vertices (this is the layer with the extracted vector
> endpoint nodes on)
> Interpolation Attribute = Elevation
> Use Z point for Interpolation - ticked
> Input Layer = (Vector Layer = Vertices, Attribute=ZCOORD, type=POINT)
> Interpolation Method=Linear
> Extent=Canvas Extend
> 
> This is my error.
> 
> Traceback (most recent call last):
> File
> "C:/PROGRA~2/QGIS3~1.4/apps/qgis-ltr/./python/plugins\processing\algs\qgis\TinInterpolation.py",
> line 187, in processAlgorithm
> writer.writeFile(feedback)
> Exception: unknown
> 
> Execution failed after 16.94 seconds
> 
> Any thoughts please?
> 
> Dave
> 
> 
> 
> 
> --
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Re: [Qgis-user] Working with DEMs

[Bernd Vogelgesang]

mhm, not a single one works?  can you send me a sample of your points?

Am 13.12.19 um 08:50 schrieb Dave Gardiner:

I see them all and every one I use fails. Take the TIN Interpolation for
example for which my input was:

Vector Layer = Vertices (this is the layer with the extracted vector
endpoint nodes on)
Interpolation Attribute = Elevation
Use Z point for Interpolation - ticked
Input Layer = (Vector Layer = Vertices, Attribute=ZCOORD, type=POINT)
Interpolation Method=Linear
Extent=Canvas Extend

This is my error.

Traceback (most recent call last):
File
"C:/PROGRA~2/QGIS3~1.4/apps/qgis-ltr/./python/plugins\processing\algs\qgis\TinInterpolation.py",
line 187, in processAlgorithm
writer.writeFile(feedback)
Exception: unknown

Execution failed after 16.94 seconds

Any thoughts please?

Dave




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Re: [Qgis-user] Working with DEMs

[Dave Gardiner]

I see them all and every one I use fails. Take the TIN Interpolation for
example for which my input was:

Vector Layer = Vertices (this is the layer with the extracted vector
endpoint nodes on)
Interpolation Attribute = Elevation
Use Z point for Interpolation - ticked
Input Layer = (Vector Layer = Vertices, Attribute=ZCOORD, type=POINT)
Interpolation Method=Linear
Extent=Canvas Extend

This is my error.

Traceback (most recent call last):
File
"C:/PROGRA~2/QGIS3~1.4/apps/qgis-ltr/./python/plugins\processing\algs\qgis\TinInterpolation.py",
line 187, in processAlgorithm
writer.writeFile(feedback)
Exception: unknown

Execution failed after 16.94 seconds

Any thoughts please?

Dave




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Re: [Qgis-user] Working with DEMs

[Bernd Vogelgesang]

just type "interpolation" into the search field of the tool box, and all
the functions will jump right into your face.

Am 13.12.19 um 07:55 schrieb Dave Gardiner:

Hi Harvard

I have extracted the nodes from the contour lines with the elevation field
extracted. Could you please explain further how I generate a raster using a
tin or spline interpolation. Where are these commands (Version 3.4.13).

Kind Regards
Dave



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Re: [Qgis-user] Working with DEMs

[Dave Gardiner]

Hi Harvard

I have extracted the nodes from the contour lines with the elevation field
extracted. Could you please explain further how I generate a raster using a
tin or spline interpolation. Where are these commands (Version 3.4.13).

Kind Regards
Dave



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Re: [Qgis-user] Working with DEMs

[Falk Huettmann]

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  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.gardi...@gmail.com>
>> Date: 2019-12-10 11:43 PM (GMT-05:00)
>> To: qgis-user@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?
>>
>>
>>
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Re: [Qgis-user] Working with DEMs

[Håvard Tveite]

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.gardi...@gmail.com>
> Date: 2019-12-10 11:43 PM (GMT-05:00)
> To: qgis-user@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?
> 
> 
> 
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Re: [Qgis-user] Working with DEMs

[kirk]

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.The resulting raster should work with the plugin.Sent from my 
Samsung Galaxy smartphone.
 Original message From: Dave Gardiner 
<2dave.gardi...@gmail.com> Date: 2019-12-10  11:43 PM  (GMT-05:00) To: 
qgis-user@lists.osgeo.org Subject: [Qgis-user] Working with DEMs I am trying to 
create a geological cross section using the qProf plugin. Thisasks for the 
source of the DEM on which to base the elevations. My problemis my source for 
the elevation data is vector layer of contours importedfrom 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___Qgis-user
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Re: [Qgis-user] Working with DEMs

[Bernd Vogelgesang]

Go to
https://gis.stackexchange.com/
search for:
qgis DEM from contours

lots of older threads , but this one should help
https://gis.stackexchange.com/q/330474/8202

see also the comments to the question.

Cheers,
bernd


Am 11.12.19 um 05:43 schrieb Dave Gardiner:

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?



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[Qgis-user] Working with DEMs

[Dave Gardiner]

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?



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