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<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">Hi Stefan,</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">these weblinks were indeed very helpful to get me started. You can find anything on the internet, the trick is to know what exactly to look for and where to look. So thanks a lot for that!</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">With the help of that and further research I managed to create pretty much the map I needed. I will point out the steps later for others users.</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">There is just one problem left to be solved. The area of interest is quite small and has an irregularly shaped outline with a blank gap in the middle containing no data. Also some of the elevation isolines are offset by tectonic faults. I will try to attach a picture of one of the files to make that clear: top edge of the horizon, showing the outline (blue), elevation isolines (green) [m NHN], and tectonic faults (red). </span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">With the TIN Interpolation Tool (which appears to be the only one to work with lines as input features instead of points) the interpolation will just go across the gaps and the tectonic faults, giving wrong results.</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;"><span style="font-family: Wingdings;">à</span> So my question is: Is there a way to exclude areas from the TIN interpolation? Or mark boundaries where the interpolation will stop and create sharp edges rather than interpolating values on both sides of the tectonic fault or no-data-gap?</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">Ideally I would like to exclude polygons from the TIN interpolation. This would be applicable to the outline as well as the tectonic faults, as the faults could also be displayed as very long and narrow polygons instead of lines. If that would be easier?</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">In the TIN interpolation tool I tried setting the output extent to a polygon with the desired outline, but it seems to still cover the whole area assuming a rectangular extent.</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">Also I used the “clip raster by mask layer” tool, but this only works after the rasterization process, so I still get the wrong values from the interpolation.</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">I found this thread, but the answer is only for point features. <a href="https://gis.stackexchange.com/questions/116871/qgis-interpolate-along-an-irregular-shape-or-line-to-create-a-dem" target="_blank">https://gis.stackexchange.com/questions/116871/qgis-interpolate-along-an-irregular-shape-or-line-to-create-a-dem</a></span></span></span></p>
<p style="margin-bottom: 13.0px;"> </p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">Hi </span></span></span>Fernando M. Roxo da Motta<span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">,</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">Thanks for your answer. Maybe I wasn’t clear enough. The input data is not just two lines, it is two sets of line features. One set of elevation isolines for the top level of the horizon and one for the bottom level of the horizon, covering a small area of few square kilometres (i hope you can see the attached picture). This is all the data I have available. I already managed to get the vertical thickness of the layer, but I am still struggling with the interpolation going across tectonic faults and no data gaps as mentioned above. Do you have any experience in that matter?</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">Regards,</span></span></span></p>
<p style="margin-bottom: 13.0px;"><span style="font-size: 11.0pt;"><span style="line-height: 115.0%;"><span style="font-family: Calibri , sans-serif;">Eva</span></span></span></p>
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<div style="margin: 0 0 10.0px 0;"><b>Gesendet:</b> Mittwoch, 04. November 2020 um 14:08 Uhr<br/>
<b>Von:</b> "Fernando M. Roxo da Motta" <petro@roxo.org><br/>
<b>An:</b> qgis-user@lists.osgeo.org<br/>
<b>Betreff:</b> Re: [Qgis-user] How to get the thickness of a geol. layer from elevation isoline features</div>
<div>On Tue, 3 Nov 2020 14:39:02 +0100, fantypus@web.de wrote:<br/>
<br/>
<br/>
> Hi all,<br/>
<br/>
Hi Eva,<br/>
<br/>
I am an exploration geophysicist and what is bellow is based on my<br/>
prior experience.<br/>
<br/>
I suppose those two lines are based on interpretation of profiles of<br/>
some sort (seismic, EMT, eletromagnetic, grav, or whatever). My<br/>
question is:<br/>
<br/>
Are those lines just top and base of the layer of interest, or are<br/>
they crossing lines each one with the top and base of the layers?<br/>
<br/>
If those lines are in the same position containing just the top and<br/>
base of a geological layer it will be difficult, or just meaningless,<br/>
to extend those laterally to cover an area. If you have just a 2D<br/>
profile of the underground it has no information of the surrounding<br/>
area.<br/>
<br/>
If those are two crossing lines, each one with the top and base depth<br/>
(or time) of the layer of interest, you may rasterize (interpolate) them<br/>
to cover an area. The decision on how meaningful this interpolation<br/>
will be depends on many factors.<br/>
<br/>
The ideal scenario would be to have a grid survey to be rasterized,<br/>
this would produce a result with more meaning.<br/>
<br/>
HTH<br/>
<br/>
<br/>
><br/>
> I have the following task:<br/>
><br/>
> I need to create a map with contour lines showing the thickness of<br/>
> one geological layer/horizon (actually not the true thickness, but<br/>
> the vertical extent is required, so if you drill down at one point,<br/>
> what is the distance between the upper and lower edge of the horizon).<br/>
><br/>
> The only data I have are two line features (shape files) of isolines<br/>
> with elevation values (in m NHN) of each the upper edge and lower<br/>
> edge of the horizon.<br/>
><br/>
> My approach would be something like this, but I can’t figure out how<br/>
> exactly to do it:<br/>
> • Create a raster from each line feature (did that, but only the<br/>
> lines are rastered, so would need a polygon to get a plane? How do<br/>
> that? How can I include the elevation values of the lines into the<br/>
> polygon?)<br/>
> • Interpolate the elevation values inbetween the isolines to receive<br/>
> a plane of elevation values (in my opinion would need a polygon to<br/>
> get a plane, but for interpolation input Points are needed? And which<br/>
> interpolation method? Also, some of the isolines are offset by<br/>
> faults, so need sharp edges in these areas, how to integrate that in<br/>
> the interpolation?)<br/>
> • Then calculate the vertical distance at each point in the area<br/>
> between the two planes to get the thickness (how, which tool does<br/>
> that?)<br/>
> • Create a raster showing the thickness throughout the area in colour<br/>
> range<br/>
> • Add contour lines showing the thickness of the horizon<br/>
><br/>
> Maybe there is even a better and probably much simpler way to do<br/>
> this. However, I am only a beginner in QGIS, python and statistics.<br/>
> So any help and easy to understand tips will be very much<br/>
> appreciated. I am using QGIS 3.10.11 by the way.<br/>
><br/>
> Best regards,<br/>
><br/>
> Eva<br/>
><br/>
<br/>
<br/>
<br/>
<br/>
<br/>
<br/>
<br/>
<br/>
Roxo<br/>
<br/>
--<br/>
---------------- Non luctari, ludare -------------------+ WYSIWYG<br/>
Fernando M. Roxo da Motta <petro@roxo.org> | Editor?<br/>
Except where explicitly stated I speak on my own behalf.| VI !!<br/>
PU5RXO | I see text,<br/>
------------ Quis custodiet ipsos custodes?-------------+ I get text!<br/>
<br/>
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