For QGIS versions older than 3.22, you can create a conditional statement for what you want to do with this expression:
("DEM@1" < 0) * (-1) * "DEM@1" + ABS ( ("DEM@1" < 0) - 1) * "DEM@1"
100 -> 100
2 -> 2
-5 -> 5
-150 -> 150
Drape to transfer the raster values to your line vertices as z-values.
(I used Densify by interval first to add more vertices.)
Field Calculate mean z value of your vertices with:
(generate_series( 1, num_points( $geometry))), z(point_n($geometry, @element))))
The easiest way to turn negative to corresponding positive values in raster calculator without even using a conditional statement is simply the function abs():
ABS ( "DEM@1" )
See result for the area of the Jordan valley and the Dead Sea (red ouline) that is changed to positive values, whereas the rest remains: left - original DEM, right - output ...
In previous versions it simply performs an assignment, a conditional within a parenthesis followed by a *, performs an assignment to all pixels that meet that condition.
("DEM" < 0 ) *0 + ("DEM" >= 0 ) *"DEM"
It will convert all values less than 0 to 0, and leave all other pixels the same.
On the other hand, if ...
This worked for me:
Create a project folder somewhere. Mine is C:\GossanHill.
Put your .las files in there.
Get the LASTools
The programs we need don’t really need to be installed, just saved at a convenient location.
Get LASTools from rapidlasso.
Open the Lastools.zip file. Navigate to the bin folder. Copy these files to your project folder: las2las....
The accepted answer seems to be describing WHAT they are rather than HOW to choose them. (The only heuristics I'm seeing in the accepted answer: know how to use it, and don't when there are outliers)
It looks like you choose the interpolation method based on when:
A) You need to be certain of how accurate your resulting values are (like with hypothesis ...
If you simply want to create a barrier across the stream and don't care about side slopes of the dam:
Make a new shapefile and create a narrow polygon across the stream where you want the wall/dam.
Convert the polygon to raster (Polygon to Raster)
You may need to copy this new raster (Copy Raster) and set the "NoData Value" to zero to remove ...