Here we go then, a method to get some control over contour label placement, see the picture.
The first thing I did was to load the contours. Next, on a new line shapefile, I drew a line from the top of the hill to the bottom (the labels in the picture are aligned with this). I then buffered the line and used the buffer to clip the contour layer. After that ...
The simple trick to select only Integer values, is to use the following syntax:
Mod(Round("ELEVATION", 0)*10, 10)=0
This Multiplication by 10, makes all the values Integer, and then we select only those which are multiples of 10.
In case you wish to select Multiples of some other number, just multiply 10 by the interval.
To get contours at 5 m intervals, ...
Yes, doable. Normally I'd suggest a partially transparent buffer, but I see why you want to do this cartographically.
This could be slow, and you need to manually decide where you want the labels to go - but cartographically speaking, that's not a bad thing!
Here's a screenshot...
As you can see, no buffers. The raster underneath is unaffected. I've ...
In principle, you cannot do this in a unique, accurate way without reconstructing something like the original DEM.
Let's see why, by doing the computation with a (difficult but realistic) example. It begins with a small portion of a 30 meter DEM, about 15 by 11 kilometers.
Contours have been computed at regular intervals: this is where you begin.
Evaluation of the options
Contour lines represent continuous surfaces, so their comparison ultimately is a proxy for comparing those surfaces. Because both the surface values (elevations) and locations are potentially subject to error, there are two components to the comparison: in terms of value and in terms of position. The two cannot be separated, ...
In QGIS 2.6 (maybe earlier versions as well, I don't know) you can do this under the Layer Properties, Labels tab, Rendering section. About halfway down the list of rendering options is a button that will let you write an expression which will define the list of features that will actually be labeled. Your expression would be something like "Elevation" IN (...
I've experienced the same problems you area having in your second method. I exported a Raster to a Vector and try to and use v.generalise and I get mostly smooth polygons with the occasional 'stepped' boundary which appears to have been unaffected by the algorithm.
I found a process that worked for my task, not sure if its the best way but thought i'd share ...
To smooth your contours it is the best way to smooth your DEM first.
Here are some useful information: What raster smoothing/generalization tools are available?
I'm using SAGA GIS for this task.
Using SAGA GIS Version 6.2.0 directly: Grid > Filter > Gaussian Filter
Or use the QGIS Processing Toolbox and search for gaussian. Warning: Using QGIS 2.18....
One approach would be to load the contour layer and style it. Then load the same layer again and apply a filter (right-click on the layer and go down to 'Filter..') Use a filter expression similar to the one shown in the picture. In my case I wanted major contours at vertical intervals of 50 metres and the field containing the elevation values was called "...
If you are looking to convert DEMs to contour lines:
QGIS Plugin Contours
For converting scanned topo maps to vector contour lines, Arcscan is one of the easiest (and most sophisticated) programs out there. However, there are several opensource alternatives, including a promising GRASS approach:
Trace vector contours from a scanned map.
I would highly recommend going through the Contour lines to DEM tutorial, available from GRASS wiki. Essentially, they describe different interpolation methods used to produce a DEM. Avoid IDW interpolation using contour lines (i.e. described in one segment of the tutorial) since this is an inappropriate use of the interpolation method. The GRASS module ...
Try to do the following formula at Rule-based Style
"FieldName" % 1 = 0 (Assign thick lines for 1 meter interval lines)
ELSE (Assign thin lines or any other style for other interval lines)
In the above image "Elevation" is the name of the field that holds the contour elevation.
You can change the blend mode of the text buffer in label settings (see below).
Multiply works best if the buffer colour is a dark colour. However, that won't achieve what you have in your screenshot (see results below):
Instead, you should use the new Mask setting in QGIS 3.12 to mask out the line symbology in a buffer around the text.
First, in your ...
Here is another query option. It largely does the same as the answers listed above but is (in my opinion) a little bit easier to customise for different scenarios.
To display any contour divisible by 10
To display any contour divisible by 50
To display half metre contours
I assume your goal is to have different stroke weights for multiples of certain values - ie, one line weight for lines that are multiples of 10M, another for multiples of 100M, and so on. The details of how to do this depend on your software, but my general approach is to open the attribute table associated with the shapefile and add a new field which will ...
Sirgeo, don't try to fix up contours after they are generated, the processes take a long time and will eventually lead to intersecting contours = a nightmare!
Instead smooth your raster to take the lumps and bumps out - easier maths and no topology to worry about. I find resample slightly up (cellsize x 1.5) and then back down to the original (or better) ...
Slope analysis is performed on a DEM (raster layer with elevation values). This is one way to do it. If your contours have an elevation value, you can use the interpolation option (raster/interpolation) to produce a DEM. For instance, here are my contours as a shapefile
The attribute table do have a value for altitudes in the "elevacion" field.
Now you can ...
In the GRASS GIS Wiki, there is a dedicated page for this: http://grass.osgeo.org/wiki/Contour_lines_to_DEM The page demonstrates and compares a number of different methods of converting vector contour lines into raster DEM surfaces including screenshots.
In my case, I have a DEM with continue values, going from 100 to 103 meters. The spatial resolution is 0.25 x 0.25 degrees, defined in EPSG:4326. The DEM is styled with a discrete color ramp with three classes:
To smooth it, first I will make a raster algebra. Because I want a raster with only three values. I am using the following formula:
I use the "Buffer" option on the "Label setting" tab. (Using the labels button, not the old labels option on the layer properties dialog.) This does not wipe out the contour line, as I imagine you are wanting to do, but it does make the label legible.
You can specify levels using the GRASS module, r.contour.level. It's available in the processing toolbox. You can search for it when the dropdown at the bottom of the Processing Toolbox window is switched from "Simplified interface" to "Advanced interface".
The "List of contour levels" parameter takes a comma separated list of elevation levels.
Here is ...
If it is 3D DXF, follow the steps:
import the dxf in QGIS (DRAG & DROP or CTRL + V);
save as vectors (as the right mouse button);
add new field Z (integer);
Browser Panel to create a new database spatialite;
DBManager to import the shape in the newly created database;
run the update query;
step 3 - add new field Z
step 5 -DB Manager
@pigreco's answer should work.
But here a simpler solution without the spatialite process (step 1 to 2 are the same).
Load your .dxf and export (save as...) as shapefile (or spatialite / postgis).
On the new layer, use the Field Calculator (accessible from the main toolbar or from the attribute table).
Setup the new column (name and type, virtual or not ...
You can do something similar using gdal_calc.py, e.g.:
gdal_calc.py -A dtm.tif --calc='((A>=100)*(A<=200))*A+((A<100)*0)+((A>200)*0)' --outfile=dtm_reclass.tif --NoDataValue=-32767
This calc expression would:
Assign a value of 0 to all pixel values less than 100 ((A<100)*0)
Assign a value of 0 to all pixel values greater than 200 ((A>200)...
Just a couple of examples are:
QGIS main menu Raster | Extraction | Contour
Processing Toolobox SAGA | Vector <-> raster | Contour lines (or SAGA | Vector to raster | Contour lines)
(1) QGIS Contour
After setting your input file and output filename, turn the bottom window into "edit mode" by clicking on the pencil mark. Then add -fl 4.54 in the ...
I think the closest it can get with current QGIS abilities is to use halo (or background) effect with color sourced from table which will be based on the elevation value and color scheme same as used for underlying grid. Of course this would not take into account hillshade and everything else below the halo in the map. Random color example:
With some bit ...
I used this tutorial to create a Digital Terrain Model (DTM).
It uses as input contour shapefiles converted in raster contours that are later interpolated in DTM (looks like a continuous heat map)
It is not using QGIS but just GRASS, but it may be feasible with the Grass plugin from QGIS.