Generating DEM from contour Shapefile using QGIS?

Question

I want to create a DEM from depth contours (shapefile) in QGIS. I've been trying to work out how to do this based on this previous question, notably from this link from that page, however I'm stuck, and was hoping someone could help.

My progress/process so far:

1. open new map in QGIS, import the contour shapefile
2. set GRASS extent, set new GRASS mapfile, etc
3. try to 'import' the shapefile into grass by converting it into a grass file, based on a hunch from the wording in this page (search in page: 'use of qgis and grass'): file management, import into grass, import vector into grass, import loaded vector (v.in.ogr.qgis), then view output. This creates an identical looking layer.
4. try to use r.surf.contour on this - doesn't allow layer to be selected.
5. try to use r.surf.contour2 on this - either crashes QGIS or produces a full block of colour.

Any thoughts/tips on what I should be doing differently?

---

Interpolation failing, tried everything in GRASS & in GRASS plugin, failed, could problem be due to source shapefile?

Something I learnt from elsewhere was 'geometry tools > check geometry validity' which I ran on the contour shapefile and it found loads of errors.

I'm wondering if this could be the reason that all my efforts to create a DEM are failing?

Would anyone do me the huge favour of having a look at my shapefile to see if I'm just being useless, or if it's a problem that a relative novice would be excused for not anticipating?

Answer 1

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.

Answer 2

I use the following procedure with great success. Open "Processing" toolbox inside QGIS, click on "SAGA", click on "Raster creation tools", and finally click on "Triangulation". In the "triangulation" dialog box, select the shape file that has the data points used to create the contour. Choose the attribute field that has the elevation data, specify the cell size. The smaller the value of the cell size the higher the resolution will be. Run and the raster file will be created and loaded as a memory layer.

Answer 3

The GRASS tutorial looks like the ticket. Following along your steps, are you converting the contours to raster somewhere between 1 and 4?

Last paragraph in the About section:

A number of the r.surf.* modules want the input data to be in raster form already, so we rasterize the contour lines, using the level column for the height values. Also some of the older r.surf.* modules only like to work on integers, so to preserve sub-meter fidelity we do a little trick where we multiply by a large number, do the process, then divide by that number again (to avoid terracing be sure it's floating point, not an integer).