For the analyses of the excavation at HLO1 I created a digital terrain model of the site. A problem I encountered was caused by the wadi edge west of the site (see picture).
![Wadi Edge at HLO1 (seen from nort)](https://www.archaeomatics.de/wp-content/uploads/2013/02/wadi_edge-300x199.jpg)
For the surface interpolation I have measured hundreds of points all over the site and down towards the wadi. I have also measured the edge of the wadi terrace. As software I used GRASS-GIS (Version 6.4). Using all the points in one step yielded a Digital Terrain Model (DTM), where the edge of the Wadi is smoothed. Therefore I decided to do the interpolation in two steps.
![Measured points and faultline in red](https://www.archaeomatics.de/wp-content/uploads/2013/02/fault_lines1.png)
In the next step I used QGIS do digitest a close vector polygon (blue in the next picture) which includes all the points west of the faultline. This polygon I imported back in GRASS. You can also do this step directly in GRASS.
In the next step I wanted to use this polygon to create an vector mask. Before I could do this I had to run v.category on the vector layer with the polygon.
Now I could run v.to.rast to get a raster out of the close polygon. I used this raster as a mask with the command r.mask. Because of the mask the calculation in the next step is limited to the mask.
Last but not least I could calculate the surface west of the fault line. I used for example v.surf.rest to create an DTM from the west part.
![West part](https://www.archaeomatics.de/wp-content/uploads/2013/02/fault_lines5.png)
In the next step I had to use again the r.mask command but now with the -i flag to get an inverse Mask; Then we get a mask from the rest of the map and can calculate the DTM again.
![East part](https://www.archaeomatics.de/wp-content/uploads/2013/02/fault_lines4.png)
To combine the two raster files we have just created, we can use r.patch to get one big raster file from the whole site.
And here is the result:
![Final result](https://www.archaeomatics.de/wp-content/uploads/2013/02/fault_lines3.png)