# Talk:Using GRASS GIS through Python and tangible interfaces (workshop at FOSS4G NA 2016)

# TODO

- link TL presentation

# Solutions

1. Compute topographic index using r.topidx.

```
def run_slope(scanned_elev, env, **kwargs):
gscript.run_command('r.topidx', input=scanned_elev, output='topidx', env=env)
```

2. Compute topographic aspect (slope orientation) using r.slope.aspect and reclassify it into 8 main directions.

```
def run_aspect(scanned_elev, env, **kwargs):
gscript.run_command('r.slope.aspect', elevation=scanned_elev, aspect='aspect', env=env)
rules = ['45:135:1', '135:225:2', '225:315:3', '315:45:4']
gscript.write_command('r.recode', input='aspect', output='aspect_class', rules='-', stdin='\n'.join(rules), env=env)
# set new color table: green - yellow - red
gscript.run_command('r.colors', map='aspect_class', color='random', env=env)
```

3. Show areas with concave profile and tangential curvature (concave forms have negative curvature).

```
def run_curvatures(scanned_elev, env, **kwargs):
gscript.run_command('r.param.scale', input=scanned_elev, output='profile_curv', method='profc', size=11, env=env)
gscript.run_command('r.param.scale', input=scanned_elev, output='tangential_curv', method='crosc', size=11, env=env)
gscript.mapcalc("concave = if (profile_curv < 0 && tangential_curv < 0, 1, null())", env=env)
```

4. Derive peaks using either r.geomorphon or r.param.scale and convert them to points (using r.to.vect and v.to.points). From each of those points compute visibility with observer height of your choice a derive a cumulative viewshed layer where the value of each cell represents the number of peaks the cell is visible from (use r.series).

5. Find a least cost path between 2 points (for example from x=638360, y=220030 to x=638888, y=220388) where cost is defined as topographic index (trying avoid areas). Use r.topidx.

6. Compute erosion with spatially variable landcover and soil erodibility (use rasters cfactorbare_1m and soils_Kfactor from the provided dataset). Reclassify the result into 7 classes based on severity of erosion and deposition: