Raster Meets Vector Data - Open Source Geospatial Tools: Applications in Earth Observation - page 136

As a more advanced example, we add new contour lines with different intervals
in the same Spatialite vector dataset. We use a loop in Bash to iterate over a variable
H that represents the contour densities. As we already created a contour vector for
10m intervals, we start with 20 m and end with 100 m in steps of 10 m. The result
is stored in a temporary Spatialite vector dataset. At each iteration, the temporary
vector dataset is added as a new layer to the vector st-helens.sqlite using
ogr2ogr . The new layer name equals the height interval. The DSMand the contours
for the height intervals H =30 m and H =100 m are shown in Fig. 9.3 .

for ((H=20;H<=100;H+=10));do
gdal_contour -3d -a height -i $H -nln $H -f SQLite
→ st-helens_dsm_10m.tif st-helens_$H.sqlite
ogr2ogr -update -nln $H st-helens.sqlite st-helens_$H.sqlite
rm st-helens_$H.sqlite
done

59 m. At the finest detail
( H=10 ), 1,372 contour lines are created for all connecting pixelswith values between
1126.21 and 1136.21, 1136.21 and 1146.21,

The height of the DEM ranges from 1116.21 to 2538 .

Similarly, for H=20, 690 contour
lines connect pixels with values between 1136.21 and 1156.21, 1156.21 and 1176.21,
etc. For the maximum interval of 100 m, there are 142 contour lines. The maximum
height in the DSM is 2538

...

. 59 m.