The standard method of identifying morphometric 
features is to pass a local (usually 3by3) window over the 
DEM and examine the relationship between a central cell 
and its neighbours, and on the other hand through a water 
flow analysis over a DEM (Rieger, 1992) 
Pits identification process comes to drainage basin 
identification process where the lowest point of basin and 
outflow point are not the same. In this case the lowest 
point is pit base. The basin identification algorithms 
involve a ‘basin climbing’ approach where a basin 
outflow point is identified and the basin is recursively 
'climbed' until all points flowing from the drainage divide 
have been covered. 
Fig.l. Pit identification process 
There are a number of possible solutions to remove pits 
from DEM. This may be achieved by either ‘excavating’ 
cells that connect the base of a pit to its adjacent 
downstreambasin, or by flooding pits until outflow is 
redirected. The first method is applied here because of 
several reasons: 
The results of processing are linear features (sinks) that 
may be well included in the interpolation as form lines. 
The impact of vegetation heights, which are not filtered 
out in the preprocessing stage, is greatly eliminated. 
3.1 Laying the pitpath 
According to the definition, pitpath is such a path that 
starts on a pit base, goes upwards through outflow point 
and flows away to its adjacent downstreambasin. It has to 
be set in such a way that it passes downwards by its 
whole length, (much more details about lying pitpath can 
be found in Rieger, 1992) 
Fig.2. Pit removal process 
4. The practical implementation 
The methods of geomorphological improvement of 
DTMs based on laser-scanner data are still under test, and 
here is only a pit removal introduced. 
As test area an area of 91 km2 in Vienna Woods was 
taken. The company TopScan Germany made the data 
acquisition through an airborne laser scanner ALTM 
1020 of Optech Inc. Canada. The whole dataset contains 
about 9275000 laser points. The mean distance between 
points was 3.1 m. The Institute for Photogrammetry and 
Remote Sensing produced DTMs for 360 map sheets at a 
scale of 1:1000. The DTM has a grid width of 3.125m 
resulting in 160x160 grid meshes pro one sheet. More 
details about this project can be found in Kraus (1997) 
and Kraus et al. (1997). 
As test dataset, the final DTM was taken according to the 
new method of interpolation and filtering described in 
Kraus 1998. By means of program system MATRIX 
originally developed by Dr. Wolfgang Rieger, yet partly 
adopted for XX-lfamework in SCOP, the pure raster 
elevation model was calculated at a resolution of 1 m. For 
visualization purposes shading and contouring are 
performed. 
Test of a new method was done over an area where as 
many morphometric features as possible can be found 
within a small area. The Fig .3 shows such an area that 
comprises several catchment basins that collect water into 
their valleys.