Quantitative Analysis of the Digital Elevation Models Generated with IDW Algorithm of Changing Power

Fahmy F. F. Asal
Page No. 53-64

This research applies quantitative analysis techniques on DEMs generated using the Inverse
Distance Weighting (IDW) interpolator of different powers in order to examine the effects of the
variation of the power on the accuracy of the elevations extracted from that DEMs. Real elevation
data has been collected from field using ground surveying techniques with a total station instrument
in a hilly corrugated terrain. DEMs have been generated from the elevation data at a unified grid
cell size using IDW interpolator with varying powers starting from a power of one and ending by a
power of ten. Quantitative analysis has been carried out on the DEMs using three different testing
and analysis techniques; evaluation of the contour-line maps of the difference between DEMs,
analyzing profiles extracted from the DEMs, then performing accuracy assessment of the extracted
elevations from the DEMs using independent external checkout measurements. The analysis has
shown that IDW faces difficulty in interpolating elevations in highly corrugated areas however; the
interpolation operation improves with increasing the power of the IDW till the power of four. Also,
at breaklines IDW with power of one faces the maximum difficulty in estimating elevations with a
tendency of smoothing and approximating the DEM. Additionally, the maximum differences
between profiles extracted from lower power DEMs and those from higher power DEMs have been
at the corrugated parts of the terrain while at gentle terrains the profiles from different DEMs run
close to each others. Finally, the accuracy of the DEM records the maximum improvements (about
95%) when changing from the power of one to the power of two.
Key words:- DEM/DTM/DSM, Ground Surveying, IDW, Digital Mapping, Spatial Accuracy