TWELVE DIFFERENT INTERPOLATION METHODS: A CASE STUDY 
OF SURFER 8.0 
Chin-Shung Yang*, Szu-Pyng Kao*, Fen-Bin Lee**, Pen-Shan Hung** 
*National Chung Hsing University, Taichung, Taiwan, ROC yangchin@ms |.emax.net.tw 
**Feng Chia University, Taichung, Taiwan, ROC 
majorlfp@mail.apol.com.tw 
KEY WORDS: DTM (digital terrain model), Interpolation 
ABSTRACT 
SURFER is a contouring and 3D surface mapping program, which quickly and easily transforms random surveying 
data, using interpolation, into continuous curved face contours. In particular, the new version, SURFER 8.0, 
provides over twelve interpolation methods, each having specific functions and related parameters. In this study, the 
5 meter DTM was used as test data to compare the various interpolation results; the accuracy of these results was 
then discussed and evaluated. 
1. INTRODUCTION following paper, we will introduce every 
How to adequately use exist numerous interpolation method in SURFER. 
wide-distributed height points has been an important 2. SURFER INTERPOLATION METHODS 
topic in the field of spatial information. Normally, 2.1 The Inverse Distance to a Power method 
contouring is the way to accurately describe the The Inverse Distance to a Power method is a 
terrain relief by means of Scenography, Shading, weighted average interpolator, which can be either 
Hachure and Layer Tinting in a way which is best fit exact or smoothing. With Inverse Distance to a 
to the habit of human vision. Power, data are weighted during interpolation, so 
Presently, discretely collected height points have to that the influence of one point, relative to another, 
be interpolated to form curved faces, the selection of declines with distance from the grid node. Weighting 
spatial interpolation methods decide the quality, is assigned to data through the use of a weighting 
accuracy and follow-up analysis applications. power, which controls how the weighting factors 
Interpolation methods are used here to calculated the drop off as distance from the grid node increases. 
unknown heights of interested points by referring to The greater the weighting power, the less effect the 
the elevation information of neighboring points. points, far removed from the grid node, have during 
There are a great many commercial interpolation interpolation. As the power increases, the grid node 
software, however, most of them are tiny and value approaches the value of the nearest point. For a 
designed to solve specific problems with limited smaller power, the weights are more evenly 
versatility. The SURFER is a software developed by distributed among the neighboring data points. 
US GOLDEN company, and the newest version 8.0 Normally, Inverse Distance to a Power behaves as an 
contains up to 12 interpolation methods to been free exact interpolator. When calculating a grid node, the 
chosen for various needs. Users are suggested to first weights assigned to the data points are fractions, the 
have the basic understanding of every interpolation sum of all the weights being equal to 1.0. When a 
methods before he or she can effectively select particular observation is coincident with a grid node, 
parameters in every interpolation methods. In the the distance between that observation and the grid 
778 
Interna