Applying OLAP Pre-Aggregation Techniques to ... - Jacobs University

42 3. Fundamental Geo-Raster Operations
(a) Grey 8-bit raster A (b) Grey 8-bit raster B (c) Output raster image
Figure 3.3. Cells of Rasters A and B with Equal Values
Reclassification
Reclassification is a generalization technique used to re-assign cell values in classified
rasters. For example consider the query below where reclassification is based on a land
suitability study.
Query 3.2.4. Given an 8-bit gray image A, map each cell value to its corresponding
suitability class shown in Table 3.2 1 , and decrease the contrast of the image according
to the decreasing factor.
The query can be answered as follows:
MARRAY sdom(A),g (((A[g] > 180) ∗ A[g]/2) +
Results are shown in Fig. 3.4.
(((A[g] ≥ 130)and(A[g] < 180)) ∗ A[g]/3) +
(((A[g] ≥ 80)and(A[g] < 130)) ∗ A[g]/4) +
((A[g] < 80) ∗ A[g]/5))
1 Classification taken from http://www.fao.org/docrep/X5310E/X5310E00.htm