The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part Bl. Beijing 2008 
1256 
The different data formats (Data Tiles, Image chips, and 
Tracks) sort into this file system in specific manners. 
5.1 Data Tiles 
DEMs are provided in 1° x 1° degree tiles in geographic 
coordinates in Sun Raster Format. The various DEM sources 
plus additional data are organized as directory-trees from North 
to South and East to West in 1 degree steps. For resolutions 
below 1 arc-second the directory tree is further split up into 
0.01 degree tiles. For performance reasons each tile is held in 
lower resolutions as well. This enables an incorporation of data 
with fine resolution (e.g. height models from laser scanners) as 
well as quick access to data only available in relatively coarse 
resolution (e.g. GLOBE data). 
Data Tiles are provided in exact 1° x 1 Miles (geographic 
coordinates) in Sun Raster Format with DLR extension. The 
data is zipped prior to storage. As mentioned before, the various 
DEM sources plus additional data are organized in directory- 
trees from North to South and East to West in 1° steps, and for 
resolutions below 1° in 0.01° steps (fig. 6). The finest resolution 
supported is 0.01 arc-seconds. For performance reasons each 
tile of a fine resolution is held in coarser resolutions as well. 
For an overview of the resolution of the stored data tiles check 
table 1. 
Each tile contains an overlap of 30 arc-seconds to the South and 
the West to the adjacent tiles at the 1° x l°-directory level and 
an 0.3-arc-second-overlap at the 0.01° x 0.01 “-directory level. 
For the upper left and the lower right coordinate the pixel 
centers are annotated. As lower right coordinate the first 
coordinate outside the image is specified. For changing 
resolutions the tile border is kept, which means that the 
coordinates change in the different layers as well. 
Resolution 
(per pixel, 
in arc-seconds) 
File Size 
(in pixels) 
Directory 
Level 
30 
121x121 
l°x 1° 
10 
363 x 363 
l°x 1° 
3 
1210x 1210 
l°x 1° 
1 
3630 x 3630 
l°x 1° 
0.3 
121x121 
o 
O 
o' 
X 
0 
© 
© 
0.1 
363 x 363 
0.01° x 0.01° 
0.03 
1210x 1210 
o 
b 
0 
X 
o 
o 
0 
0.01 
3630 x 3630 
0.01° x 0.01° 
Table 1. Resolutions of data tiles provided in the database 
At the moment the following different elevation data with a 
global coverage are stored as Data Tiles in the database: 
• the GLOBE dataset (Hastings and Dunbar, 1998) with 
a global coverage and a resolution of 1km, 
• data from the Shuttle-Radar-Topography-Mission 
(SRTM) (Pessagno, 2000). SRTM mapped 58 million 
km 2 with DLR's X-band system and 119 km 2 of the 
land surface with NASA's C-band system within the 
56° Southern and 60° Northern latitudes, 
• data resulting from repeat-pass-interferometric DEM 
production with the ERS-1 and ERS-2 satellites, 
• a reference dataset used in the ground segment of the 
TerraSAR-X mission, composed of SRTM and 
GLOBE data. 
As the nature of the data has an impact on the requirements for 
the algorithms and consequently the design of an elevation 
model database the characteristics of the DEMs provided by the 
different sensors/missions is summarized in table 2. The 
accuracies to be provided by TanDEM-X are also listed. 
Source/Format 
Accuracy 
Resolution 
(in arc-seconds) 
relativ 
e 
absolute 
DTED-1 
20 m 
30 m 
1 
DTED-2 
20 m 
30 m 
1 
ERS 
20 m 
30 m 
1 
SRTM/C-Band 
8m 
16 m 
3 
SRTM/C-Band 
8m 
16 m 
1 
SRTM/X-Band 
6 m 
16 m 
1 
TanDEM-X 
2 m 
10m 
0.4 
Table 2. Resolutions and accuracies of different sources held in 
the database 
5.2 Image Chips 
Image chips are stored in the given directory structure (fig. 6). 
They are referenced by their center coordinate. Different from 
the data tiles they are only stored in their original resolution and 
not in the resolutions specified by table 1. Their resolution 
needn't fulfil any specification except for being specified in 
degrees or seconds. 
The directory structure has to be expanded by two components: 
• an identifier file ensuring a unique addressing of the 
image chips, 
• and a file containing a list where all image chips are 
tracked that are completely or in parts situated in the 
l°xl°- tile to guarantee a quick search for tiles. 
5.3 Tracks 
Tracks are also stored in the directory structure shown in figure 
6 and discussed in section 5.2. This structure is expanded by: 
• a file holding a unique number for assignment of new 
tracks during the import process, 
• a list of tracks situated in the specific tile, containing 
the unique identifier, the file name plus attributes that 
can be searched for, 
• a zipped file for each track. 
Tracks are not further referenced and are identified by their 
unique identifier, which is part of the filename. 
6. DATABASE ACCESS ROUTINES 
For each datatype (tiles, chips, and tracks) unique routines have 
to be foreseen allowing the import, export, inventory and 
maintenance of the data. 
6.1 Import 
For all data types exclusive write access is guaranteed by lock 
files. Log files are kept for a later reproduction of changes to 
the