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How is the cache generated by ArcGlobe organized?

Last Published: April 25, 2020


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ArcGlobe is a paged display application that renders vector, raster, and elevation data by tiling it into geographic divisions (faces) and also tiling it recursively at varying levels of details (LOD), which is illustrated further in pages 3-5 of the "ArcGIS® 3D Analyst™ — Designing Interactive ArcGlobe Documents" whitepaper listed in the Related Information section below.

The data cache is a persisted representation of this technology that allows organization of visualization pages into a hierarchical file-based structure to facilitate paging in and out from the disk.

The cache structure consists of six global faces, four of which are equatorial faces, organized in the form of folders named T0, T1, T2, and T3, covering the geographic regions 180°W to 90°W, 90°W to 0°, 0° to 90°E, 90° to 180°E, and 45°N to 45°S, and two of which are ‘polar’ faces T4 and T5 covering 45°N–90°N and 45°S–90°S, respectively (see graphics on page 2 of the above whitepaper). Each globe data cache consists of these folders (T0-T5) only if the data set covers/crosses the particular face. Hence, a global dataset has all the faces (T0-T5), whereas a dataset for southern California, for example, only consists of T0 folder.

Each of the six major faces is subdivided into multiple tiles at different levels of detail. Each of these folders consist of visualization pages, or tiles, and each, again, is organized based on their geographic location (in the form of rows and columns) and resolution (LOD).

ArcGlobe supports many data types that could roughly be classified into three categories as far as the LOD classification is concerned: texture data (including feature data represented as rasterized), elevation, and vector (points, lines, 3D objects and billboard annotation). The LOD values differ depending on the data type. However, each successive LOD is derived by recursively dividing the previous LOD by four.

In ArcGlobe's data cache structure, the (LOD) for all texture data types begin with a L09. This folder corresponds to the lowest LOD, whereas L30 corresponds to the maximum level possible. Each level corresponds roughly to the scales listed in the table below. For raster/image data, these levels are primarily driven by the cell size (resolution) of the data.

Elevation data follows similar pattern as imagery, except its cache levels start from L08.

Data cache for imagery and elevation can be generated from the lowest possible LOD value to the maximum supported LOD (based on the cell size), hence the concept of ‘From’ and ‘To’ LOD values. When generating data cache, there is also the option to generate partial LOD ranges.

The LOD for vector data is solely driven by the ‘scale’ desired for visualization.

Vector data contains only a single LOD, hence only a single LOD folder for which the feature LOD (scale) value was selected for can be found. For example, if the ‘Feature Properties’ value of a vector data is set to ‘Counties’ (or at a scale of 1: 156543), it generates data tiles at a LOD of L06.

Raster LOD	Name			Scale 1				  Vector LOD	Resolution(meters)
9 Globe 10018754.17139462153829420444035 0 20000
10 Continent 5009377.085697310769147102220175 1 10000
11 Countries 2504688.5428486553845735511100875 2 5000
12 Country 1252344.2714243276922867755550438 3 2500
13 States 626172.13571216384614338777752188 4 1250
14 State 313086.06785608192307169388876094 5 612
15 Counties 156543.03392804096153584694438047 6 306
16 County 78271.516964020480767923472190235 7 153
17 Metropolitan area 39135.758482010240383961736095118 8 80
18 Cities 19567.879241005120191980868047559 9 40
19 City 9783.9396205025600959904340237794 10 20
20 Town 4891.9698102512800479952170118897 11 10
21 Neighborhood 2445.9849051256400239976085059448 12 5
22 City blocks 1222.9924525628200119988042529724 13 2.4
23 City block 611.49622628141000599940212648621 14 1.2
24 Buildings 305.74811314070500299970106324311 15 0.6
25 Building 152.87405657035250149985053162155 16 0.3
26 Houses 76.437028285176250749925265810776 17 0.15
27 House Property 38.218514142588125374962632905388 18 0.075
28 House 19.109257071294062687481316452694 19 0.0375
29 Rooms 9.5546285356470313437406582263471 20 0.0187
30 Room 4.7773142678235156718703291131735 21 0.0094

Article ID:000009955

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