WebMapTiler
From fmepedia
See VirtualEarthHTMLCreator page for an example with this transformer.
| Table of contents |
Basics
The WebMapTiler creates a series of image tiles in a form that can be utilized by Virtual Earth or other web mapping application. This is done by resampling rasters to various different resolutions and then splitting them into tiles. This transformer produces similar output to the MSR MapCruncher utility.
This transformer accepts only raster features and is unaffected by raster band and/or palette sub-selection.
Maximum Zoom Level
The Maximum Zoom Level parameter specifies the maximum zoom level for which tiles will be generated, from 1 (coarse) to 23 (fine). Level 1 is the lowest level of detail; at that level, the entire world map is 512 x 512 pixels. Each level increases the number of rows and columns by a factor of two: level 2 is 1024 x 1024, level 3 is 2048 x 2048, etc. Level 23 is the highest level of detail.
If this parameter is unspecified, the maximum zoom level will default to the smallest zoom level that the resolution of the original raster would support.
Interpolation
Cell values are interpolated in order to change the raster to the specified size. The choice of interpolation methods is:
- Nearest Neighbor
- Bilinear
- Bicubic
- Average 4
- Average 16
Nearest Neighbor is the fastest but produces the poorest image quality. Bilinear provides a reasonable balance of speed and quality. Bicubic is the slowest but produces the best image quality. Average 4 and Average 16 have a performance similar to Bilinear and are useful for numeric rasters such as DEMs.
Quadkey
The Quadkey Attribute specifies the attribute in which the quadkey of each tile should be stored. Virtual Earth quadkeys uniquely identify a single tile at a particular level of detail. Generally, when writing out the rasters generated through this transformer, one would fanout the destination feature type on this attribute. The PNG writer is recommended for the best results.
Raster Index
If a Raster Index Attribute is specified, an attribute will be added to each output feature that identifies which raster it was created from. This index is zero-based, so all tiles created from the first input raster will have a value of 0, all tiles created from the second input raster will have a value of 1, etc.
Coordinate System
This transformer will accept only features that are in the EPSG:3785, EPSG:900913 or SPHERICAL_MERCATOR coordinate systems. All features must be reprojected into one of these coordinate systems prior to entering this transformer.
EPSG:3785 is known as "Web Mercator". It is the coordinate system used by Virtual Earth and Google Earth.
