Terrain Tiles on AWS Reader Parameters

General

Select the product type to read:

  • Terrarium (PNG): A 24-bit fixed point representation of elevation in meters, split over the red, green, and blue bands. To decode:

(red * 256 + green + blue / 256) - 32768

  • Normal (PNG): A 3-D vector representing the surface direction, and an 8-bit elevation value. The red, green and blue bands hold the x, y and z magnitudes, respectively. The alpha band contains quantized elevation data, with more opaque cells representing lower elevation.
  • GeoTIFF (GeoTIFF): Raw 16-bit integer elevation data in meters, suitable for analysis.
  • Skadi (SRTM HGT): 16-bit elevation data in meters, in unprojected WGS84 coordinates.

For more information on these tile formats, visit https://aws.amazon.com/public-datasets/terrain/.

Tile Resolution

Tile Resolution settings apply to Terrarium, Normal, and GeoTIFF. Skadi tiles are only available at one resolution, and are not in a projected coordinate system.

Due to the nature of the web map tiling scheme, terrain data is available at 16 different resolution levels. The zoom level can be chosen directly as an integer, or a minimum target resolution can be specified.

  • Zoom Level: This parameter is available when Resolution is set to Use Zoom Level. Select a zoom level from 0 (default) to 15 (where 0 is the lowest resolution, and 15 is the highest resolution). Tiles will be downloaded at the selected zoom level. Please note that tiles at higher zoom levels are oversampled from coarse source data.
  • Target (m/cell:) This parameter is required when Resolution is set to Use Target Resolution. Provided the requested resolution level is available through the service, data will have a resolution no more than the specified number of meters per cell (pixel). The Web Mercator system used for the Terrarium, Normal, and GeoTIFF formats is not equidistant, and has severe distortion at high latitudes. The target resolution specified here refers to the resolution in the coordinate system, rather than ground resolution.

Spatial Filter

Tiles can be selected individually or by search envelope. If both options are selected, the single tile will only be read if it is also within the search envelope.

Tile X/Y Index: The index of the tile to select.

For Terrarium, Normal, and GeoTIFF tiles, valid ranges will vary depending on the zoom level: at zoom level 0, the only tile is at x=0, y=0; at zoom level 15, valid indexes range from 0 to 32767.

For Skadi tiles, valid indexes range from -180 to 179 for X (longitude) and -90 to 89 for Y (latitude).

Envelope

Using the minimum and maximum latitude and longitude parameters, define a bounding box that will be used to filter the input features. Only features that intersect with the bounding box are returned.

If all four coordinates of the search envelope are specified as 0, the search envelope will be disabled.

Coordinates must be in LL84.

Advanced

Prior to FME 2022.0, web access through this format would automatically disable HTTPS Certificate verification when an SSL Error was received from the server. Now, this behavior must be explicitly enabled or disabled by this parameter.

The value of this parameter takes priority over the value of the Verify SSL Certificates parameter which might be defined by the Web Connection used with this format.

Schema Attributes

Use this parameter to expose Format Attributes in FME Workbench when you create a workspace:

  • In a dynamic scenario, it means these attributes can be passed to the output dataset at runtime.
  • In a non-dynamic scenario, this parameter allows you to expose additional attributes on multiple feature types. Click the browse button to view the available format attributes (which are different for each format) for the reader.