GeoTIFF Reader Parameters

Connection

Source GeoTIFF Files or URLs – The GeoTIFF file or path to the COG file.

Dataset Parameters

This parameter allows you to choose different naming schemes for a feature type, and the number of feature types generated for the reader.

The Feature Type Name changes, depending on the selection.

Value Feature Type Name Example

From Format Name

<reader_type_name>

FORMAT_NAME

From File Name

<filename>

file

From Subdataset Name

<subdataset_name>

subdataset

From File Name and Subdataset Name

<filename_subdataset_name>

file_subdataset

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.

Spatial

Coordinate systems may be extracted from input feature data sources, may come predefined with FME, or may be user-defined. FME allows different output and input coordinate systems, and performs the required coordinate conversions when necessary.

How FME Processes Coordinate Systems in the Workspace

If a coordinate system is specified in both the source format and the workspace, the coordinate system in the workspace is used. The coordinate system specified in the source format is not used, and a warning is logged. If a source coordinate system is not specified in the workspace and the format or system does not store coordinate system information, then the coordinate system is not set for the features that are read.

If a destination coordinate system is set and the feature has been tagged with a coordinate system, then a coordinate system conversion is performed to put the feature into the destination system. This happens right before the feature enters into the writer.

If the destination coordinate system was not set, then the features are written out in their original coordinate system.

If a destination coordinate system is set, but the source coordinate system was not specified in the workspace or stored in the source format, then no conversion is performed. The features are simply tagged with the output system name before being written to the output dataset.

For systems that know their coordinate system, the Coordinate System field will display Read from Source and FME will read the coordinate system from the source dataset. For most other input sources, the field will display Unknown (which simply means that FME will use default values). In most cases, the default value is all you'll need to perform the translation.

You can always choose to override the defaults and choose a new coordinate system. Select More Coordinate Systems from the drop-down menu to open the Coordinate System Gallery.

Changing a Reprojection

To perform a reprojection, FME typically uses the CS-MAP reprojection engine, which includes definitions for thousands of coordinate systems, with a large variety of projections, datums, ellipsoids, and units. However, GIS applications have slightly different algorithms for reprojecting data between different coordinate systems. To ensure that the data FME writes matches exactly to your existing data, you can use the reprojection engine from a different application.

Note  To use this feature, you must have a supported GIS application installed on your system (for example, Esri ArcGIS®).

To change the reprojection engine, Select Workspace Parameters > Spatial > Reprojection Engine. In the example shown, you can select Esri (but the selection here depends on your installed applications):

For more information, see the links below:

A GeoTIFF file stores projection parameters in a set of keys. A key has an ID number ranging from 0 to 65535.

  • When the value is set to Yes and the ProjLinearUnitsInterpCorrectGeoKey flag is present in the file, the coordinate system offsets will be assumed to be in the linear units of the projection.
  • When the value is set to No or the ProjLinearUnitsInterpCorrectGeoKey flag is not present, the Offsets in Coordinate System Units parameter is used to determine the interpretation of the coordinate system offsets.
  • Yes – The coordinate system offsets stored in the GeoTIFF file will be interpreted as being in the linear units of the projection; this is correct according to the GeoTIFF specification.
  • No – The coordinate system offsets will be interpreted as being in meters; this is what is actually done in practice by many software packages.
Note  If the offsets are explicitly marked as being in the coordinate system units (via the ProjLinearUnitsInterpCorrectGeoKey flag in the GeoTIFF dataset), and Prefer File Coordinate System Units is set to Yes, this option is ignored.

By default, the GCP information is preserved as properties on the raster geometry.

If you select this checkbox, the GCP information, including a GCP projection, will be read from the file and applied to the raster data as an affine transformation.

GCP Interpolation Method

Specifies the interpolation method used to apply a GCP projection to the raster data.

  • Nearest Neighbor – Applies a projection based on the value of the pixel closest to the GCP. This method is the least resource-intensive, but also produces the lowest resolution GCP.
  • Bilinear – Applies a projection by averaging the closest 2x2 neighborhood of pixel values surrounding the GCP. This method produces higher-quality results than Nearest Neighbor.
  • Bicubic – Applies a projection by applying a weighted average of the closest 4x4 neighborhood of pixel values surrounding the GCP, with closer pixels weighted higher than farther pixels. Bicubic interpolation requires the most amount of processing time.

A search envelope (also known as a bounding box) is a rectangular area that defines a geographic area. In FME, the easiest way to define a search envelope is to use search envelope parameters.

Defining a search envelope is the most efficient method of selecting an area of interest because FME will read only the data that is necessary – it does not have to read an entire dataset. Search Envelope parameters apply to both vector and raster datasets and can be particularly efficient if the source format has a spatial index.

Most FME readers have parameters to define the search envelope of data that is being read:

Screenshot with blank search envelope min and max x and y parameters

The parameters include the x and y coordinates of the bounding box as well as a parameter that defines the coordinate system.

How to Define the Bounding Box

Using the minimum and maximum x and y parameters, define a bounding box that will be used to filter the input features. Only features that intersect with the bounding box are returned. Note that the bounding box intersection is not a full geometry intersection (based on spatial relationships) that would be returned by a transformer like the SpatialFilter.

Note  If all four coordinates of the search envelope are left at 0, the search envelope will be disabled even if this option is checked.

Search Envelope Coordinate System

Specifies the coordinate system of the search envelope if it is different than the coordinate system of the data. The coordinate system associated with the data to be read must always be set if this parameter is set.

If this parameter is set, the minimum and maximum points of the search envelope are reprojected from the Search Envelope Coordinate System to the reader’s coordinate system prior to applying the envelope.

Clip to Search Envelope

The underlying function for Use Search Envelope is an intersection; however, when Clip to Search Envelope is checked, a clipping operation is also performed.

  • When left unchecked (set to No), features that overlap the boundary will be included in their full (unclipped) form.
  • When checked (set to Yes), this option instructs FME to clip features to the exact envelope boundary. FME removes any portions of imported features being read that are outside the search envelope.

Clip to Search Envelope: No

Clip to Search Envelope: Yes

Any features that cross the search envelope boundary will be read, including the portion that lies outside of the boundary.

Any features that cross the search envelope boundary will be clipped at the boundary, and only the portion that lies inside the boundary will be read.

The search envelope includes the bounding box and the extent of the raster.

The search envelope includes only the area within the bounding box.

The raster size will still match the bounding box, but the area without data will be filled with Nodata values to represent the absence of data, if the source raster has them.

Raster Nodata may be a single value across all bands, a single value per band, or a separate alpha or transparency band that indicates the lack of data values (this is more common in images than other types of rasters).

Advanced

When a GeoTIFF file contains pyramids (reduced-resolution images), this parameter specifies the pyramid level to read.

Pyramid level 0 represents the original raster data. Values greater than 0 represent a reduced-resolution image.

Note  The GeoTIFF format does not guarantee that the levels are ordered. For example, pyramid level 2 may have more rows or columns than pyramid level 1, or vice versa.

GeoTIFF contains a “raster type” key which specifies whether each pixel in the file represents an area (“PixelIsArea”) or a point (“PixelIsPoint”).

When reading PixelIsPoint data, by default, the raster extents is shifted up and left by half a pixel when transformed to the FME georeferencing model. Setting this value to Yes prevents this adjustment from happening.

Specifies whether to scale values for color bands that are a non-standard bit depth (that is, not 8 or 16).

  • Scale to Standard Bit Depth – Values will be scaled to a standard bit depth (that is, 1-7 bit bands will be scaled to 8 bits, and 9-15 bit bands will be scaled to 16 bits).
  • Do Not Scale – Values will be left unchanged. 
    Note   Selecting Do Not Scale may result in images appearing very dark when viewed in the Data Inspector.

Use Network Authentication

Specify the authentication method to use when accessing a password-protected server.

  • Basic (default) – Basic access authentication is designed to allow a client to provide credentials to a server on the assumption that the connection between them is trusted and secure. Note that any credentials passed from client to server can be easily intercepted through an insecure connection.
  • NTLM – A challenge-response protocol that is used to provide compatibility with versions of Windows earlier than the Windows 2000 operating systems.
  • Web Connection – Web connections provide a convenient and secure way to store and reuse previously established connection parameters. See Web Connection below.
Note  To access datasets using a proxy server, use the Network tools in FME Options. From the FME Workbench menu, select Utilities > FME Options > Network Proxy. For more information, see Network Proxy in FME Workbench Help.

Using Web Connections

FME Options: Web Connections