Tutorial: Getting Started with Rasters

Introduction

FME supports reading and writing to over 70 raster formats. Additionally, there is a wide range of transformers that can alter raster data to match different requirements. This tutorial will explain a few basic examples, showing how to read, transform, and write raster data with FME.

Raster Concepts

FME Data Inspector or the Visual Preview window in FME Workbench are powerful tools for reading and viewing raster data. It is important to note that raster data is different from vector data. A raster image has no separate features, for example, houses, roads, or elevation points. The raster itself is a single feature. The perception of detail on rasters results from the different colored pixels. In the image below, two layers are shown: raster features and vector features. To a full extent, they may look identical; however, upon closer inspection, the vector features remain as identifiable building polygons no matter how far the data is zoomed in. In contrast, the raster features turn into chains of cells representing the buildings.

How FME displays raster data may vary from how it appears in other applications. In particular, some applications may apply an automatic contrast enhancement to a raster for display purposes so the raster doesn't appear black. FME Data Inspector does not apply any contrast enhancements. Because of this, the raster in FME Data Inspector may display as black occasionally if the data values are in a smaller range than is available with the full bit depth. FME does have ways to address this behavior, as described in this article.

Color vs Numeric Rasters

There is a distinction between a color and a numeric raster dataset. A color raster dataset is where each cell represents a color or grayscale (intensity) value - for example, a satellite image. A numeric raster is where each cell represents a numeric attribute for geographic elements covering a specific area - for example, a digital elevation model.

Raster Basics

Viewing and Inspecting Rasters

This example demonstrates how to view and inspect rasters in FME Data Inspector or Visual Preview in FME Workbench.
 

Raster to Raster

This example demonstrates how to convert from one raster format to another and reproject it to another coordinate system.
 

Raster Clipping

This example demonstrates how to use the Clipper transformer to clip a raster and change the black background (NoData band) to transparent (Alpha band).
 

Raster Tiling

This example demonstrates how to use the RasterTiler transformer to break up a raster into either a defined size or a number of tiles.
 

Raster Mosaicking

This example demonstrates how to mosaic multiple adjacent rasters together to create one image.
 

Removing Black Borders

This example demonstrates how to work with NoData and Alpha bands to remove a black border around an image.