Pitney Bowes MapInfo Professional - Manual (Page 355)

• Opening a Registered Raster Image
• Opening an Unregistered Raster Image
• Opening a Georeferenced Raster Image
Registering the Coordinates of a Raster Image
Before you can overlay vector data on top of a raster image, you must first register the raster image so
that MapInfo Professional can position it properly in a Map window. In the Image Registration dialog
box, you can identify control point coordinates and specify the appropriate projection for the raster image.
Control points are the coordinates you identify on the raster image that MapInfo Professional can use
later to match up to other layers. It is very important to provide accurate control point information when
registering a raster image, so MapInfo Professional can display raster images without distorting or rotating
them. Later, when you overlay vector data, MapInfo Professional distorts and rotates the vector data so
both layers can line up properly. Identifying significant control points makes this match up process easier.
We suggest you use highway/street intersections and prominent landmarks as control points, as they
rarely move.
Specifying the correct projection of the raster image is also important for accurate display. Images that
do not have known projections, such as unrectified aerial photographs, are less suitable for use with
vector data.
There are two ways to register a raster image in MapInfo Professional. Each involves specifying the map
coordinates of control points on a reference map and matching them with equivalent points on the raster
image. To determine map coordinates, you can:
• Identify a point's coordinates from the paper map.
• Determine a raster images control point coordinates on screen and automatically transfer the information
to the Image Registration dialog box.
If you scanned in the image from a paper map, the map most likely contains a graticule (latitude
and longitude grid). You can choose those coordinates for prominent features and enter them
in the Image Registration dialog box. Note:
• For specific instructions, see Registering the Coordinates of a Raster Image and and Choosing Control
Points from an Existing Map in the Help System.
Reprojecting a Raster Map
From time to time, you will need to use a raster map registered in one projection in another map in
different projection. You can reproject the raster image, that is, change the coordinate system and the
way the raster image displays to accommodate the new vector map. Typically, the open map dictates
the projection of the successively displayed images. You can also reproject the raster using the projection
of a vector table.
Reprojecting a Raster based on a Vector Map
If you are working with registered raster data such as satellite and aerial photo images, scanned maps,
grids, seamless tables and WMS data, you might want to reproject that raster data to accommodate a
vector map.
MapInfo Professional performs the raster reprojection when you open a registered raster image inside
of an existing Map window with a different projection or when you change the projection of a Map window.
During the raster reprojection process, MapInfo Professional recalculates the pixel values of the source
image to make them display correctly in the destination image. In this resampling process, MapInfo
Professional tries to restore every pixel value of the image based on the pixels around it. In MapInfo
Professional there are two methods for calculating the pixel values of the destination image: Cubic
Convolution and Nearest Neighbor. These are industry-standard terms used by GIS professionals all
over the world. These methods are described later in this section.
355 MapInfo Professional User Guide
Chapter 13: Registering Raster Images