Can someone point me to the precise method – algorithm and if possible, the maths – that MI uses for georegistration of raster images?
I am led to believe that the same process is used by GoldenSoft's Diger. As I understand it, MI uses some sort of proportionality without actually acting on the raster image on a pixel-by-pixel manner. The latter is sometimes called “warping" the entire image in order to georegister it according to control points; it involves converting each pixel’s spatial location into the correct projection for the map display. That's not what MI does. I assume that the MI registration results in the rendered screen display for the raster image being proportionally adjusted according to a simple algorithm. Since the screen display is some degraded rendered function of the raster from which it was derived, this is probably a much quicker operation than what I've described as "warping". Right or wrong? --- IL Thomas >From the MI 7.8 User manual, Chapter 13: Registering Raster Images Opening a Raster Image ---------------------- When you open a raster file, you need to know about a process called raster image registration. Using a vector map as a reference, you identify the coordinates of control points on the vector map and match them with equivalent points on the raster image. This coordinate information allows MapInfo Professional to determine the position, scale and rotation of the image so that you can overlay vector data on top of the image. The coordinate information is stored in a TAB file created during the registration process. The TAB file enables you to re-open the raster file in MapInfo Professional format. The registration process is explained in more detail in the next section. You usually register the image the first time you open it. However, you do not need to register the image if you do not plan to use vector data with it, or if it already contains georegistration information. Raster images usually fall into one of three categories: • A fully registered image, containing control points and a projection (e.g., GeoTIFF file). • A partially registered image containing control points, but missing a projection (e.g., an image with an associated World file). • An unregistered image missing control points and a projection. Once the image is registered, opening it again requires a slightly different procedure. Opening both unregistered and registered images is explained in the next section. -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.344 / Virus Database: 267.10.19/92 - Release Date: 7/09/2005 --------------------------------------------------------------------- List hosting provided by Directions Magazine | www.directionsmag.com | To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED] Message number: 17783
