If you want to use a raster map image in a GIS program, it needs to be calibrated so that the software will know the geographic position of every pixel in the image. This calibration data can be embedded in the file, as in GeoTiffs and MRSID files, or external as in worldfiles. If you have a raster map image which doesn’t include this calibration data, you’ll need to create it yourself; this process is called “image registration” or georeferencing. There’s a number of free programs that can perform this function, and I’ve put together a list of some of them below; if you know of others, please let me know and I’ll add them. And if I’ve included a program that doesn’t do georeferencing (very possible, since I haven’t used all of them), let me know that as well and I’ll drop it from the list.
One thing to keep in mind: some of the programs only work correctly if the map image is already in a specific map projection like UTM or geographic, and you use the same coordinate system to georeference the image. As a general practice, it’s always best to use the same coordinate system the map was created in to georeference it. For example, if you have a map in the UTM projection, and use geographic coordinates to georeference it, the resulting calibration is unlikely to be accurate over the entire map (unless you’re at the equator). Some programs let you warp the map image to get it to match the coordinate system, a process known as “rubber-sheeting”; this is especially useful for those maps that aren’t drawn accurately, like old or hand-drawn maps, or maps created in no-longer-used coordinate systems.
BTW, I haven’t used most of these for georeferencing – GlobalMapper is my program of choice for this function. It’s not free, or even cheap, but it works great for georeferencing, including rubber sheeting. For beginners, I’d suggest looking at MapWindow, qGIS or MicroDEM first before going on to the more advanced software.
MicroMSI (link may be dead)
Online map rectification tools
Map Maker Gratis can also do georeferencing (of course, Map Maker Pro also)
Which of these run on Mac OSX?
Thanks
Off the top of my head: gvSIG, qGIS, OSSIM, Hypercube, GRASS and Landserf. One or two of the others might be Mac-compatible as well.
instead of global mapper, one of the best georeferencing programs is surely ERDAS IMAGINE. once you have worked with it, and its different error calculation functions, you recognize that usual GIS georeferencing is really not very accurate. anyway they to the job for an easy and fast georeferencing. nice list, thanks.
How about Google Earth’s image overlay feature which can be saved as KMZ?
You can also add the Orfeo Toolbox (OTB) to the list :
http://www.orfeo-toolbox.org
There is image georeferencing, image to vector data registration, etc.
For QGIS is plugin MapSheetAutoGeoRef that helps fast georefferencing large raster datasets.
Maybe Microsoft Research MapCruncher
http://research.microsoft.com/en-us/um/redmond/projects/mapcruncher/
is also of interest. It provides capabilities for
– registering scanned papers (e.g. pdf, tiff – not geotiff, etc.) against Bing Maps (formerly known as Virtual Earth)
– tiling the input map into a tile scheme conforming to Bing Maps.
This list is extremly useful, thanks for that. Our team has a few raster-based hydrological datasets hidden somwhere in our common G:, yet these never got referenced. I will definetly show this posting to our GIS guru on Monday and hope he might get a feeling to try out some of these products.
Thanks foor the list Guys
Add NEST to the list http://www.array.ca/nest