Nowadays, it's common to find great orthophotos and satellite imagery on the Web. However, after downloading these (sometimes) large files, you might find that some don't have any georeferencing. Most likely these files are in an image format supported by Adobe Photoshop (e.g. JPG or TIF) and you can georeference it using the Geographic Imager Georeference tool.
These are the requirements to georeference an image:
- Knowing the coordinate system of the image (e.g. Mercator projection, State Plane system Alabama East, UTM system NAD 83 Zone 17 N..etc)
- Finding three or more points from the image to assign coordinate values to each of them. These points are known as ground control points.
You can bring your maps anywhere with our PDF Maps iOS app for iPhone, iPad, and iPod Touch. You can navigate your own map, locate yourself, make a note at the position collected, measure distances, and export and share the collected waypoints on a desktop or online application.
When transforming a world image, there may be artifacts created by the Geographic Imager transformation engine. Below are the results of a WGS84 world image transformed into a Stereographic projection.
When we zoom into the problematic area, you can see up close how some artifacts affect the image after the transformation was performed.
When transforming a world map in a geodetic system (such as WGS84) to a predefined projection (such as Robinson) using MAPublisher, the central meridian of the predefined projection should be set to 0 degree longitude as shown below.
Image 1: world map in WGS84
Image 2: world map in a predefined Robinson Projection
After importing a DEM file, you can always check the elevation value of a specific pixel in the Georeference dialog window. When you hover your mouse over the DEM image in the preview windw, you can get the image XY coordinate, latitude and longitude values, eastings and northing values (if the map is projected), as well as the elevation value.