Once the coordinate system is specified for your picture, you can already set the geographical position. By this, you define where exactly your picture is located on the planet. This transforms a picture into the map.
In the best case scenario, the geographical position system was already set previously by external software and MapTiler automatically loads it. If it is not known, you have few other options how to georeference your image:
Assign Location Visually (Georeferencer)
This is the most common situation for scanned maps, photos from your drone or other materials captured by you. All you need to do is select a few points on the already published map as well as on your image.
The minimum is three points, but the accuracy increases by selecting more. The best choice is to pick points on different parts of the map and do it as accurate as possible: this can be accomplished by choosing corners of buildings, crossroads, peaks and other clearly identifiable points.
The whole process is in detail described in this tutorial, common usage can be seen in this video:
Load from external file
If you are working with previously processed files, some of them have already position saved in the external files. Usually, these are with extensions .wld, .tfw, .jgw, .pgw, .gfw, or exported from GIS software such as OziExplorer or MapInfo (extensions .map, .tab). If you have such a file, just click on the import button, choose the file, confirm, and the Georeference will be loaded.
Specify Bounding Box
In the situations where coordinates of the map corners are known, you can use Specify Bounding Box option that creates a border of the map itself. The Bounding Box has to be specified in this order: West, South, East, North. Default value -180 -90 180 90 covers the whole world. Corners coordinates can be easily set by Bounding Box Tool. Assigning a position via bounding box is illustrated in the following tutorial:
Geotransformation defines the position of an image by one corner position, the scale of the image and its rotation. The format for geotransformation is “posX scaleX rotX posY rotY scaleY” with spaces between numbers.
- posX - the X position of the corner (mostly coordinate of the top-left one)
- scaleX - resolution of the X line (in most of the cases this is the West-East pixel resolution)
- rotX - rotation of the X line (in case of unrotated images, this value should be 0)
- posY - the Y position of the corner (again, mostly coordinate of the top-left one)
- rotY - rotation of the Y line (in case of unrotated images, this value should be 0)
- scaleY - resolution of the Y line (in most of the cases this is the North-South pixel resolution - should be a negative value)
This option defines map position by position of the corners. You need to enter three pairs of number, each specifies one corner of the map – the first one is the top-left corner, followed by the top-right corner and the last one is bottom-right. The format of coordinates is “east1 north1 east2 north2 east3 north3” with space between the numbers.
Corners can be visually set and copy & pasted from external services.
In case you are still not 100 % happy with the result or there are some doubts, you can step back by clicking on “Change” button and repeat the whole process.
Once the result is appealing, click on the “Continue” button and go for one of the offered saving options.
For command-line georeference options, see the MapTiler manual.