How to georeference your raster data

This article gives a detailed overview of the abilities and functions of MapTiler visual georeferences.

Where to find the georeferencer

Another name for this utility over the program is “Assign visually”. You can either enter it directly from the geographical location popup, in case you are trying to add a signle file in the raster processing mode, that is misssing this information.

mte-render-geolocation-missing.png

You can also access the tool apart of the loading files process from the geolocation menu in the files details panel.

mte-render-raster-input-assign-visually.png

How to georeference your image

To georeference an image, all you need to do is to select a sufficient number of points from two maps – your image and online map, to align them. The absolute minimum is three points, however, the more control points you assign, the more precise the result will be. The order doesn’t matter, you can first select a point in the online map and then on your image or vice versa.

The best choice is to pick points on different parts of the map and do it as accurately as possible: this can be accomplished by choosing corners of buildings, crossroads, peaks, and other clearly identifiable points. There is also an option to drop a point on one map and insert coordinates for the other one.

If you make any mistake during the whole procedure, you can always fix the wrongly inserted coordinate by clicking it on the map and either move it to the correct position or delete it.

How to change the basemap

Using the map switch you can select from the predefined basemaps or add a custom map service by pasting URL of WMS or TileJSON server. Here are the most popular options:

Use a Google basemap

  1. In the georeferencer, click Change basemap (the little globe icon). This opens a list of all available basemaps and the option to Add a custom map service.

  2. In the URL field, paste the URL of the Google basemap you want to add:

    • Roadmap: http://mt0.google.com/vt/lyrs=m&hl=en&x={x}&y={y}&z={z}
    • Terrain: http://mt0.google.com/vt/lyrs=p&hl=en&x={x}&y={y}&z={z}
    • Altered roadmap: http://mt0.google.com/vt/lyrs=r&hl=en&x={x}&y={y}&z={z}
    • Satellite only: http://mt0.google.com/vt/lyrs=s&hl=en&x={x}&y={y}&z={z}
    • Terrain only: http://mt0.google.com/vt/lyrs=t&hl=en&x={x}&y={y}&z={z}
    • Hybrid: http://mt0.google.com/vt/lyrs=y&hl=en&x={x}&y={y}&z={z}

  3. In the Type dropdown, change the map scheme to ZXY.

  4. Click Add layer. Your new basemap appears in the list of maps above; click on it to use it.

Other tools

The main window contains a search button in the very left top corner, which is a standard map search you know rom other map services. By typing the village name and clicking the search button the referencing map will zoom to the selected place. The autocomplete function is available.

Operation modes

On the top, you can switch between Side by side view and an Overlay, which is available when at least three points are selected on both maps. The coordinates button gives you an overview of already inserted points altogether with inaccuracy. Clicking on the coordinate will bring a selected point into central view, and hovering will highlight it. The clip option allows you to crop your image before publishing. This path is referred to as a clipping path or a cutline.

Coordinates input

When you click on both a map and a picture you are georeferencing, in the middle bottom part of the screen appears a small window with coordinates you can manually change. By clicking on the gear icon on the right, you can also select if the coordinates are shown in EPSG:4326 or WGS84 format.

Transformation type

The Gear icon on the top right corner gives you the option to change the way of transformation. All five available methods are described in a standalone manual.

View options

On the right bottom, you can find the lock icon, which grips both maps together and reproduce any move or zoom on one map on the other. The circle arrow straightens your image for viewing if it is distorted by georeferencing (this is just for easier orientation during the georeferencing process, it has no impact on the final product).

On this page