We make a screenshot of a map we see on the web that covers the whole world, from +/- 90 degrees of latitude and +/- 180 degrees of longitude. The image shows the position and geology of continents as they were 200 million years ago. We georeference the image using four control points placed at the +/- 90 degrees and +/- 180 degrees corners, using a target map with a Bing streets background layer. We use the Show Coordinates option in the Register pane to quickly set exact target control point locations. As a bonus, we show how to knock out "background" pixels if our image is a palette image. For details on georegistration, see the Register Pane topic.
See the video version of this topic in the Georeference a Whole World Image video.
Windows and panes in this topic are shown undocked. To undock or dock a window, shift-click the window's tab when docked and shift-click the window's caption bar when it is undocked.
We visit a website and see an image of a map that we like. We can either download the image or make a screenshot, creating an image stored in a file called Geology200.png. Using File - Import we import the .png image into Manifold.
In the Project pane, double-click the Geology200 image to open it.
The result shows the screenshot we made. We have used a graphics editor to trim everything else from the image except the extent of the image showing the map. The map is intended to cover the entire Earth, extending over +/- 90 degrees of latitude and +/- 180 degrees of longitude.
We need a target map to which we will georegister the image. Because we intend to edit control point coordinates, we want our map to use Latitude / Longitude so the coordinates we edit are values in degrees.
We choose File - Create - New Map.
In the New Map dialog we press the coordinate picker button and choose Latitude / Longitude from the list of favorites. We will use Bing streets as the Base layer.
We do not check the box for the Geology200 image, as we do not want to use that as a layer in the new map.
Press Create Map.
That creates a new map in the Project pane, which we will use later.
Commands in Manifold apply to whatever window has the focus.
We click on the open Geology200 image window to ensure the focus is on that window.
In the pull down menu for the cursor mode button, we choose Edit Control Points.
That switches the mouse cursor into Edit Control Points mode. All navigation moves, like clicking and dragging to pan or right-clicking and dragging to zoom box still work. We right-click and drag to zoom into the upper left corner of the Geology200 image.
Click on the corner to place a control point there.
A new control point, automatically named P 1 appears.
The Register pane automatically opens as well, and the new control point appears in the list of control points.
We can use the Back button on the main toolbar to go back to a zoomed out view, and then right-click and drag to zoom box into the next corner where we would like to place a control point.
We place four control points, one at each corner of the image.
As we place each control point, it will be added to the list in the Register pane, automatically named in sequence. We can change the names if we like by double-clicking into a name, but since the default names are convenient, we leave them as is.
Leave the Geology200 window open. If we close the window, we lose the control points we have assigned. If we would like to close the window without losing the control points we have marked, we should first save the control points, as discussed in the Register Pane topic, so they will be available to be loaded when we open the window again.
We now will mark corresponding control point locations in the map.
Double-click the Map in the Project pane to open it in its own window.
With the focus on the map window, the Register pane starts off blank. In the pull down menu for the top box, instead of (current window) we choose Geology200 as the source of control points. Instantly, the Register pane fills with control points taken from the Geology200 source window, and the pane configures itself for using the map window as a target window.
In the pull down menu for the cursor mode button, we choose Edit Control Points.
That switches the mouse cursor into Edit Control Points mode.
Click anywhere near the Northwest of North America to place a control point there. A rough location is fine, since we will precisely specify the position for the control point later by entering the desired coordinates.
A new control point location appears, automatically assigned to control point P 1.
Control point P 1 in the list shows a + icon to indicate it is marked, and the on/off box also enables, since now there is a control point location marked that can be turned off and on.
The table cursor automatically moves down one row, so the next location we click will be that for the P 2 control point.
We click three more times to mark approximate locations for the remaining control points. Note that when we click, we should click in the order corresponding to the locations used for control points in the Geology200 window. That is, we click in the Northeast of the image for P 2, then down and to the left for P 3 and finally down and to the right for P 4.
As we click control point locations, the list in the Register pane fills in.
Pressing the list style button allows us to change how control points are listed in the Register pane.
We press the list style button and choose Show Coordinates.
That switches the list to displaying the coordinates of each control point location. The list uses whatever are the native coordinates for the window. That is why we created the map using the Latitude / Longitude coordinate system, so the control point coordinate locations are given in degrees.
We can edit the location of a control point by double-clicking into a coordinate box and change the value to what we want, pressing Enter to commit the edit. For example, we can change the value of the longitude (X) coordinate for the P 1 control point to -180.
We change the values for coordinates for all the control point locations to even +/- 90 degrees latitude and +/- 180 degrees longitude, corresponding to their desired locations precisely in the corners of the Latitude / Longitude coordinate system.
As we change the values of the coordinates, the control points automatically move accordingly.
We are now ready to georegister the Geology200 image. We choose thin-plate spline as the Method.
A good Render option for RGB images is forward, average. However, that option should not be used if pixel values should not be averaged, for example, when georegistering palette (indexed) images or images where pixels represent classification codes.
Press Preview to see a preview, if desired.
The preview appears in shades of blue preview color.
To georegister the Geology200 image, press Register.
A new image, called Geology200 2, and its table appear in the project pane. We can rename that image as we like.
Dragging and dropping the new Geology200 2 into the map, we see it is indeed exactly georeferenced.
It may be more convenient to work with images that are palette images, also known as indexed images, because in those images it is very easy to replace colors. For example, if our Geology200 image was a palette image, we could easily replace the gray color used for ocean areas with transparent colors, so the continents as they were 200 million years ago could be seen against a modern background.
In what follows, we assume the Geology200 image was imported from a .png file where it was stored as a palette image. It therefore imports as a palette image in Manifold, as well.
We mark control points as before, doing that before we assign transparent color to gray pixels, so that the corners are more easily visible when we zoom in to place control points.
When we pop open the Style pane for the Geology200 palette image, we see the various colors that are used. We double-click onto the color well for the gray color we think is the color used for ocean pixels.
We change that color well to transparent color, and then we press Update Style.
That instantly "knocks out", that is, renders transparent, all pixels that used that gray color. We see we guessed right about which color well was the gray color to make transparent, as pixels for ocean regions have disappeared, now being transparent.
We assign control point locations in the target map as before, using the Show Coordinates list style to change the coordinates of the control points to even +/- 90 degrees latitude and +/- 180 degrees longitude values.
To georegister the palette image, we must change the Render option to forward, nearest, since that option preserves exact pixel values and does not average them or otherwise interpolate between exact pixel values.
Dragging and dropping the resulting georeferenced image into the map, we see how the transparent pixels allow the underlying layer to show through.
Zooming in, we can see how the continents were arranged 200 million years ago.
A different choice of background layer, such as Bing satellite, may provide a more readable scene.
This example uses a screenshot of a map in a browser as an example raster image to be georegistered, but the workflow we have used works with any raster image that shows a map intended to cover the whole world, from +/- 90 degrees of latitude and +/- 180 degrees of longitude.
Higher resolution? No problem - We use a screenshot as a starting image to make it clear there is no coordinate system of any kind assigned to the starting image. But screenshots are intrinsically low resolution images, only as many pixels as appear on a monitor. This same method works exactly the same if we start with a much higher resolution image, such as a high resolution scan of a paper map, or a much higher resolution image created in a graphics arts package.
A rose by any other name - Manifold uses one word, georegistration, to refer to the same process that is used for both raster images and vector drawings. Manifold uses the same Register pane and the same workflow for both rasters and vectors. ESRI uses two words, and two significantly different procedures, depending on whether a raster image or a vector drawing is being georegistered. ESRI uses the word georeferencing when applied to raster images, but spatial adjustment when applied to vector drawings. Georegistration and georeferencing are synonyms in Manifold.
5 Minute Tutorial - Georegistration - In just five minutes we learn how to georegister (georeference) a vector drawing with an unknown coordinate system to a known-good map. Georegistration is a key capability that allows us to cast raster images and vector drawings into geographic context, so they can be used as GIS layers in maps. We can georegister aerial photos and drone photos, scan paper maps and georegister those for use in GIS, we can georegister CAD drawings, and we can rescue vector drawings and raster images that once had coordinate systems but were published in formats that failed to preserve coordinate systems. Super! Works in the free Viewer, too.
5 Minute Tutorial - Georegister a Drone Photo - See the fast and easy way to georeference drone photos for use in GIS and online web mapping: Learn how to georegister (georeference) a drone photo to line up with Google imagery for full GIS use and for use within Google Maps and other web mapping applications. This video uses exactly the same drone photo used in ESRI's ArcUser example of how to georeference a drone photo in ArcGIS Pro. The difference is that using Manifold is faster and easier.
5 minute Tutorial - Georeference Many CAD Layers - Georeferencing CAD layers is a common task in any GIS. Manifold makes it a lot easier with fast, simple workflow that avoids extra effort and lets us recycle what we've already done. This video shows how we can add a few control points just once and then georeference an entire stack of CAD layers imported from a DWG without adding more control points or repeating any work.
Georeference a Scanned Paper Map - In only five minutes of actual work we use Manifold to georeference a 157 MB scanned paper map so it can be used as a layer in GIS. The scanned map is a historic map showing Davy Crockett National Forest in Texas, downloaded from the Library of Congress website.
Georegistration - Save and Load Control Points - Georegistration (georeferencing) in Manifold uses control points to match features visible in the raster image or vector drawing to be georeferenced with corresponding features visible in a known-good reference. This video shows how with a single click we can save or load control points. Because Manifold saves control points as ordinary vector drawings, we can take advantage of that to make mass changes to control points if we like. In the video we use two versions of a scanned map, one with a gap in the middle and in the other where the gap is closed. Control points that were placed in the version with a gap can be easily adjusted, dozens at a time, for use in the other version, saving a lot of repeated work.
Georeference a Historic Map using a List of Cities - Georeference a scanned paper map downloaded from the Library of Congress that shows slave populations in Southern States in the 1860 census. The scanned map shows locations of cities, which we will use as control points. We create a drawing to quickly mark the locations of cities in the scanned image. Next, we download a modern map of cities in the US and their locations. We can use the list of cities in the modern map as a source of control points for the target, saving us from having to enter them manually. Manifold automatically matches names, ignoring those that are not needed, from the modern map during the georegistration process.
Georeference a Whole World Image - See how to georeference an image scraped from the web that shows the geology of continents as they were 200 million years ago.
We mark four control points in the image, then we roughly mark four corresponding control in a Manifold map using Bing as a background layer. In the Register pane we edit the coordinates of those control points to be even +/- 90 and +/- 180 degrees, and then we press Register. Done! The video also shows how we can import and georeference a second image similar to the first, without needing to add any control points, just re-cycling the ones we created before.
Example: Georegister a Drone Photo - We take a raster image, a drone photograph in Everson, Washington, that was imported from an ordinary .jpg file, and we georegister it using a map that shows a Google Satellite view of the same region, casting the drone photo into Pseudo-Mercator projection. We use previews to see how well the control points we have added will work, before creating a georegistered image.
Example: Georegister a Vector Drawing - We take a vector drawing with an unknown coordinate system that shows the provinces of Mexico and we georeference it to a map containing a Bing Streets web-served layer, casting the Mexico drawing into Pseudo-Mercator coordinate system. We begin the process using only two coordinate points and then we do a preview to see where accuracy of the proposed georeferencing result should be improved by adding more control points. We add more control points and then georeference the Mexico drawing with good accuracy.
Example: Import AutoCAD DWG and Georeference - Neither AutoCAD DXF nor AutoCAD DWG format provide coordinate system information. This example shows a typical case where documentation provided on the web site from which we have downloaded a DWG allows us to quickly and simply georeference the imported drawing.
Example: Import AutoCAD DXF and Georeference - Neither AutoCAD DXF nor AutoCAD DWG format provide coordinate system information. This example shows a typical case where we import a DXF using an unknown coordinate system, but based on a lucky guess we accurately georeference the imported drawing.