Georegistering an Image to a Drawing

Georegistering an image to a drawing is one of the most frequent tasks in GIS involving images. It's easy in Manifold:

 

Georegistering an Image to a Drawing

 

1. Open the image to be georegistered. Place as many control points as possible in the image at locations that may be readily identified in the reference drawing.

2. Click open the reference drawing to which the image is to be registered.

3. Place control points in the drawing at locations corresponding to those used for control points in the image.

4. Click on the image to make it the active window and choose Register in the Control Points pane. Manifold will present a dialog asking which component to use as the reference component. The reference drawing used in steps 2 and 3 above will be listed in the list box of available reference components.

5. Chose the new drawing for use as the reference. Manifold will re-project the image to match the control points placed in the drawing.

 

See the Georegistration topic for additional details on how to use control points to georegister images and drawings.

 

For brevity, this topic and other georegistration topics use images as examples. However, the same procedures apply when georegistering drawings or surfaces .

 

Tech Tip

 

Before georegistering an image to a drawing, if the image is in Orthographic projection (the default for non-georegistered images), take a moment to re-project the drawing into Orthographic projection centered on the approximate central latitude and longitude of the drawing.

 

Images that are imported from non-geographic formats will import using the default Orthographic projection. In most cases, such images are overhead views photographed from aircraft or satellites. Their natural appearance, therefore, is already effectively the same as their appearance in Orthographic projection.

 

Drawings, on the other hand, are quite often imported from geographically aware formats and so will usually appear within some projected form. Due to the difficult of saving projection information in simple GIS formats like .shp, many drawings that are published on Internet are provided in unprojected Latitude / Longitude form. Such drawings may appear distorted as compared to a direct, Orthographic, overhead view, especially in higher latitudes.

 

If the distortion is great enough, the visual difference between the image and the drawing may make it more difficult to pick out features in common. By re-projecting the drawing into Orthographic projection we can given the drawing a visual appearance similar to the image. This will make it easier to pick out features that are common to both the drawing and the image.

 

See Also

 

Georegister a Scanned Paper Map