3D Site Modeling ni Context

Georeferencing Images in Sketchup

This page discusses a couple of ways of georeferencing groundplan images in Sketchup. The basic idea is that a groundplan for a project may originate in any number of tools. The original geometry of the existing groundplan may originate as an areial photograph which is then used as an underlay for a pencil sketch of a proposed re-working of streets and open spaces in the greater context of a site. You may have a site plan in an Illustrator document or from a PDF. In any case, it is very useful to move such information into sketchup to use as a Reference Image for fleshing out the plan in 3d. Groundplan images are also useful for draping on terrain models to provide a quich thematic texture that explains at a glance, the relationship between groundplan elements, terrain, built systems and vegetation.

Frames vs Pins

We will explore two fundamentally different ways of georeferencing groundplan images. The first employs the Get Location capablities of sketchup to acquire a couple of geo-located registration pins that are used to scale and rotate an image. This method is nice because it relies only on free web sources. The pins method wil probably be the method of choice for most users, although the georeferencing of the each image takes several steps. The second method uses the notion of a georeferenced referencing frame that has been created in GIS or in Google Earth. The frame method requires techniques that may be beyond the capabilities of some users, however, the use of frames makes it very easy to exchange revised images in and out.

Textures vs Reference Images

Regardless of whether you use pins or frames, there are two ways of using images in sketchup that all users should be familiar with. When importing an image in sketchup, you have the choice of Import as Image or Import as Texture. It would be better if the distiniction offered by the import dialog concerned Import as Reference Image since a texture is an image, too. What makes the Image option attractive is that Images in sketchup do not become invisible when one is editing inside the context of a group. Therefore reference images serve very well as a base-map over which you can trace buildings and blocks, etc that can be grouped and viewed in X-ray mode with the image visible underneath. Using an image as a Texture, on the other hand, allows the image to be projected onto irregular surfaces -- such as terrain models, orapplied to faces as tiled materials to create patterns like pavements or vegetation. Image textures, like other materials become ghosted and more or less invisible when they are outside of the context of whatever group or component is currently being edited.

The Georeferencing Pins Method

Using a Georeferencing Frame Created in Sketchup

This workflow allows you to get georeferenced images from Google Earth.

The Georeferenced Frame Method

This demonstration deals with the situation in which you have some detailed groundplan information in ArcMap that yopu would like to use as a georeferenced base in Sketchup.