Jumat, 16 Oktober 2009

Thoughts on Google Building Maker and 3D Building Extraction

Earlier this week Google introduced the Google Building Maker, which it bills as a simple tool for creating buildings for Google Earth. I gave it a whirl earlier today and while it is a relatively simple toolset, the direction is impressive and has some broad-reaching implications for the future.

The Concept
The general concept is fairly straightforward: using nothing but a browser, you can create a digital 3D representation of building structures using a very basic set of tools. Target buildings are located from a top-down view, and then buildings can be digitized from a series of oblique photos. Several oblique photos can be used to ensure your measurements are accurate from various angles. When you're finished digitizing your target building, you can save it to the Google 3D Warehouse. Upon saving, textures from the various photos are automatically applied to the model. Once the model is uploaded to the 3D Warehouse, you may download it as a KMZ or Collada file.

The Workflow
1) The first step is to launch the Google Building Maker.

2) Once the Building Maker is launched, you have to select a city to extract a model from. At present there are a few dozen cities in the USA, Canada, Mexico, Europe and Japan available. Why can't you extract buildings from your hometown? Most likely because the entire system relies on oblique aerial (not satellite) photography for making 3D measurements. The reason more cities aren't available is because oblique aerial photography is not cheap to acquire: so it makes sense that the currently available cities are clustered in the more prosperous regions of the world. Think hyperlocal advertising...

3) Once you've chosen a city, you are provided with the ability to zoom into a location until you can see a placemark. Once you're at the right zoom level, you can select/drag/drop the placemark to choose the building you wish to model. One interesting aspect of this process is that, in the initial view, you are provided with a color coded graphic overlay of the particular city you want to create a model in. The blue area, typically in the urban core, shows where buildings already exist. The white area shows the areas where Google doesn't have 3D buildings but does have all the ingredients (read: oblique photography) to create them.

Legend: Blue = Buildings Already Exist, White: No Buildings

Selecting an individual building

4) After you have dropped a placemark on a building, hit the "Start Building" button on the left. This will switch your perspective from a top-down imagery view to an oblique perspective view. You'll also notice a series of modeling tools on the top right. These include add box, add gable, and add vertical freeform block. There is also a tool for toggling the snapping of points and lines, along with a series of tools for where to place the new block (e.g. above selected, below selected, inline with selected, and unconstrained height). The tools are very rudimentary. For example, it isn't possible to model curves. However, I believe the idea for now is to collect the basic building structure. If it is an easy rectangular building then no further modeling is required, and if it is a complex structure you have the option to "refine your building" in Google SketchUp after hitting the save button. This isn't a particularly slick workflow, but it is fantastic step forward for users without access to photogrammetric tools or other methods for making measurement from photographs.

Perspective View Prior to Building Extraction

Extracted Building

5) Once you've saved your model to the Google 3D Warehouse, you may download it as a KMZ or Collada file. This is a win-win scenario that provides both you and Google with access to your model.

Extracted building in the Google 3D Warehouse

Photo-textured building displayed in Google Earth

The Implications: What Does This Mean???

Personally I think there are a lot of implications for this technology on a number of levels:
  • Photogrammetry Software Vendors: can Building Maker replace proprietary COTS software for 3D feature extraction, such as solutions offered by ERDAS, BAE, and Intergraph (among many others)? In the short-term, no. The current Building Maker tools are simplistic and just scrape the surface in terms of functionality (e.g. no curves, no parallel lines, no attribution, etc). In the long term: Google is certainly setting the stage for a consumer-level system that may one day provide a robust system for 3D urban modeling. In that sense the Building Maker is a very disruptive move by Google.
  • Crowdsourcing: An interesting aspect of the system is that Google denotes the areas they already have buildings for during the selection process. The implicit message for users is: collect buildings that we don't already have (although in fairness there are no restrictions on collecting existing buildings - but why would you?). The other item of note here is that the areas that have oblique coverage that do NOT have buildings already tend to be suburban areas outside the core that consist of low-rise buildings. I can't help but think that this is a clever idea by Google to acquire buildings for free in these areas rather than partner with a professional services company to do the job. But to give Google due credit, they provide users with access to their models. This means that, as a user, I now can use Building Maker to create as many 3D models as I want and then keep the output. And furthermore, I can do this without buying stereo imagery and the software required to perform stereo feature extraction - which can be a significant sum even when considering a small area. As an individual consumer, I now have access to a measurement toolset that was previously only available to professional businesses that had made the requisite investments in both the data and software packages...
  • Is there a partnership between Google and an oblique vendor? Considering that Pictometry is the leading oblique vendor, I can't help but wonder if there is a partnership afoot. One thing to note here is that the oblique imagery is "Copyright 2009 Google".
  • Can this lead to "browser-based photogrammetry"? In recent years I've been a proponent of developing systems that hide the photogrammetry and offer easy-to-use tools to enable 3D geoinformation solutions. I find it quite compelling that this is what Google has come to the plate with: a solution that anyone can use (consumer grade) that makes measurement from aerial photography very easy, and then provides value-added capabilities such as photo-texturing. While 3D feature extraction is only one aspect of photogrammetry, I believe it is a sign of things to come that a giant such as Google has already come to market with a functional solution that many vendors have only been thinking of...
  • 3D measurements from mono imagery were commercialized initially (to my knowledge) by Geotango, which was subsequently acquired by Microsoft. This highlights the nascent competition between Google and Microsoft in this space.
  • As mentioned in the Google Earth Blog, the big limitation is the fact that you have to choose from a list of available cities. One can only wonder what this will do for the oblique airborne photography market...
At any rate, kudos to Google for once again changing the game!


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