3D GIS and GeoEye-1 GeoStereo Imagery

The notion of "3D GIS" has been gaining momentum in the geospatial industry for a few years now.  Witness the recent seminar conducted by the Britsh Columbia URISA chapter: "The New Dimension in GIS - 3D Analysis".  If the topic interests you, abstracts and many of the full presentatiosns can be downloaded from the site.  A look at the topics shows an examination of digital cities, 3D models, BIM, LIDAR, digital orthophotos orthophotos and more.  The industry has been abuzz with the integration of GIS, photogrammetry, and remote sensing for some time now, but only recently have the data products and tools have matured to the point of making integrated 3D GIS applications a reality.

Satellite imagery providers that have stereo collection capabilities are a good example of the drive to generate 3D data products.  As I've commented previously, the lack of industry standards for photogrammetric metadata poses a challenge to offering stereo products - but this is changing with data vendors pushing stereo products forward and efforts at the OGC-level to drive standards. An interesting item from Matt Ball's summary of the recent ASPRS conference in Baltimore was the keynote presentation from John R.G. Townshend, "calling for the standardization of imagery metadata".

GeoEye packages their satellite imagery products in a few different categories: Geo, GeoProfessional, and GeoStereo.  As stated on the GeoStereo product page, "the RPC camera model supports block adjustment, three-dimensional stereo extraction, DEM generation, ortho-rectification, and other photogrammetric operations. "  

GeoEye-1 Stereo Imagery in LPS

The benefit of stereo imagery is the value-added geospatial information that can be derived from it.  The quote above relates three specific data products: digital orthophotos, terrain models, and 3D vector data (three-dimensional stereo extraction).  Digital orthophotos have become a standard component in base map data, and can be used for accuracy assessment (e.g. are the vector data layers complete and correct?), 2D vector digitizing and update, change detection, and a number of other applications.  Terrain data, which can be automatically generated, is a key component for orthophoto generation, and is useful for a wide variety of other applications as well. The other data product mentioned above is 3D vector data.  One of the major benefits of stereo imagery is the ability to measure objects in X, Y, and Z and collect 3D vector data.  Not only can the vector data be extracted in XYZ, but the objects can be accurately extruded down to the ground level.  This provides a 3D object that can then be attributed, textured, and then fed into a variety of applications.   

Since we recently received GeoEye-1 GeoStereo imagery for validation in LPS, I thought it would be worthwhile running through the workflow in LPS 9.3.1.  In the next post I will outline the workflow steps - with the right set of tools, developing the products outlined above is a very straightfword process!  

Mapping Standards Directory Update

I've added a few new sites to the mapping standards directory. The new additions include a mapping manual from Minnesota DOT, a presentation on accuracy standards for mapping projects in North Carolina (from the NC ASPRS chapter), and various mapping specs from the Nova Scotia Geomatics Centre. All three are in the "Provincial/State Level Standards" section.

In particular the Surveying and Mapping Manual from Minnesota DOT provides a wealth of information, and it is relatively recent (updated in 2007).

Mapping Standards: A Directory

A few months ago I wrote a post regarding mapping standards and highlighted a few links. Personally I find this a critical topic in the mapping industry due to the massive growth of available data. While the quantity of available data is growing daily, there are naturally questions regarding data quality and lineage. How many geospatial professionals know the true accuracy of their data?

The importance of accuracy depends on the particular use case geospatial data is developed for. For example, being several few meters off might be ok for a local urban planning department that only needs to know the relative position of buildings and roads but could result in costly errors for, say, a Department of Transportation that requires engineering-grade accuracy.

Since I wrote the last post I've had a hard time finding a single place where I can find information about mapping/accuracy standards. So, I thought it might be helpful to start a simple directory of relevant sites. Please feel free to check it out and let me know if you're aware of any other sites that belong on the list. I know I'm only scraping the surface, so additional state, national, or private specifications and standards additions would be appreciated.

For those interested in production-level mapping, be sure to check out the "GeoBC Crown Registry and Geographic Base" (that is a mouthful) standards and specifications page. It has a wealth of content, from digital camera specifications (e.g. down to the nuts and bolts of camera calibration specs) to aerial triangulation, DEM, orthophoto specs and more. They've done a great job of putting it together all on one cohesive site.

Mapping Accuracy

The focus of today’s post is the importance of mapping accuracy and how it relates to geospatial data. Personally I think accuracy is one of the most difficult and misunderstood aspects of our industry. How many people out there in the geospatial industry have used data (vectors, orthos, or other spatial data) where you have no definite information about the accuracy of the data? How often can people confidently state that their data conforms to an accuracy standard? Furthermore, how many people have detailed information on the lineage of their data? For example, if you have a “roads” vector layer – where did it come from? Was it collected from high-accuracy aerial photography (where you know the triangulation results) in a stereo feature extraction system? Or was it digitized in 2D from a scanned map of indeterminate origins? These are critical questions for applications that require accurate data for making business decisions. The importance of accuracy is also application-specific. For example, in the USA the DOT’s (Departments of Transportation) require high-accuracy vector mapping data. If a road is built incorrectly, it is extremely costly to correct. Conversely, for an application such as a tourist map of a downtown area, often the relative accuracy is the only important factor. The precise coordinates aren’t so important, as long as everything lines up correctly and the person reading the map understands where they need to go.

For high-accuracy geospatial projects, customers (the organization purchasing the data) specify the accuracy requirements. Right now there are several standards for terrain, orthophoto, and mapping data. The USGS National Geospatial Program Standards are a good example. Other standards such as Federal Geospatial Data Committee standards can be found on the ASPRS Standards page. For a detailed look at accuracy standards, check out the Idaho Geospatial Committee's document for review on Aerial Mapping and Orthophoto Standards. It discusses accuracy in terms of the end-to-end photogrammetric workflow, from planning through final product generation.

I would also like to highlight Fugro EarthData’s recent Spring 2008 newsletter. One of the pieces, “The Call for a New Lidar Accuracy Reporting Framework”, features a discussion by industry experts Lewis Graham (GeoCue Corporation) and Karen Schuckman (Penn State University). This is a good read and I would recommend it for anyone interested in the topic of terrain accuracy standards. One of the key points is that many customers still define their project requirements in the form of contours: 2D cartographic representations of 3D data. Other topics explore horizontal accuracy, accuracy reporting standards, spatial variability of error, lidar processing errors, and more.