3D/Stereoscopic Video Samples

I haven't thought about 3D video much before, but a newsletter sent out from Planar highlighted a nice 3D video they put together. You can find out how to view it yourself and download samples on the Planar3D blog.

One interesting thing about the Stereoscopic Player from www.3dtv.at is that you can specify and left and right video. This makes stereo display ideal for a Planar monitor, or if you have a pair of red-cyan glasses you can view them on an LCD display (e.g. a laptop display).

Downloading ASTER Data and More...

With all the recent media attention, it seems like it is best to wait a bit before trying to download any of the data. The Japanese site (ERSDAC) published a warning earlier today that downloads may timeout, and I had a challenging time even getting the USGS site to load:

I have mentioned this before, but here is a paper on hydrology/glacier mapping in the Tien Shan mountain range using both ASTER and SRTM elevation data. One of the benefits of ASTER and other satellite sensors is that they are very applicable to remote area mapping operations.

So while you're waiting for ASTER traffic to subside, why not check out the ASTER User Handbook? It contains a wealth of background information on the sensor, data products, processing, applications, and FAQs. Here it is:

USGS: aster user guide v2

2009 NAIP Status Update

As mentioned on the NSGIC News Blog, the National Agriculture Imagery Program (NAIP) for 2009 will cover roughly two-thirds of the USA. This is quite an achievement for the program and will result in an excellent resource for geospatial practitioners as well as the broader public.

A status update from yesterday indicates that flight operations are already well underway.

The 2009 program contractors include a group of commercial mapping firms that are all well-known in the North American mapping industry: 3001, Aerial Services, the North West Group, Photo Science, Sanborn and Surdex. It is interesting to note that the cameras used will be a mix of large-format frame and pushbroom sensors. 3001 has both a Leica Geosystems ADS40 (pushbroom) as well as an Intergraph DMC (frame), and I'm not sure which will be used for NAIP acquisition. Aerial Services and the North West Group operate Leica ADS sensors. Photo Science and Surdex operate DMCs while Sanborn operates a Microsoft Ultra Cam (frame). The photogrammetric processing workflows for frame and pushbroom sensors are quite different, with pushbroom sensors capturing long strips of imagery in a "pixel carpet" versus the traditional frame approach. However, it is good to see a mix of technology in use.

Here is a map of the contractor areas:

Note that further maps and status updates are available from the APFO (Aerial Photography Field Office) home page.

Terrain Point Cloud Extraction from High Resolution Optical Images

If you've been to ERDAS Labs then you probably know that we are developing a new automatic terrain extraction solution. One of the unique things about the project is that it has given us the opportunity to think carefully about how we persist terrain data, and last week I had a chance to discuss this at the ISPRS Workshop in Hannover, Germany. I don't have a recording of the presentation, but here are some of the details:

1) Digital imagery is achieving increasingly high resolutions. We are now at a stage where airborne sensors can achieve higher than 5 centimeter pixel resolution.

5cm Resolution ADS80 Imagery

2) Many softcopy auto-correlation systems (XYZ terrain point matching system) were initially developed upwards of a decade ago, and were not designed to take advantage of high resolution sensors. Our own LPS ATE module was originally released in 2001 as "OrthoBase Pro" (timeline here). One of the features of some more modern systems is the ability to attempt correlation on every pixel - which can yield a very large volume of data.

117 Million Auto-Correlated Terrain Points

Detailed View: Terrain Points on Individual Boats

3) TINs and Grids, the traditional formats for persisting terrain data in softcopy photogrammetry and GIS, may not be optimal for high resolution terrain data: hundreds of millions of points at a high density. Both have pro's and cons, which Gene Roe has outlined here. Grids can be redundant (particularly for flat regions) and while TINs are very flexible in this regard, they have no standard format. Each vendor has their own implementation, making data translation and transportability a challenge - not to mention long-term storage.

4) The LAS format, while designed for use with LIDAR sensors, may be a viable alternative to TINs and Grids for autocorrelated terrain data. Why? There are a few different reasons:

• LAS is an ASPRS-administered standard and has a high adoption rate among geospatial software vendors.
• The LAS 1.2 specification supports attribution, for example the ability to encode an RGB value for each terrain point. While it isn't commonly used within the LIDAR community, it is very useful for auto-correlated terrain. This allows RGB-encoded terrain to be used for applications such as visualization. Capabilities such as this are not possible with the traditional TIN/Grid approach.
• When correlating on every image pixel, terrain data can be very dense. A compelling research area involves applying LIDAR classification and filtering techniques to autocorrelated terrain data.
  

Point Cloud with Color Attributes (CIR, Red, Green: ADS80 Imagery)

Detailed View: Point Cloud with Color Attributes (CIR, Red, Green: ADS80 Imagery)

The images above show color attribute encoding for an LAS 1.2 point cloud that was processed from stereo ADS80 imagery. The bottom image is a zoomed in perspective view showing a lot of detail: solar panels on the roof, cars, and a feeling of depth in the empty pool. These images show the point cloud rendered as a TIN within the FugroViewer. As you can see, the terrain representation is quite different from a traditional TIN or grid.

LPS eATE at ERDAS Labs

You may have seen the press release regarding the new ERDAS Labs website. One area I would like to highlight is the LPS eATE Preview section. This features a movie and a blog post (New Algorithm for Automatic Terrain Extraction) by Dr. Neil Woodhouse, who has been involved with our new terrain project since the start. As he suggests in the post, we chose to develop a completely new solution rather than incrementally improving the current LPS ATE product - which was originally released as Orthobase Pro back in 2001.

Both the movie and the article feature Neil working with and discussing auto-correlated terrain persisted in the LAS format, which is more commonly associated with LIDAR data but also makes a great deal of sense for dense (high resolution) terrain data as well. Note that the software used to present the data Neil discusses in the movie is the FugroViewer, which I discussed here. One of the nice aspects of the FugroViewer is that is shows RGB-encoding for both the point cloud and a derived TIN - which is great for visualization of the terrain surface.

One other thing to note is that eATE is still under development, but we are looking forward to releasing the initial version!

Exploring Stereo 3D Feature Extraction (Part 2)

While the previous post introduced the concept of 3D stereo feature extraction, this post will focus more on specific tools for 3D vector capture.

For urban 3D modeling, manual stereo feature extraction typically involves collecting rooftops (and sometimes even more detailed structures such as rooftop mechanical features) as 3D polygon features. To create solid 3D models, an extra step is taken to extrude the feature down to the ground. There are typically numerous methods for doing this. In PRO600, an ERDAS application that runs in both the Bentley Microstation and PowerMap environments, there are three options for building extrusion via the “Create Building” operation:

• Manually measure the ground height.
• Specify a fixed object height.
• Extend the feature down to the surface of a digital elevation model.

If you have a DEM available, clearly this is the least time-consuming option - because you can extrude a large number of buildings all at the same time. There are also a number of options to consider when performing the extrusion: see below for Object Creation options (click on the image to enlarge):

Create Building and Object Creation Preferences in PRO600

To demonstrate extrusion and object creation, here is a screen capture of a set of extracted building features. These have all been extruded with the aforementioned “Create Building” operation.

Extracted 3D Building Vectors Displayed in Bentley PowerMap

Here is the same feature dataset with an orthophoto backdrop. Notice how the building polygons fall around the base of the building (the true location) and not the tops of the buildings. This is one of the advantages over heads-up digitizing directly from orthophotos. If the building has any lean at all, then tracing rooftop vectors off the ortho will produce building polygons in the wrong location.

Building Vectors and ECW Orthophoto Displayed in Bentley PowerMap

Switching to an isometric view and altering the display mode, you can see the buildings rendered from a perspective view.

Perspective View of 3D Building Vectors in Bentley PowerMap

While extruding features is one thing, the process of capturing them is another. PRO600 features an extensible library catalog containing feature definitions. While a default catalog comes with the software, it can be completely modified or replaced if necessary. Double-clicking on a feature in the catalog shows the feature attributes (color, description, style, etc.) which can then be edited and saved. Collected features can also be selected an modified on an individual basis. For example, you may have a selection set of buildings that you would like to highlight with a different line thickness and color to make them stand out from the rest of the building vectors in the dataset.

PRO600 Library Catalog and Shape Definitions

While the "Building" feature above triggers off the "Collect Squared" Microstation/PowerMap command, it is also possible to switch into arc-collection mode mid-feature to model any curving or circular lines. An increasing number of building structures feature curving corners instead of sharp edges, making tools like this a necessity.

Modeling complex feature can take time, so snapping is also important. PRO600 has a few different snapping options, including 2D, 3D, and a 2D/3D hybrid - where the tool switches between 2D and 3D based on a user-defined tolerance. Here is a look at the snapping preferences, which also show optional modifications such as the ability to cut a vertex or add a new vertex (to the feature being snapped to).

PRO600 Snapping Preferences

Aside from building polygon features, there are also specific tools available for mapping linear features such as roads. For example, a parallel line tool is available to reduce the time required to digitize both sides of a road or freeway feature. Since photogrammetric mapping has been widely used in the engineering community (e.g. State-level Departments of Transportation in the USA) a number of tools have emerged that are particular to high-accuracy, high-throughput mapping applications. Fortunately, these tools also lend themselves to a broad number of other applications, including visualization, 3D city modeling, urban/environmental planning, and much more.

Exploring Stereo 3D Feature Extraction (Part 1)

Manual operator-driven 2D and 3D feature extraction techniques have in use for many years. One of the early methods of getting data into a GIS was from 2D digitization. In addition to tablet digitizing systems, softcopy photogrammetry approaches to vector data have also been available for many years.

Remember this? Click the image for details

The photogrammetric approach, also known as stereoscopic feature extraction, is one step closer to the source of the data than GIS-based digitizing. Instead of compiling feature data from an orthophoto or another source of information, stereo extraction uses the original images along with the triangulation metadata. The triangulation metadata consists of exterior orientation parameters that are required for stereo pair generation. Exterior orientation data could also come from airborne GPS/IMU data – which may be necessary for mapping remote areas where collecting ground control points is not an option.

Stereo feature extraction is inherently 3D. The vector data are measured in X, Y, and Z by manipulating a floating cursor while viewing a stereo pair of left and right images. As a result, the point, line, and polygon feature data all have Z values associated with each vertex. Because GIS developed in a 2D paradigm, many early stereo feature extraction packages were coupled with CAD environments as a platform. Basically a stereo viewer would be added for stereo image viewing and 3D measurement, and the feature data would render in the application's native “viewer”. In more recent times applications have been developed for GIS packages in addition to CAD environments, as well as a number of native applications that do not require platform technology.

Stereo Feature Extraction in PRO600

So why is this important? Data used for GIS analysis needs to come from somewhere. While there are a number of methods used for generating vector data, the demand for 3D vector data appears to be on the rise. One area of current discussion is the format and environment for generating and persisting 3D vectors. Currently the end application tends to determine the format, but this can be challenging for people trying to create one-size-fits-all data products (e.g. if I want to create a textured 3D city model, what format should I use without being locked into one system?). In this respect the development of CityGML is intriguing, as the geometric properties are but one aspect of urban information modeling and are viewed as an inter-related component of a much broader system. But persistence models aside, tools are still required for the original content generation.

More on specific 3D feature extraction tools tomorrow...