Friday, August 29, 2008

Historical Aerial Photography at the Serge A. Sauer Map Library

For today's post I'd like to highlight the Serge A. Sauer Map Library. Housed at the University of Western Ontario in Canada, the Map Library has large repository of maps in both hardcopy and digital form. The library also has a large stock of aerial photography, and recently made an air photo project flown in 1922 available online. The project page allows you to view and download the photographs via a mosaic or through a Google Maps interface. From the drop-down menu on the Google page, it looks like aerial sets from other years are coming soon.

The steps used to produce the mosaic are also available. While the process was very "manual" (rotating and scaling the images until the fit a basemap), the end result is a good looking historical mosaic!

Tuesday, August 19, 2008

What's New in LPS 9.3 Webinar

You should be seeing a press release on shortly, but I wanted to highlight the fact that we are planning a webinar on the new release next week. While we just released LPS 9.2 earlier this year, the LPS 9.3 release is now in beta and we are looking forward to getting it on the market soon.

I highlighted one of the new features, KML Export from the LPS Block File, in a previous post. The webinar will proceed to highlight the new enhancements and solutions, as well as a live demonstration of certain capabilities.

Anyways, you can check for more details including registration for the free webinar on the ERDAS site in the next 24 hours.

Friday, August 15, 2008

Sensor Spotlight: Thailand Earth Observation System (THEOS)

You might have noticed that last year we released a PR regarding support for the THEOS sensor model in both LPS and ERDAS IMAGINE, which was due to launch last week. Unfortunately the satellite launch has been postponed, but we're looking forward to a successful launch once the new date has been set.

A THEOS engineer, Suwan Vongvivatanakij, put together an excellent overview presentation for the CEOS Working Group on Information Systems and Services (WGISS) for their meeting last February. I haven't seen a lot of detailed information about the satellite on the web and thus far this is the most comprehensive info I've seen.

The satellite has panchromatic and multispectral modes, with a 2 meter resolution at nadir for panchromatic and 15 meters for the multispectral mode. For mapping, stereo applications will be supported since there are three (forward, nadir, reverse) look angles.

If you hail from Thailand (or can read Thai) you can see the THEOS program homepage here:

Wednesday, August 13, 2008

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.

Monday, August 11, 2008

DigitalGlobe on NBC: A Closer Look at 3D Olympics

I've seen a couple of posts regarding DigitalGlobe's Bejing Oympic Games coverage. In my opinion this is a great consumer-grade marriage of geospatial technology and mainstream media. On the DG homepage "DigitalGlobe on NBC" is prominently displayed, which takes you to, their site with EAgis Technologies (a joint effort between DG, EAgis, and NBC).

The posts above comment on the technological underpinnings on the 3D scenes offered on the new site. One common theme is how a combination of different technologies (photogrammetry, 3D modeling, satellite imagery, 3D visualization) can be used together to provide a powerful and immersive viewing experience.

The site allows visitors to download 3D PDFs, a KMZ and perspective views of various Olympic sites. 3D PDFs have been around for awhile, but this is the first time I've had a chance to examine one: very cool, although not the same experience as a KML file in a virtual world. Compare for yourself below:

KML in Google Earth:

Aside from the availability of 3D example data, the site also provides some insight into the creation of the dataset. The "How Can This Be Possible?" heading expands to provide a high-level introduction to the technology and workflow. The workflow is divided up into four parts with a graphic associated with each one: the "3D wireframe" generation, imagery capture, feature extraction and extrusion, and fully textured 3D model generation.

"3D Wireframe" Generation

The site mentions that the wireframe represents the earth's terrain, and that it was derived from two DG satellite images. Sounds like classical photogrammetry! Two images associated with sensor model can be viewed in stereo to extract (measure) 3D positions (e.g. points with an accurate XYZ location). For high-accuracy applications relying on the satellite sensor model may not be enough, and there would be a need to collect and measure ground control points and then run through the triangulation process. However, once that is done there are numerous applications that may be used for terrain extraction.

The screen capture of the wireframe is actually a Triangulated Irregular Network (TIN), which when compared to raster DEMs is a more efficient means of modeling terrain. These can be automatically correlated using point matching algorithms or manually compiled by hand - which can be a very time-consuming process.

Why is the TIN important? The terrain represents a fundamental part of an immersive 3D scene. If it isn't accurate then the scene will not look realistic... In inaccurate terrain model could also cause problems in the image processing (orthorectification) part of the workflow.

It is also important to note that terrain can come from a number of sources: manual compilation, automatic correlation, LIDAR, IFSAR, and other sources.

Imagery Capture

This screen capture shows imagery draped over the terrain. The imagery would have come from QuickBird or WorldView-1 satellites. For a good-looking scene high-resolution satellite imagery or aerial photography is important. Sometimes satellite imagery is useful, but often aerial photography is the best solution. Why? If imagery is captured from a sensor mounted on a plane, the data acquisition organization has full control over the scale/resolution of the photography. Flying low equals higher resolution...

Another important note is that the terrain model discussed in the previous step would likely be used to orthorectify the image. This will result in a geometrically accurate orthophoto with real-world coordinates. The accuracy of the terrain is important: if there are large errors the 3D features discussed in the next step may not appear in the correct position if they were extracted in a stereo feature extraction system (building footprints digitized off the orthos and then extruded would be ok though).

Feature Extraction and Extrusion

The text for this segment talks about "special tools" being used to determine "footprints" of buildings and then extruding them. This might work for some rectangular buildings with flat roofs, but it is clear that all the download-able content on the site was not derived from automatic extrusion. There are a couple of ways to generate 3D buildings. The quick an dirty way (extrusion) involves digitizing the building footprints in 2D from a digital orthophoto. Then you need to tag the building polygon with an attribute to represent height. This is a fairly straightforward procedure if a digital surface model (DSM) of the area is available. The drawback of extrusion is that, although quick, it may not be accurate. Extrusion assigns one elevation value for the entire building (roof) area, so buildings with pitched or complex roof structures will not be modeled accurately.

Photogrammetric feature extraction can model buildings with greater detail, since specific building detail can be modeled in stereo by viewing and measuring buildings in 3D. However, photogrammetric feature extraction is performed from a "top-down" perspective, so features like balconies may be difficult to model. This is where CAD or CAD-like 3D modeling packages and ground-based photography can help. One workflow for 3D city construction is to photogrammetrically extract the buildings and then import them into a CAD package to add more detail to the models. Ground photos can also provide photo-realistic image texture, as can aerial photography, but capturing all four sides of a building can be difficult without planning the acquisition flight with a very high degree of overlap - which can add to the project cost (more fuel, more data to process). In addition, aerial photography may not be able to capture street-level image texture or areas with dense skyscrapers.

At any rate, there are many ways to go about generating the 3D buildings - it all depends on the level of detail required and the project budget...

Textured 3D Model Generation

As I mentioned above, texture can be applied to buildings from both ground and aerial photography. There's a number of tools that can be used to texture the buildings, here is an example video of how this can be done in SketchUp. There's a number of 3D modeling applications out there to do this sort of work. Again, production costs rise an accordance with the level of detail applied to a building. A "perfect" building cannot be easily automated and can be laborious to produce in sophisticated packages such as Autodesk's 3ds Max.

Looking at the Beijing Institute of Technology model it is clear that a lot of effort went into building it. Not only does the texture look great, but there is a lot of 3D modeling that has been done in a professional 3D modeling system. The rounded rooftop would be very difficult to model in a photogrammetric feature extraction system, and the model contains detail of the roof overhangs - which would likely come from the use of ground photography.

At any rate it is nice to see this technology getting some mainstream media coverage. Photogrammetry and 3D mapping have been around for a long time, but the mass-market popularity of visualization packages such as Google Earth is exposing this technology to a much broader audience.

Wednesday, August 6, 2008

LPS 9.3 Preview: KML Export

We're getting late in the release cycle for the upcoming LPS 9.3 release (the beta testing phase has now started!) so I thought I'd start previewing some of the new functionality we're releasing.

An increasing number of geospatial applications are supporting KML (although the word "support" can mean a lot of things), so mentioning that we'll be able to export the LPS Block File as a KML file isn't earth-shattering news. However, KML in the context of photogrammetric applications is relatively new and there are some interesting implications.

First I'll show how the exporter works and then get into what some of the uses are. Here's a screen capture of a small photogrammetric project in the LPS Project Manager, in area of Waldkirch, Switzerland.As you can see it is a relatively "complete" project. There are triangulated images, GCPs and Tie Points, some DTMs, and orthophotos. From the Project Manager, we have a new drop down entry in the "Tools" section called "Export to KML". Click on this and the following dialog appears.The dialog allows you to choose which elements of the photogrammetric project (Block File) you would like to export. Check the various boxes and then you can hit the "Export" button to generate the KML file.

For this dataset I've uploaded the output KML file here. Feel free to download it and check it out. Note that the various photogrammetric data elements (e.g. Ground Control Points) can be turned on and off. Here is a screen capture of the file in Google Earth.
So this brings us to the question, why is this relevant? The first thing that comes to mind is project tracking and status reporting. Photogrammetric/mapping projects are increasingly completed in disparate geographic areas. This can make project tracking a challenge. While there's a mixed-bag of current approaches to project tracking, a KML file can provide a relatively compact (especially if you leave out the tie points) and visual representation of what parts of the project are complete. For example, an organization with an office in the USA that is working with a partner in another part of the world could request daily updates of status for a large digital ortho project. By looking at the "orthos" layer, the project coordinator could not only see how many are complete (like they may currently do with MS Excel or other spreadsheet apps) but also see a visual of the completed project areas. Thus, they could see if the "challenging" parts of the project had been tackled yet (e.g. rugged terrain or urban areas) and manage accordingly.

I'll talk about this a bit more in future posts, as well as hightlight some of the other solutions we've been working on this year. We're certainly looking forward to getting the new release out!