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.

The Role of Seams in High Resolution Image Mosaics

When discussing true orthophoto generation I made reference to the image mosaicking process. I thought I would touch on that more today, with an emphasis on high resolution imagery. One of the main challenges in mosaic production is ensuring the mosaic is seamless. That is, one cannot easily discern where the edges of the input images are. This can be challenging for a number of reasons. One of the most difficult aspects involves the input image geometry. Because the input images have different perspective centers, the geometry of surface objects will vary between images. For example, a tall building in the center of a frame image may not exhibit any building lean, but the same building in the next image will show noticeable lean. So the big challenge in the mosaic process is ensuring the seams between input images conceal any mismatches. While seams between the images can be automatically generated, a quality control check must be performed to ensure there are no issues. Seams usually need to be manually edited if there are any problems.

Here's an example: the image below shows a multi-story building with a seam cutting right through it. Because the angle of building lean is different in each images, it looks like a mess.

In this example, the seam has been edited so that it shifts north of the building. This is ok, but it also reveals that there is a lot of building lean in the image portions chosen for inclusion in the mosaic.

This example shows the same building with the seam edited the other way. Instead of diverting north of the building, I've moved it to the other side. You can see that this provides a better top-down perspective on the building, which will generally make for a better output mosaic.

Another typical problem area: bridge decks. The image below shows a seam cutting through a freeway overpass. It is easy to see that the edges are misaligned.

Below, the seam is edited to run parallel with the bridge instead of cutting through it.

Note that accuracy issues in the terrain model used to create the input orthophotos, such as not having accurate enough terrain or the existence of errors in the terrain, can also introduce "mismatches" between images. In the bridge example above I used a DEM where I modelled the terrain with reasonable accuracy (performing terrain editing in stereo), but I stopped short of modeling the bridge decks. This means that the image area of the ground is accurate, but there is some offset for the bridge. While the seam editing technique hides the error and creates a visually-appealing result, the fact remains that the ortho may be considered flawed because the seams in the mosaic simply mask the error - they do not eliminate it.

Historical Maps at the World Digital Library

The recently-opened World Digital Library is another great resource for historical maps (see here for another, and also see the recent post at VerySpatial).

The main page allows you to filter results by date range and region and then you can narrow your search with a number of options, one of them being "maps". The maps can be viewed in flash, with zoom control, and it is also possible to download a TIF image.

The map below is a 1507 world map that was first to depict the Western hemisphere with the Pacific Ocean as a distinct ocean (click on the image below to see the details). Check out the site if you're interested - looks like they have over 300 maps already online. Details about the project are available here, and it an associated Slashdot discussion here.

Journal of Maps: Research-Based Maps Online

The Journal of Maps is an electronic publication dedicated to the publication of research-based maps.  Although a login is required, registration is completely free and one you are logged in your can access a number of research papers.

The journal features a worldKit-based interface that features research paper map extents displayed over a global map.  The site also provides the abiilty to view the map locations in Google Maps, displayed below (or see here).  

View Larger Map

It is great to see a forum emerge for interactively browsing research papers by geographic areas as opposed to the more traditional approach of searching based on subject.  It should be interesting to see how the journal develops!

Photogrammetry Meets Kite Aerial Photography (KAP)

Kite Aerial Photography, as the name suggests, involves rigging a camera up to a kite system and then using it to take aerial photographs. After seeing my previous post on photogrammetry with a camera attached to a helium-balloon, Dr. Mike Smith at Kingston University contacted me about research he has been conducting in the realm of KAP and photogrammetry. Along with Drs. Chandler and Rose, he recently published a paper in Earth Surface Processes and Landforms entitled "High spatial resolution data acquisition for the geosciences: kite aerial photography".

The paper is relevant for the mapping industry because it provides an overview of the aerial acquisition process, the photogrammetric processing, and then an accuracy assessment of the results. I'll start with the results: their methodology enabled the production of stereo pairs, digital elevation models, and stereo imagery. Furthermore, the stereo imagery was triangulated with an accuracy of roughly 10mm in planform against surveyed ground control points.


The methodology involved using a 6 megapixel Nikon D70 camera and collecting aerial photography at altitudes of up to 200 meters over three test sites in the UK. GCP targets and XYZ samplings for topographic modeling were measured with Leica Geosystems TPS1200 and TCA 1105 Total Stations.

All the photogrammetric processing was performed in LPS. This involved setting up an LPS Blockfile (a project file), adding the images, and subsequently running through the aerial triangulation process in LPS Core in order to produce stereo pairs. With oriented images, the LPS Automatic Terrain Extraction module could be used to generate a digital elevation model. Next, the oriented images along with the digital terrain could be used to produce digital orthophotos. The paper describes the process in a high level of detail, as well as an excellent evaluation and discussion of the results.

Here is an image of an orthophoto superimposed with terrain points (red = automatically extracted, blue = measured via total station):

And here is a perspective view of an orthophoto draped over a corresponding digital elevation model, with contours:
In my opinion it is a great looking product considering it was generated with a 6 megapixel SLR camera flown from a kite!!

So why is this relevant for the mapping business?

The study illustrates a great low-cost approach to localized (as opposed to wide area) mapping, which means it may very well be a viable option for applications ranging from mapping cultural heritage sites to localized studies on soil erosion and other environmental and natural resource mapping projects. It is significant because it represents a significant cost saving over the traditional helicopter-based approach. If I had any talent for flying big kites I'd give it a whirl, but for now I'll leave it to he pro's...

Europeana: Historical Maps Online

I was browsing around Europeana, which made international news with its debut and subsequent crash in November, when I found that it is a great resource for archived historical maps. If you visit the site and search for, say, "map", you'll get all sorts of results. The "refine your search" tools on the left are good for filtering by country, provider, or other parameters. For instance, I filtered on Bibliotheque Nationale de France as the provider and found a great historical map of the British colonies in the USA and southwestern Ontario. Clicking on the "view in original context" will take you directly to the source, which in this case takes you to a full-screen viewing application when you double-click on the map.

The British Library, another "provider" search refinement option, has an impressive number of historical maps as well. They are also available in a nice flash viewer, such as this 1530 map of Ireland.

Oblique Imagery

From my perspective the market for oblique aerial photography has gone from a very niche application area and morphed into something altogether different. With the advent of organizations like Pictometry and applications of their photography such as the "Bird's Eye" view in Microsoft Virtual Earth, oblique imagery is entering a number of market spaces. Oblique aerial photography is not new though, however early attempts to commercialize the technology such as Kodak Citypix from several years back never really got off the ground.

I would be interested in thoughts on usage of oblique photography versus nadir "top-down" orthophotos. My view is that nadir photography is most appropriate for "measuring" objects within photos (GIS "backdrops", building areas, parcels, roads, etcetera), whereas oblique imagery is better for contextual information. So from a "mapping" perspective traditional top-down imagery may be more appropriate but for a navigation system my preference would be for oblique.

From an end-user/consumer perspective there is certainly a lot of value in oblique photography. One problem with nadir imagery is that it can be difficult to tell how tall buildings are, or gather any information about buildings (or anything other features with a "vertical" aspect). Oblique photography allows users to see the sides of buildings and other objects, which has a lot of appeal for a variety of applications.

The downside of oblique imagery is that, depending on the angle, objects in the foreground (e.g. highrises) can obstruct the view of anything behind them. They can also be difficult to integrate in a GIS, as most GIS apps feature a "top-down" perspective when you're looking at the data. For photogrammetric applications, it also isn't very practical to work with high oblique images in stereo.

Here's an exampe: the image below is a nadir view from Microsoft's Live Search Maps in Pacific Beach, San Diego. One can clearly see roads, all the buildings (from a top-down perspective), and the coast.


The image below is the same area with the "Bird's Eye" oblique perspective view. It immediately becomes apparent that there is a highrise along the coast, which obstructs the view and casts a shadow on several buildings behind it - useful to know if you're in the real-estate business. The bluffs along the ocean are also exposed.


And finally, here is another oblique aerial photo of the same area taken facing east. This is a closer-range and lower-altitude oblique shot than the images above, so a lot of building detail can be seen (e.g. one can determine the number of stories of the properties along the coast). This image also illustrates how the objects behind the highrise are obstructed - you'd need to take a look at the "top-down" nadir view to know what is there.

Click on the thumbnail above for higher resolution

Incidentally, the above photo is from the California Coastline Records Project. If you haven't heard of it, a visit to the site is highly recommended. The project has coastal oblique coverage of nearly the entire California coastline, taken from a helicopter approximately 500 feet offshore. The project has essentially created an online repository documenting the status (and damage to) the coastline. In celebrity news, the project was unsuccessfully sued by Barbara Streisand, who took issue with online photographs of her Malibu compound...

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.