Photogrammetry News: Photogrammetric Week 2009

It has been a busy summer and as a result I haven't had much time for keeping up to date with The Fiducial Mark. But with an inter-continental move from Belgium back to Canada wrapped up, there is a lot of news in the mapping business to comment on.


One major event that comes along every couple years is Photogrammetry Week in Stuttgart, Germany. This event, which was held a few weeks ago on September 7-11, is a great forum for learning about the latest developments in airborne sensors, software, and general industry trends. For those of us that didn't get a chance to make it over, the Institute for Photogrammetry at the Universität Stuttgart hosts a web-site containing the agenda, photos, and papers from the conference. The "Papers of the 52nd Photogrammetric Week" section contains a gold-mine of information, and a review of the articles provides a look at where things are at in the industry today.

Papers are divided into four sections:

Introduction: Presentation papers from the University of Stuttgart, Hexagon (Leica Geosystems and ERDAS), Intergraph, Vexcel Imaging (Microsoft), Trimble Geospatial, and IGI. These papers provide company overviews, organizations updates and a common focus on sensor updates (e.g. ADS80, UltraCamXp, etc).

Image-based Data Collection: these papers largely focus on airborne camera systems. One interesting paper is "Digital Airborne Camera Performance - the DGPF Test" by Michael Cramer. DGPF is the German Society of Photogrammetry, Remote Sensing, and Geoinformation. The paper discusses an ongoing project evaluating the strengths and weaknesses of various digital sensors, covering systems from Intergraph, Leica Geosystems, Jenaoptronik, Vexcel Imaging, IGI, Rolleimetric, and DLR Munich. The project involved data collection flights over a well-controlled test site near Stuttgart. In reading the paper, it becomes clear how difficult it is to perform precise apples-to-apples tests between systems - given how many factors can impact the performance of a system (e.g. weather). The paper focuses on geometric accuracy and provides detailed information on the studies conducted thus far. It will be interesting when results are available from the radiometry working group, because this is an area where there are a number of differences between the above sensor systems.

Other interesting papers in this section are "Oblique Aerial Photography: a Status Review", and "The Bright Future of High Resolution Satellite Remote Sensing - Will Aerial Photogrammetry Become Obsolete?" The oblique paper is a good reminder of how Pictometry has come to dominate this particular niche. While I don't believe aerial photogrammetry will become obsolete anytime soon, the second paper raises some great points on the development of satellite-based photogrammetry.

LiDAR: Airborne, Terrestrial and Mobile Applications: numerous papers on both hardware and processing developments for airborne and terrestrial LIDAR applications. The intriguing topic here is how mobile laser scanning is becoming increasingly relevant (Gene Roe adds insight on this topic as well here).

Value-Added Photogrammetry: articles providing a look at where current photogrammetric processing research is focused. The topics range from standards (CityGML), sensor to internet workflows (ERDAS is in a unique position of being the only company that can really offer a solution that starts with data capture and ends up with on-line data delivery and web services), digital image matching, cultural heritage, and more. Automated terrain extraction from stereo imagery is being pursued with renewed vigor, and it is good to see standards appear on the radar as well. Although I failed to see any developments on standards with regards to photogrammetric metadata, it will be great progress if CityGML gains momentum for one of photogrammetry's primary data products: 3D models.

Kudos to the conference organizers for sharing the conference materials - it is a valuable resource and greatly beneficial to the broader geospatial community as well. Sensor data and photogrammetric processing technology is the root of 3D geo-information, and it will only be a matter of time before these technologies embed themselves in an even broader array of applications.

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.

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...

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...

National Agriculture Imagery Program (NAIP) Best Practice Report

A couple of days ago I stumbled across a report put together by ITT for the USDA's APFO group outlining suggestions for improving NAIP image quality. If you're interested in the radiometric processing of aerial photography, this is a must-read. The document outlines image collection guidelines (e.g. optimal flying conditions), the assessment of imagery quality, and image processing recommendations. Some of the material (e.g. orthorectification) is relatively high-level, but the sections on radiometry are great. Also be sure to check out the end of the document, which features a set of screen captures depicting radiometric problems and solutions (pre and post-processing) for image noise, sharpness, clipping, contrast, saturation, and color channel registration.

One thing to note is that NAIP imagery is generally available to the public. Aside from the USDA/NRCS Geospatial Data Gateway, it is also accessible from a number of regional/state-level organizations. A great resource for free orthophotos, NAIP and otherwise, is the World Wind Central section on the topic.

For some practical advice see Jarlath O'Neil-Dunne's recent post (and particularly the video) on the methodology and benefits of using the Vermont 2008 NAIP imagery in a GIS.

Mapping Unexploded WWII Bombs in Germany

While visiting our German business partner, GEOSYSTEMS, in Munich this week we had the opportunity to discuss a very interesting workflow they have been extensively involved with over the last several years.

Dealing with unexploded munitions has remained a challenge for Germany since the end of WWII. Here is a great article outlining the challenge.

However, mapping based on aerial photography has been a success in many regions throughout the country. The workflow involves processing legacy aerial photography taken during or shortly after the war. The imagery is often of poor quality, and may even be lacking the fiducial marks required to establish interior orientation. GEOSYSTEMS tackled this by building an application to reconstruct fidicual locations. After that, they run through the classic photogrammetric workflow and produce stereo images and digital orthos. This enables both 2D and 3D workflows for capturing the location of bomb craters. After munitions locations have been mapped, the data can then be entered in a GIS. Next comes the practical application: in the areas that have implemented this workflow, the database is checked prior to new construction. This helps uncover the potential locations for unexploded munitions prior to construction - which is a life-saving application.

Here is an example of the 2D workflow: vectors of the bomb locations are collected in IMAGINE:


Files with the XY coordinates of the potential bomb locations can also be created:


For the 3D stereo feature extraction process, here's another example depicting stereo extraction in Stereo Analyst for ArcGIS:

Fidicial Marks: An Explanation

I tend to get a lot of visitors finding their way to this blog by searching for information on fiducial marks. So, why not ouline what they are and why they are important?

In the context of aerial photography, fiducial marks are small registration marks located along the outside of an aerial photograph. There are typically four or eight numbered marks, which look like this (note: this is number 1):



So what are they for? During the camera calibration process, the positions of the fiducial marks are measured precisely. The principal point of the image can be derived from the intersection of the fiducial marks. See here for an interesting paper on the development of camera calibration methods. The results of the camera calibration are usually stored and reported in a document (typically a USGS camera calibration report in the USA), and some organizations include their camera calibration reports on their web-sites: here is an example.

Fidicial marks are also important in the early stages of the photogrammetric processing, when the system establishes the relationship between "film" coordinate space and "pixel" coordinate space (solving for interior orientation). This process involves either physically or automatically measuring the fiducial marks.

Finally, it is important to note that fidicial marks are only used in film cameras. You'll only see them on scanned aerial photography. Digital cameras use different camera calibration techniques, and the USGS has a research lab on digital camera calibration research.

Sensor Spotlight: Leica Geosystems ADS80 Airborne Digital Sensor

I’ve touched on ADS40 sensor technology in a few different posts, but the focus of today is the new ADS80 sensor. The ADS80 is a pushbroom airborne sensor that was formally announced and highlighted at the ISPRS conference this past summer in Beijing.

See here for an interesting discussion on the transition to from analogue to digital processing as well as pushbroom sensors. The new sensor represents a solid advancement, and arguably delivers the best quality imagery of any of the commercial large-format airborne sensors.

But what is the difference between the ADS80 and the previous version, the ADS40? This post will cover the differences and explore some of the specific technical improvements.
Firstly, there are several overall design improvements. There is a new design for the data channel with overall data throughput increasing from 65 MB/s to 130MB/s. The fastest cycle time has increased from 800Hz to 1000Hz (this allows for faster flying speeds than previously possible), and there are data compression options for 10 bit, 12 bit, as well as the raw data.

The ADS80 also features a new design for the Control Unit (called CU80). The new Control Unit is smaller and contains an integrated slow for two Mass Memory units. Here what the new CU80 looks like:

The new system also introduces a new solid state Mass Memory unit (MM80). This size is smaller and weights only 2.5 kg, and has a few different options for data storage modes: single volume, joined volume, and in-flight backup. The joined volume of the two MM offers the greatest data throughput as well as the largest storage capacity, which is ideal for large-area collection missions.

For direct georeferencing applications, IPAS comes embedded in the control unit as well. This is critical for image collection missions in remote areas where ground control may not be possible: this is important in applications such as disaster mapping, remote area mapping (e.g. certain pipeline mapping applications) as well as surveillance operations.

Overall, the system weight has been reduced by 26 kg! It also contains new periphery equipment, including a new GPS/GLONASS Antenna.

Lastly, what does the imagery look like? In short, it looks fantastic. Here’s a sample of imagery collected at 5cm GSD over Lucern, Switzerland earlier this year (click on the image for a larger view).
More information, including both a product brochure and data sheet, is available from the Leica Geosystems website. Also note that new a new software package for ground processing, called XPro, will also be released quite soon.

Special thanks to Ruediger Wagner, ADS Product Manager at Leica Geosystems, for providing details on the new sensor.

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!

Historic Aerials: Visualizing Change Over Time

There's been a fair bit written on Historic Aerials already, but check out the new article in V1 Magazine. I've been a fan of Historic Aerials site for awhile now, and a few weeks ago we had a chance to interview them. A lot of the comments from the discussion are encapsulated in the article, and overall it was quite interesting to hear Jim and Brett talk about the trials and tribulations of working with historic photography. They are heavy LPS users (mainly for orthorectification and image processing) and have processed massive quantities of orthos while building content for the site.

It's easy to spend a lot of time on the site: if you want to see a good example of suburban Atlanta's development check out our ERDAS office location:

5050 Peachtree Corners Circle, Norcross GA. There's imagery from 1955, 1960, 1972, 1978, 1988, 1993, and 2007. When looking at the older images it becomes apparent that the entire area was developed over the past 20-30 years.

Make sure you check out the "Compare Two Years" option as well - it allows you to compare a second year to your currently loaded year and then adds a "swiping" capability to the viewer. Very cool!