Friday, January 30, 2009

Value-Added GeoPDFs Part 2

In case you want to check out the example GeoPDF from the previous post, I have now uploaded a couple versions of it to the Adobe site. The file size is fairly big, so I created two versions:

Higher quality (compression factor of 60) at 119MB.

Lower quality (compression factor of 15) at 55MB.

In both cases the imagery looks decent, but the shaded relief in the 55MB version shows the effects of over-compression. If you haven't had a look at it before check out as well - 5GB of online file storage are available for free!

To adjust the layers, open the files in Adobe Reader and click on the "Layers" icon on the left side. The bands are as follows:

Bands 1/2/3 = RGB orthomosaic
Bands 4/5/6 = Shaded Relief
Band 7 = DSM

In the example below the Shaded Relief bands are loaded, and as you can see they can be adjusted in a number of combinations.

Thursday, January 29, 2009

Data Presentation: Value-Added GeoPDFs

When I initially heard about GeoPDF I thought it sounded like a good enabling technology for people without advanced geospatial expertise or access to the appropriate software. After all, anyone can view a PDF. Typically I thought of it in the context of viewing RGB orthophotos... Fast-forward to the present: lately I've been thinking about ways of presenting fused data, and this is where GeoPDFs came to mind. In particular I wanted to present terrain and image data.

For input data I started with some edge-matched orthophotos of Sligo, Ireland and processed XYZ LIDAR data of the same area (data courtesy of OSi). I processed the data in LPS and IMAGINE, which basically involved importing the LIDAR data and converting it to the IMAGINE IMG format, and then creating a shaded relief map out of it. For the imagery I mosaiced several tiled input images into a single orthomosaic. The processing resulted in three products: an RGB image file, a shaded relief image, and a DEM. To put them all together I used the "Layer Stack" function in IMAGINE, which resulted in a 7-layer 8bit IMG file.

Next, I converted the IMG to a GeoPDF. This was a painless process and produced a 7-layer PDF file. My input file covers a fairly broad area and was a few gigs (2.7GB to be precise) in size so I used a JPEG compression quality factor of 60, which for visual analysis creates a fairly sharp-looking image in a PDF format with a much-reduced size of 122MB. This allowed me to open up the image in Adobe Reader and view the image.

Because the first three layers of my image are the RGB orthomosaic, this is what is displayed when opening the PDF in Adobe Reader. I also have the GeoPDF Toolbar (recently renamed to TerraGo Desktop) loaded as well for various measurement and manipulation functions:

(click any of the screen captures for larger views)

By clicking on the "Layers" button I could adjust the band combinations for RGB to display the shaded relief.

It was also possible to display various fused results. In this example I am displaying Red and Green from the orthomosaic and then loading the DEM into the Blue channel. This means the colors are skewed but the benefit is that you can see the image feature details and also get a notion of the high-relief areas. In this case high relief shows up as dark blue, and the absence of blue indicates low-relief (e.g. the upper left areas).

Note that many kinds of band combinations/visualizations are possible with this fused product.

Many thanks to Adam Estrada for assisting with the GeoPDF part of this workflow. I also plan on making the dataset available soon (I'll hopefully get it uploaded tonight).

Monday, January 26, 2009

Terrain From Imagery

In 2009 the need for accurate high resolution terrain data is only growing. One can see increasing numbers of applications that use terrain all over the geospatial industry and beyond. Part of the reason for the proliferation of terrain and applications that use it stems from increased usage in all methods of collecting and creating terrain. The SRTM mission provided course-resolution terrain for large portions of the world. LIDAR sensors continue to sell briskly, and of course automatically-generated terrain from triangulated oriented images (stereo pairs) continues to grow as increasing numbers of sensors capture image data.

Automatic terrain generation, which involves producing TINs and grids by correlating XYZ points from a pair of overlapping oriented images, is nothing new. In the context of softcopy photogrammetry the technology is over a decade old, and at ERDAS we have produced automatic terrain extraction solutions since the release of OrthoBase Pro back in 2001. Since then most photogrammetry practitioners have worked automatic terrain generation into their production workflows, particularly as a source for orthophoto generation. While I believe sensor fusion (capturing optical and LIDAR data simultaneously) will have an increasing role in the future, the reality is that automatically-generated terrain is also likely to play an important role for years to come. Why? Because data is becoming captured at increasingly high resolution and software solutions are evolving in their ability to generate corresponding high-density terrain data. A good example is the ADS80 sensor from Leica Geosystems. It can capture imagery at a 5 centimeter pixel resolution. Data captured at this resolution allows for very dense (and accurate) automatically extracted terrain.

In the photogrammetry group at ERDAS we’ve been putting effort into new techniques for automatic terrain extraction from imagery. Specifically we are looking at automating as much as possible, updating terrain extraction algorithms, and supporting modern IT infrastructures by adding distributed processing capability. After all, generating massive terrain datasets can require some serious computer power.

The image below shows terrain with a 10 centimeter density (post spacing) processed as an LAS file and displayed in GeoCue's PointVue LE viewing software (designed for visualizing LIDAR data). Color is based on elevation, so you can easily see the buildings and other surface features. Using a LIDAR viewer as a QC tool helps because of the density of the data.

In the image below I've rotated the view and applied intensity shading. This displays the detail quite well: it is possible easily discern the buildings, roads, crops and vegetation.

And a view of another area:

Sunday, January 25, 2009

Low-Cost Satellite Mapping

An article on BBC News website from Thursday outlines a company, Surrey Satellite Technology Limited (SSTL), that plans on developing a sensor capable of sub-meter resolution. I don't see any mention of a timeline or any information on the SSTL web-site, but the news article claims the new system is calleld ART (Accuracy, Reach, Timeless).

With a price tag of $70 million it still isn't "cheap", but it is considerably less than than the $500 million it cost to build and launch GeoEye-1. Considering NGA paid half the cost, a low-cost system may make satellite remote sensing more commercially viable. Hence, it the news that SSTL has been purchased by EADS Astrium doesn't come as a surprise.

This is certainly a development to keep an eye on, as the project will have a great shot at success if the the lower development and launch costs translate into lower data costs for consumers.

Wednesday, January 21, 2009

3D PDF Generation

I thought I would write a "how-to" post after reading some recent coverage on 3D PDFs. There are a few different software packages that can generate 3D PDFs, but I will cover the workflow using LPS, PRO600 Fundamentals, and Bentley PowerMap. The actual 3D PDF generation is done with PowerMap (also supported in MicroStation). Aside from photogrammetric mapping it is also possible to build a model from guesstimating building dimensions or designing a model from scratch.

To produce the 3D PDF below, I performed the photogrammetric pre-processing in LPS and then extracted 3D building vectors in PRO600 Fundamentals (which runs on top of Bentley PowerMap) via stereo feature extraction. After that, the steps are:

1) From PowerMap set the View extent to the area to be exported.
2) Choose File > Print. This opens the dialog below.
3) Ensure "Plot to 3D" is checked.
4) Choose Settings > 3D Plotting: you may want to change some settings such as the background color and a number of advanced settings.
5) Choose File > Print (from within the Print menu) when you're ready to save out the 3D PDF.

Click on the image below to download the 3D PDF I generated. I didn't get into any sophisticated modeling, but the tools within PowerMap and MicroStation will allow for creation of highly realistic models.

This post also gives me a chance to try out Scribd: check out the 2D PDF I exported from PowerMap as well, with imagery as a backdrop. Personally I like the zoom and pan functionality as well as full-screen mode: a nice alternative to viewing in Acrobat...
Los Angeles Ortho and Vectors See here for some more 3D PDF examples from the Bentley MicroStation V8i page.

Monday, January 19, 2009

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 's recent post (and particularly the video) on the methodology and benefits of using the Vermont 2008 NAIP imagery in a GIS.

Monday, January 12, 2009

Leica XPro: A First Look...

Last week I had the opportunity to learn more about Leica XPro, the new ground processing software for the ADS40/ADS80 airborne sensor. You may have seen the press release from ISPRS last summer announcing the partnership between Leica Geosystems and North West Geomatics Ltd.

Some background information: GPro has been the post-processing software for the ADS40 pushbroom sensor since it's introduction to the market several years back. Coupled with ORIMA, it produces various image products ranging from raw images to triangulated stereo pairs and digital orthophotos.

Leica XPro is the successor to GPro, and is a completely new software package that offers some innovative tools for streamlining the ADS workflow.

Here are a few of the benefits that impressed me:

- There's a new viewer that is blazing fast. Since ADS sensors collect long "pixel carpet" strips of imagery, the file sizes can be fairly large (which can be a big advantage when it comes time for image mosaicking). This allows for a quick quality control check right after the data is downloaded. The viewer allows RAW images to be previewed prior to georeferencing and also supports virtual on-the-fly viewing of L1 (georeferenced) imagery. The viewer also has the ability to apply radiometric corrections on the L1's. Here's what the viewer looks like with an ADS80 FCIR image loaded:

- There's been a complete overhaul of the aerial triangulation methodology. Like GPro, ORIMA-M is the backbone of the triangulation system, however XPro has created a "grey-box" version of it. ORIMA's CAP-A bundle adjustment software is still embedded with the system, but the user interface has been completely updated. There is a completely new system for point measurement (featuring the new viewer technology), and improvements have been made in autocorrelating points across images. You can also load a DSM of the project area (GTOPO30 comes with the software, or you can use your own), as displayed below:

- Also new for the triangulation system is an innovative color coded quality "heat map" of sorts, which allows for an interactive analysis and refinement of weak areas (e.g. point review, new automatic point measurement runs, etcetera). The number of APM points required for a solution has also been dramatically reduced.

Once the imagery is triangulated, XPro can also perform distributed orthorectification processing. Like GPro, the system is also uses CONDOR.

Here are some images of varying resolutions over the same area showing what you can expect out of the ADS80. Feel free to click on the images below to view the full screen captures.

Friday, January 9, 2009

From the Leica Geosystems Headquarters

I've been spending this week at the Leica Geosystems HQ in Heerbrugg, Switzerland.

It's been a great opportunity to learn more about the latest software (XPro) and hardware developments (the ADS80). However before getting to that, I wanted to show a few photos of some of the older gear that is on display here.

Here is a Kern PG 2 stereoplotter, which was in production between 1960 and 1985.

Here is a Wild B8 stereoplotter, in production between 1961 and 1972.

And finally, below you can see a Cyrax laser scanner alongside a Wild A-6 analogue stereoplotter (1940-1953).

The A-6 was used quite extensively in WWII (along with the A-5). For an interesting perspective on how photogrammetric hardware development was spurred on during war-time, check out the "The Sky Spies" at the Smithsonian National Air and Space Museum. A colleague in Atlanta recently visited and has shared his photos here (thanks Ray!). It is interesting to see how much of the technology came out of Germany, the USA and Japan. In particular check out the last photo: a Japanese "motion picture camera gun"!