Kamis, 29 Januari 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).

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