Friday, June 13, 2008

Short Hiatus

I'll be traveling (and generally away from computers) for the next five weeks so the lights will be out at The Fiducial Mark for the next little while. I'll be back in action by late July and will be reporting from a different location: see below for details!

In the meantime, check out e-planet for the latest posts from some other folks at ERDAS.

Wednesday, June 11, 2008

Leica Geosystems Chinese Earthquake Press Release

This press release was sent out nearly a week ago. I wanted to highlight it since I haven't seen much about it anywhere else and I think it is a great example of how rapid response applications can save lives (and hey, there's photogrammetry involved too). I won't rehash the story here since you can read about it in the press release, but I would like to highlight a few key points.

We hear a lot about how aerial photography is used for rapid response mapping, but an important consideration to the type of airborne sensor employed for such applications. On reflection, the ADS40 is a great camera for this sort of thing. Why? The fact that it is a pushbroom sensor offers a great advantage. This means it collects a "pixel carpet" instead of the typical 4Kx4K or 9Kx9K frame camera. This is critical for rapid mapping applications because the image analyst (for example, the person who saw the SOS in the press release image) doesn't have to waste time loading frames or performing a large mosaicking job with a lot of seams. They can either review the strip directly or run a quick and dirty mosaicking job that doesn't require much in terms of seam edits.

Make sure you check out the image associated with the press release (link below). It is fairly high-res when you zoom in and the earthquake damage is noticeable. You can also see from the bottom of the image that the screen capture was taken from ERDAS IMAGINE.

At any rate, I will write a Sensor Spotlight on the ADS40 in the future and highlight some of the other applications it is suited for..

Saturday, June 7, 2008

Cell Arrays in LPS

In LPS we use a spreadsheet like tool called a “Cell Array” for managing and manipulating data in several parts of the software package. The first place you see a Cell Array is when you load a project in the LPS Project Manager: it is the list at the bottom with one row per image. Generally Cell Arrays are used for different purposes in the various places they are embedded, so I will highlight a few of them here.

In the LPS Manager, the Cell Array lists all the images and also provides an image-by-image status. There are status columns (either red for incomplete or green for complete) for Pyramid Layer, Interior Orientation, Exterior Orientation, if there is a DTM associated with the image, an Ortho associated with the image, and whether the image is “online”. That is, does the image reside where the blockfile has referenced it. There is also an “Active” column that flags each particular image for inclusion in various processing operations (e.g. running pyramid generation or APM on just the active images). From the Cell Array you have the ability to select images, perform a criteria selection, and delete the selection (remove images from the project).

One of the powerful capabilities is to use the criteria selection plus the “formula” option to activate or deactivate images. A trick here is to use the criteria selection to select a group (e.g. Image ID > 30) and then activate or deactivate your selection group using the “formula” Cell Array option. Once you have a selection set, right click on the “Active” column heading and choose the “Formula” option. Type in “1” and hit Apply to activate all the images. Likewise you can type in “0” and hit apply to deactivate all the selected images (see the screenshot below).

Another place with a Cell Array is the Frame Editor. When you are in “Edit All Images” mode, the image, sensor name, orientation parameters and other information are all made available in the cell array. This is a useful place for setting the image orientation status. For example, if you want to import orientation parameters from GPS/IMU data you can cut and paste the six parameters in, set the status to “fixed” and immediately view the images in stereo (assuming there aren’t any issues with the orientation parameters). It is also possible to Import and Export data (among other things) by right clicking on the column heading. For example, orientation parameters can be exported by selecting the images, highlighting the headings for the orientation parameters, then right-clicking on the column heading and choosing "export". See the second screenshot below for an example.

A Cell Array is included in the LPS Stereo Point Measurement tool as well. This Cell Array can be useful for managing tie and control points. By saying “managing”, I mean performing tasks such as:

  • Importing GCP points
  • Exporting tie points
  • Defining the point status
  • Activating and Deactivating points
  • Deleting points

For example, if you ran Automatic Point Measurement and then proceeded through triangulation, you can export your tie points as XYZ data and then use that as the basis for a “quick and dirty” surface model. Automatic Terrain Extraction is a better choice (where you can use tie and control points as seed data), but at least this allows you some flexibility.