On December 2, 2014, DAT/EM and PCI Geomatics hosted a joint webinar about using PCI Geomatica 2014 and DAT/EM LandScape to generate a highly accurate DEM. For more information about LandScape, visit www.datem.com/landscape.
We received several questions after the webinar. Below are the questions and answers.
Q: I have Summit Evolution Professional, do I need to purchase LandScape?
A: Summit Evolution and LandScape are independent products and may be purchased separately. LandScape can run without the companion vector editors, using the DATEM Drawing Tools as a simple vector editor. Adding DATEM Capture to LandScape adds the capability to use the full functionality of ArcGIS, MicroStation, or AutoCAD.
Summit Evolution, the digital stereoplotter, comes equipped with one version of Capture, thus when running Summit and LandScape together the Capture becomes available to LandScape. When used this way it is not necessary to purchase Capture unless enabling another variety of Capture.
Q: What is the advantage of Lidar over aerial imagery? Especially considering the resolution part?
A: Each has its own distinct utility and we recommend consulting with a service provider for a solution tailored to your own requirements. A brief summary of the differences follows:
Lidar is primarily a topographic tool. Its GSD can be quite small relative to that derived from imagery, and in areas of dense foliage or other cover the odds of finding the surface are often better than with stereo imagery. Multiple return information can improve the information revealed in a survey. It is this multiple-return information that most think of as a “point cloud”, although single-return (surface) points constitute a point cloud also. However, Lidar is monochromatic (wavelength generally = 1064nm) and therefore carries no color information. Albedo, or reflectance, can help to generate an image.
Aerial imagery is an imaging tool. Stereo imagery can be used for modeling the surface; the definition of that surface depends on the opacity of any foliage or other intervening objects. Because of the crispness of imagery, it is usually preferred when defining object edges. Furthermore, inherent color information is useful for object identification and other traditional imagery uses such as vegetation health monitoring. Images are often used to guide point cloud classification. Like Lidar, surfaces generated from imagery may be treated as a “single-return” point cloud, but usually those result from automatic terrain extraction tools such as PCI AutoDEM. Some modern automatic tools can approach the GSD of the imagery. Orthoimagery is a very popular end product and usually requires both an image source and a terrain source, both of which can be derived from aerial photography.
As is generally true with all things, the more detailed the data the higher the cost. Lidar data can be as detailed as imagery, but the costs are higher. Generally speaking, imagery has a smaller GSD when acquired at the same flying height.
Q: Where (or IS IT POSSIBLE) to get some free LiDAR datasets for training students purposes using PCI 2014? Or do we have to buy some? How much does each cost, generally?
A: Possible sources of free lidar data are local governments, service vendors, and equipment manufacturers. The sample data used in this demo of Toronto were received from Optech. Often a nominal charge is levied to cover the costs of reproduction. It is difficult to determine the costs associated with acquiring new lidar since so much depends on the project specifications such as GSD, AOI, distance from base, availability of ground control
Q: How can Lidar hold the top edge of buildings when creating the orthos? The raw photo building roof would not line up with the Lidar unless the building falls dead center in the nadir.
A: This is referred to as a “true ortho”, in which buildings stand up straight and areas occluded during the rectification of a single image are filled in with other images in the project. The tops of the buildings can be determined in a couple of ways: using not one but two raw images in stereo to measure and digitize the outlines in 3D, or find the closest point in the 3D point cloud and use that to define the outline of the building.
The reason they do not line up in a single image is due to the parallax inherent in the viewing process. Using two images in a stereopair and viewing in stereo can take advantage of this parallax to measure height or elevation. This method can precisely measure the coordinates of building edges and corners, although objects on the roof (and all other objects, if desired) must be individually measured.
Using Lidar data, the contents and general shape of the roof are collected; being able to resolve them depends on the Lidar footprint relative to the size of the object. Edges are not defined as crisply, however, as with comparable imagery.
The result of using these when creating a true ortho will be something like this: Using imagery as a source for manually defining the edges will be more time-consuming but likely to be more precise in the long run. Using an automatic DEM extraction tool can produce a surface model (DSM) result similar to Lidar but based entirely on imagery. Using Lidar will likely be quicker but still requires processing to refine and classify the point data. It is often necessary to collect vectors defining the buildings anyway.
Q: How is it going to handle DSMs of different resolution?
A: Depending on the end result desired, it can make little difference, but generally speaking one wants to have a DSM of similar resolution to the target ortho. The primary effect of coarse granularity of a DSM is to flatten the terrain used to correct the image. Thus high objects will be displaced too little, and low objects too much, which can result in u. Thus the choice of an appropriate DSM is important.
LandScape and Summit both have the Point Translator tool which can be used to merge, tile, resize, and otherwise manipulate point files of various types.
Q: is LandScape a standalone module?
For more information about LandScape, visit www.datem.com/landscape.
DAT/EM Systems International was presented the 2014 Governor's North Star Award for International Excellence for export of services (intellectual property). The award honors DAT/EM Systems International for its significant contribution to Alaska's trade, investment, and international relations. The Honorable Sean Parnell, Governor of the State of Alaska, presented the award during a private reception on Tuesday, November 25, 2014.
DAT/EM Systems International has been developing photogrammetric software since 1987 and specializes in 3D stereo viewing and feature data collection software. By continually expanding market share and changing with international technology trends, DAT/EM Systems International remains a leader of photogrammetric mapping development and a unique part of the Alaska industry.
Pictured above (from left to right): Stan Moll, International Business Development Manager, DAT/EM Systems International; Kierra Marnet, Office Manager, DAT/EM Systems International; Alissa Oder, Technical Documentation and Support, DAT/EM Systems International; Jeffrey Yates, General Manager, DAT/EM Systems International; The Honorable Sean Parnell, Governor of the State of Alaska; Jennifer Gunderson, Photogrammetric Software Engineer, DAT/EM Systems International; Tara Tate, Marketing Coordinator, DAT/EM Systems International; Robert Bredlie, Senior Photogrammetric Software Engineer, DAT/EM Systems International.
For more information about DAT/EM Systems International, please visit www.datem.com.