TrueOrtho with 3D Feature Extraction

Transcription

1 TrueOrtho with 3D Feature Extraction PCI Geomatics has entered into a partnership with IAVO to distribute its 3D Feature Extraction (3DFE) software. This software package compliments the TrueOrtho workflow which is presently available in the GXL 2013 product line, and will be coming to Geomatica The following diagram is the TrueOrtho workflow utilizing FeatureXTract to generate the Digital Surface Model (DSM) necessary for TrueOrtho production. Page 1

2 Modules GXL Aerial comprises several modules as either a base-package or add-on workflows. In some cases the tasks are run individually, with others being chained together into an end-to-end workflow. To fully process TrueOrtho imagery, the following GXL-A modules are required, along with the QA Bundle Tools to preform DEM and vector editing. Airphoto Ingest Module DEM Extraction from Airphoto module DEM Export Module DEM Generation Module TrueOrtho Mosaic Preparation Mosaic Generation Also required QA Bundle Tools (Focus, EASI) FeatureXTract FeatureXTract is a standalone software package that allows the user to generate 3D building models. FeatureXTract is a geospatial site-modeling system composed of both automated and semi-automated tools. These allow you to rapidly extract 3D buildings and related features from aerial and satellite imagery. FeatureXTract employs a simple split-screen interface eliminating the need for active stereo displays in 3D feature extraction. Using FeatureXTract you can quickly extract accurate 3D site models and export them for use in a variety of applications, including digital terrain database generation. With FeatureXTract, building an urban environment is now simple, rapid, and most importantly accurate. Workflow Operations To process TrueOrtho imagery, a DSM is required which consists of a bare earth Digital Terrain Model (DTM) and 3D building features. These operations can be performed with the GXL 2013 and the Geomatica 2014 suite of software. Page 2

3 Data Ingest The workflow begins with the ingestion of the aerial data. GXL-A supports all digital frame sensors in tiff or jpeg format, with appropriate metadata (IO, EO, AT). This data is ingest and linked PIX files are generated with an associated math model created from the metadata. DEM Extraction The DEM Extraction module allows you to automatically create Digital Surface Models (DSMs) from overlapping stereo images. Image correlation is used to extract matching pixels in two overlapping images and then use the sensor geometry from a computed math model to calculate x, y, and z positions. DSM extraction allows epipolar generation, extraction, geocoding and the creation of absolute or relative DEMs. The output of this module is both a DSM and DTM. A DSM represents the elevation surface, including objects such as buildings and trees, whereas a DTM represents a bare-earth elevation surface. Because of this, using a DTM to perform standard orthorectification generally produces better results. But a DEM extracted from overlapping images is a DSM; this should be converted to a DTM and edited before being used for orthorectification. Using the 3D DEM Editor in the QA Bundle tools, you can edit the DSM to smooth out irregularities and create a more accurate model, and in turn, generate more accurate orthorectified images. Page 3

4 Figure 1: Aerial image, DSM and edited DTM. The resultant DTM can be merged with 3D building models to generate a DSM that can specifically be used for TrueOrtho production. The 3D buildings are generated through the FeatureXTract software. For standard orthorectification, it is important to note that the DTM resolution should be 1:3 or 1:4 to that of the original imagery. TrueOrtho of course will require a higher resolution DSM, but this can be accomplished in the DEM Export and Generation modules. The bare-earth elevation surface resolution does not need to be as fine as the building models, therefore the DTM can be generate at a lower resolution, and then interpolated at a higher resolution when the building models are added. Page 4

5 FeatureXTract FeatureXTract 3.0 is an easy-to-use feature extraction and 3-D modeling software system developed under the defined objective of improving the process workflow. Its sole purpose is to maximize the efficiency of extraction and complex modeling by providing accurate and simplified software tools. Through its tight integration with geo parameters and standards, FeatureXTract allows users to explore, discover, and accurately model 3-D spatial content with utmost confidence. Page 5

6 Inputs for the FeatureXTract program are identical to the GXL, where imagery and the associated metadata are ingested into the working project for 3D building creation. Optionally, you can use the DTM generated from the DEM Extraction module for a more accurate surface elevation, or a low resolution default DTM is provided with the software. The 3D building models are exported to an ESRI shape (.shp) file format that can be merged with the DTM in the GXL DEM Generation module. Subsequently you may have to edit the shp file to clean up any geometry errors, such as overhanging polygons (i.e. multiple roofs). DEM Export & Generation Generation of the final DSM is a two-step process. The edited DTM first needs to be converted to a point data file such as.las (LASF, ASPRS LIDAR Data Exchange Format). The second step is to regenerate the DSM with the point file and 3D building shape file. The DEM Generation module reads multiple vector files containing points, breaklines, contours, valleys, ridges, and cliffs, and generates a raster digital elevation model (DEM) by interpolating elevation values of points, contours, and 3-D structure lines. The module then generates a.pix,.tif or JPEG2000 file. The output resolution of the DSM can be of any size. For TrueOrtho processing, it is highly recommended that the DSM be of the same resolution or higher than that of the output image resolution. If the resolution is too coarse, the building may become distorted or appear jagged along the straight edges. The generated DSM can be used by the TrueOrtho module. TrueOrtho A true ortho image is an orthorectified image with geometric corrections applied to both bare Earth surfaces and above-ground objects, such as buildings and bridges, in their exact planimetric locations. Often, buildings appear to lean when they are not directly under the camera. The two adverse effects of this are that the building rooftops are portrayed in an erroneous location, and Page 6

7 ground features are occluded by buildings. The True Ortho module corrects these effects by moving the pixels corresponding to the building rooftops to their proper position and filling any obscured areas with pixels from overlapping images. The True Ortho module is composed of two processing steps: partial generation of ortho images, and occlusion filling. First, the module generates orthorectified images with occluded areas detected. This processing step takes a text file as input, and outputs scene description XML files. The input text file contains references to the input data set and various parameter settings. Each output scene description XML file refers to the output partial ortho image, index map, elevation map, and some parameter values corresponding to each input image. The occluded areas are identified on these ortho images but are unfilled. Second, the module fills occluded areas in the orthorectified images with data from adjacent images. This processing step takes as input the scene description XML files and an optional list defining the subset to process, and outputs final ortho images with their obscured pixels compensated for by selecting and sorting among their adjacent ortho images. Page 7

8 Mosaic Preparation The Mosaic Preparation module performs all the necessary pre-mosaicking procedures required to produce a high-quality image mosaic. These procedures include color balancing, cutline generation, image normalization, and scene order specification. The output is a mosaic source image list file and a directory that will contain all the necessary information to manipulate the images before they are added to the mosaic. You may load the results into the PCI Mosaic Tool for further quality control, or proceed directly to mosaic generation. If desired, run the separate Localized Adaptive Enhancement module before generating the final mosaic. When applying an enhancement to large images such as mosaics, no single look-up table (LUT) can be applied to the entire image without overexposing or underexposing different areas in the image. To address this problem, the Localized Adaptive Enhancement module divides the input image into a grid of tiles and computes a separate geocoded LUT for each tile. These GeoLUTs are then used to enhance the input image. The generated LUTs are stored in a separate file for later use, providing the ability to generate a low-resolution preview of the final image with enhancements applied, and decreasing the amount of time required for the final enhancement. Mosaic Generation The Mosaic Generation module automatically produces a mosaicked image product using a source image list XML file as input. The source image list XML file is generated during the execution of the Mosaic Preparation module. Among other options, the Mosaic Generation module allows you to define how the output mosaic will be tiled (if at all), which channels to output, and the mosaic's name, blend width, and image format type. Page 8