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Geomatica OrthoEngine Orthorectifying WV-1 and WV-2 Data

Rigorous and RPC Modeling WorldView–1 launched on September 18, 2007. It offers panchromatic imagery at a very high resolution of 50 cm at nadir. The key benefits of this highly detailed imagery are in the sectors of precise map creation, change detection and in-depth image analysis. Data is distributed by DigitalGlobe (www.digitalglobe.com). WorldView-2 launched on October 8, 2009. It is a successor of the WV-1 satellite which provided very high resolution PAN and MSS imagery. WV-2 offers panchromatic imagery of 46 cm resolution at nadir and 52 cm at 20 degree off-nadir. MSS imagery is provided at 1.84m resolution in 8 bands, which makes WV-2 the most spectrally diverse commercially available dataset. Distribution and use of imagery at better than 0.50m GSD PAN and 2.0m GSD MSS is subject to prior approval by the U.S. Government. PCI OrthoEngine can process Basic L1B and OrthoReadyStandard2A level of WV data products. The following is a brief tutorial showing the use of Geomatica OrthoEngine for Orthorectifying WorldView -1 (Basic 1B) and WorldView -2 (ORS2A) raw imagery with the Rigorous Model and Rational Polynomial Coefficients (RPC). If the user is supplied with OrthoReadyStandard2A level of data with RPCs, then it is recommended to use RPC modeling instead of Rigorous Modeling. Note: The processing steps for WV-1 and WV-2 data are the same with the exception of stitching and assembling. OrthoReadyStandard2A tiles will need to be assembled inside OrthoEngine. Alternately QBASMBLE in the Algorithm Librarian/EASI can also be used. Level 1B data will need to be stitched in OrthoEngine. Alternately STITCH in the Algorithm Librarian/EASI can also be used.

Initial Project Setup The example below shows how to process OrthoReadyStandard2A data. Open Geomatica 2013’s OrthoEngine application To do this through the Geomatica toolbar, click on the OrthoEngine button

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Start OrthoEngine and click ‘New’ on the File menu to start a new project. Give your project a ‘Filename’, ‘Name’ and ‘Description’. Select ‘Optical Satellite Modeling’ as the Math Modeling Method. Under Options, select ‘Toutin's Model’ or ‘Rational Function (Extract from image)’. After accepting this panel you will be prompted to set up the projection information for the output files, the output pixel spacing, and the projection information of GCPs. Enter the appropriate projection information for your project.

Rational Function (RPC Model)

Data Input For Rigorous or RPC modeling within Geomatica OrthoEngine, the user should have WorldView-1 or WorldView-2 “Basic (L1B) Imagery” or OrthoReadyStandard2A. “Standard Imagery” products are pre-processed to a further extent than Basic Imagery products. Since they have a correction already applied, Standard Imagery products cannot be Orthorectified. For more information on these products, please refer to Digital Globe's official website www.digitalglobe.com WorldView data is delivered in Geotiff 1.0, NITF 2.0, and NITF 2.1 formats, which are fully supported by Geomatica OrthoEngine. The data is also delivered with a number of support files

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(ATT, EPH, GEO,IMD, RPB, STE, TIL and XML). Please note that these support files should be located in the same directory as the image data while reading the data.

Rational Function (RPC Model) Select the ‘Data Input’ option from the ‘Processing Step’ drop down and click on “Open a new or existing image”. This step will convert the file to ‘.pix’ format.

Assembling OrthoReadyStandard2A tiles will need to be assembled inside OrthoEngine. Alternately QBASMBLE in the Algorithm Librarian/EASI can also be used. For OrthoReadyStandard2A tiles, if the filenames contain R1C1, R2C1, etc. the files must be assembled using ‘Utilities | Assemble Tiles…’ in OrthoEngine. Due to the size limitations, WorldView OrthoReadyStandard images may be delivered to you as image tiles with RPC data. The RPC data is used with the Rational Functions math model and covers the entire scene, not the individual tiles. Therefore, you must reassemble the tiles into one scene before using it in your project. OrthoReadyStandard2A PAN and MSS Datasets are re-sampled exactly on top of each other. So it is recommended to work on a PANSHARP product instead of individual PAN and MSS Datasets. Use ‘Utility |Merge/Pansharp Multispectral Image’ functionality to do pansharpening inside OrthoEngine.

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GCP Collection - Rational Function (RPC Model) At this stage an Orthorectified image can be directly generated in the absence of any GCPs. The model will be computed based on the supplied RPCs. If GCPs are available, they can be added into the project using the GCP/TP Collection Processing step. The model will be automatically computed, and GCPs can be reviewed through the Residual report. It is recommended to use ZERO order RPC adjustment (i.e. minimum of 1 GCP) for WV-1 and WV-2 imagery. A FIRST order RPC adjustment (I.e. minimum of 3 GCPs, well distributed in entire image) is recommended for QuickBird imagery (http://www.pcigeomatics.com/pdfs/WorldView-1.pdf)

Generate Ortho The final step is to ‘Schedule Ortho Generation’. Proceed to the ‘Ortho Generation’ processing step and select the file(s) to be processed. Select an appropriate DEM file and set other processing options before generating the final orthorectified image. Tip: Specify a sampling interval of 4 and enter a background value of the selected DEM to speed up the ortho process.

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Initial Project Setup The example below shows how to process Basic L1B data. Open Geomatica 2013’s OrthoEngine application To do this through the Geomatica toolbar, click on the OrthoEngine button Start OrthoEngine and click ‘New’ on the File menu to start a new project. Give your project a ‘Filename’, ‘Name’ and ‘Description’. Select ‘Optical Satellite Modeling’ as the Math Modeling Method. Under Options, select ‘Toutin's Model’ or ‘Rational Function (Extract from image)’. After accepting this panel you will be prompted to set up the projection information for the output files, the output pixel spacing, and the projection information of GCPs. Enter the appropriate projection information for your project.

Toutin’s Model (Rigorous)

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Data Input For Rigorous or RPC modeling within Geomatica OrthoEngine, the user should have WorldView-1 or WorldView-2 “Basic (L1B) Imagery” or OrthoReadyStandard2A. “Standard Imagery” products are pre-processed to a further extent than Basic Imagery products. Since they have a correction already applied, Standard Imagery products cannot be Orthorectified. For more information on these products, please refer to Digital Globe's official website www.digitalglobe.com WorldView data is delivered in Geotiff 1.0, NITF 2.0, and NITF 2.1 formats, which are fully supported by Geomatica OrthoEngine. The data is also delivered with a number of support files (ATT, EPH, GEO,IMD, RPB, STE, TIL and XML). Please note that these support files should be located in the same directory as the image data while reading the data.

Toutin’s Model (Rigorous Model) After successful extraction of data to your hard disk, proceed to the ‘Data Input’ processing step in OrthoEngine. Select the ‘Data Input’ option from the ‘Processing Step’ drop down and click on the ‘Read CD-ROM data’ button (Please note that we are treating this data as if it is on CD-ROM, even though it is actually located on the hard disk).Choose ‘WORLDVIEW’ as the ‘CD Format’ and select your TIFF or NITF image file. Press the appropriate channel buttons (1 for a PAN image). Specify an appropriate output ‘PCIDISK filename’, a ‘Scenedescription’, and a ‘Report filename’. This step will convert the file to ‘.pix’ format, and add the information needed for modeling.

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Stitching Level 1B data will need to be stitched in OrthoEngine. Alternately STITCH in the Algorithm Librarian/EASI can also be used. For level 1B data, if the filenames contain R1C1, R2C1, etc. the files must be stitched using ‘Utilities | Stitch PIX Format Image Tiles…’ in OrthoEngine. The stitching operation merges different tiles, obtained from the same orbit on the same day, into one complete scene. It rebuilds the orbital data for the whole strip to maintain the ephemeris information. Also it merges all raster tiles and recalculate stitched image RPCs from individual RPCs of the image tiles. Stitching automatically stores final RPCs as a binary segment in the output PIX file.

Collect GCPs and Tie Points -Toutin’s Model (Rigorous Model)

Select the ‘GCP/TP Collection’ processing step. GCP collection can be done using various options: ‘Manual Entry’, ‘Geocoded Images/Vectors’, ‘Chip Database’ or a ‘Text File’. For the Rigorous model, a minimum of six accurate GCPs per image (or more, depending on the accuracy of the GCPs and accuracy requirements of the project) are required. After collecting the GCPs, select the ‘Model Calculation’ Processing Step and click on ‘Compute Model’. Check the ‘Residual Report’ panel (under the Reports processing step) to review the initial results.

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Generate Ortho The final step is to ‘Schedule Ortho Generation’. Proceed to the ‘Ortho Generation’ processing step and select the file(s) to be processed. Select an appropriate DEM file and set other processing options before generating the final orthorectified image. Tip: Specify a sampling interval of 4 and enter a background value of the selected DEM to speed up the ortho process.