Image Registration Exercise ESPM 5295

Transcription

1 Background: We often digitize data from orthorectifed aerial photographs. These photographs have been processed to remove tilt and terrain errors to the level practical and required by the original contract. They still contain residual error, and often miss-align. Error levels vary, but with technologies available since the late 1990 s, positional accuracies are generally from 0.5 to 1.5 times the pixel dimensions of the delivered products. Therefore, an image with 1 meter resolution (cells) will often have an average spatial error of 0.5 to 1.5 meters. You generally cannot much improve on the average accuracy over an entire image. However, you often can for a sub-area, with a simple linear transformation, improve the average accuracy. In addition, when pulling information from multiple images, taken at different dates and resolutions, you often want to co-register images so that the data are consistent. In this exercise we will co-register orthoimages. You will use the provided high accuracy GPS data collected by former students (2103 & 2014) for the St. Anthony Park practice area. Each of you will register images using the provided GPS data and subsequently to images you have already registered. Assignment First, review the image registration exercise in Week 4 for FNRM 3131 or FNRM Next select the sub-area you of your choice in the image. You can only use areas covered by the Previously_Collected GPS control points found in...skills\imageregistration\previous_student_control. You need to select an area approximately 20 hectares. Try and figure out how you can estimate a 20 ha area in ArcMap. There are several ways. (if you have to Use the \template\about_20_hectares.shp as your guide.) You will perform this image registration, using the GPS data as your CONTROL and image stp2006 as the target image. You are registering the stp2006 to the true GPS locations provided. As with all our work, we will create output in the Zone 15N UTM NAD83 (COR96) coordinate system. Maintain the pixel size on the registered image, using a bilinear interpolation when resampling (ArcMap Georeferencing Rectify). The.IMG format for your registered output is perhaps your best choice. Then register the nga2012, msp2006, and cir2008 to the stp2006 image you created initially. While you register the images remember to save the Link Tables and note RMSE values. Also remember that the images you register are only corrected for your area of interest (the 20 ha). This process of improving the accuracy of an image can only be done on small sub-areas. Finally use ArcCatalog to document your work by creating the Metadata for each layer. Remember you can create one master Metadata and the copy it to the 2 nd 3 rd and 4 th layers. Then making the slight adjustments to the copied Metadata records. Read ArcGIS Help on Metadata; it is very good.

2 To be submitted via Moodle You should create a map of the registered stp2006 image, with your registration (truth) points displayed, and include a legend, north arrow, scale bar, and title. Also include the RMSE from the stp2006 image registration process. In addition, you must turn in the Control Point/Residual tables (saved Link Tables) for all four registrations, including the individual errors and RMSEs for all al four images. Please Combine the all the Link Tables and the Map in to one, multi-page PDF, if possible. Also turn in the Metadata files for each of your registered images. The Metadata files are the ones with the extension.xml For example stp2006r.img.xml Turn it PDF s and XML s in the Moodle DropBox

3 Notes and Examples Example of sub-area selected and Link Table shown: Example of Rectify Output process:

4 In ArcCatalog (Customize >ArcCatalog Options) Use the ISO Metadata Implementation Specification (a standard format) In ArcCatalog select your registered image and left click then select Description In ArcMap, ArcCatalog view select the registered image and right click then select Item Description. This is where you get at reading or writing Metadata. (ArcMap, ArcCatalog view shown below)

5 On the Description tab, select Edit Fill in (or delete) the red X s Complete as much as you can; be creative. Pretend this is a real project. You will need to do this for your final project.

6 When done SAVE and then Export Then for the next image registration output layer Import from this stand alone XML file. It will bring in all your previous material and you can just change the name and a few other items.