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Applied Cartography and Introduction to GIS GEOG 2017 EL

Applied Cartography and Introduction to GIS GEOG 2017 EL. Lecture-3 Chapters 5 and 6. Metadata. Metadata provide information about geospatial data. They are therefore an integral part of GIS data and are usually prepared and entered during the data production process.

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Applied Cartography and Introduction to GIS GEOG 2017 EL

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  1. Applied Cartography and Introduction to GISGEOG 2017 EL Lecture-3 Chapters 5 and 6

  2. Metadata • Metadataprovide information about geospatial data. They are therefore an integral part of GIS data and are usually prepared and entered during the data production process. • Metadata are important to anyone who plans to use public data for a GIS project.

  3. Conversion of Existing Data • Data conversion refers to the mechanism for converting GIS data from one format to another. • Data conversion includes direct translation and use of neutral format.

  4. MIF to Shapefile Tool in ArcGIS

  5. Neutral Format Translation

  6. Creating New Data • A variety of data sources and methods can be used to create new data: • Remotely sensed data • Field data (survey data and GPS data) • Text files with x-, y-coordinates • Digitizing using a digitizing table • Scanning • On-screen digitizing

  7. Bearing and Distance

  8. GPS Data

  9. Portable GPS Receiver

  10. Elevation from GPS

  11. Digitizing Table

  12. Manual Digitization Many GIS packages have a built-in digitizing module for manual digitizing. The module is likely to have commands that can help move or snap a feature (i.e., a point or line) to a precise location in relation to another feature either in the same layer or a different layer.

  13. Snapping Tolerance

  14. Snapping Tolerance

  15. Scanning • Scanningis a digitizing method that converts an analog map into a scanned file, which is then converted back to vector format through tracing. • Results of tracing depend on the robustness of the tracing algorithm that is built in the GIS package. Examples of problems that must be solved by the tracing algorithm include: how to trace an intersection, where the width of a raster line may double or triple; how to continue when a raster line is broken or when two raster lines are close together; and how to separate a line from a polygon.

  16. Binary Scanned File

  17. Raster Error in Scanned Image

  18. Geometric Transformation • Geometric transformationis the process of using a set of control points and transformation equations to register a digitized map, a satellite image, or an air photograph onto a projected coordinate system. • In GIS, geometric transformation includes map-to-map transformation and image-to-map transformation.

  19. Transformation Methods Different methods have been proposed for transformation from one coordinate system to another. Each method is distinguished by the geometric properties it can preserve and by the changes it allows.

  20. Types of Geometric Transformations

  21. Affine Transformations

  22. Control Points • Control points play a key role in determining the accuracy of an affine transformation. • Selection of control points for a map-to-map transformation is relatively straightforward. What we need are points with known real-world coordinates. • Control points for an image-to-map transformation, also called ground control points, are points where both image coordinates (in rows and columns) and real-world coordinates can be identified. GCPs are selected directly from a satellite image; the selection is not as straightforward as selecting four tics for a digitized map.

  23. Transformation Steps

  24. RMS Error The root mean square (RMS)error is a common measure of the goodness of the control points. It measures the deviation between the actual (true) and estimated (digitized) locations of the control points.

  25. RMS Error Interpretation • If a RMS error is within the acceptable range, we usually assume that the transformation of the entire map is also acceptable. • This assumption can be quite wrong, however, if gross errors are made in digitizing the control points or in inputting the longitude and latitude readings of the control points.

  26. Location Errors

  27. Location Errors

  28. Pixel Resampling Resamplingis a process that fills each pixel of the new image derived from an image-to-map transformation with a value or a derived value from the original image.

  29. Resampling Methods • Three common resampling methods are nearest neighbor, bilinear interpolation, and cubic convolution. • The nearest neighborresampling method fills each pixel of the new image with the nearest pixel value from the original image. • The bilinear interpolationmethod uses the average of the four nearest pixel values from three linear interpolations. • The cubic convolutionmethod uses the average of the 16 nearest pixel values from five cubic polynomial interpolations.

  30. Resampling

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