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Intro. To GIS Post Midterm Review March 25 th , 2013

Intro. To GIS Post Midterm Review March 25 th , 2013. Vector vs. Raster. Vector Data. Vector data represented by coordinates Points have X and Y coordinate pairs Lines (arcs) connect two or more points Polygons are a series of connected lines. Raster Data.

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Intro. To GIS Post Midterm Review March 25 th , 2013

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  1. Intro. To GISPost Midterm Review March 25th , 2013

  2. Vector vs. Raster

  3. Vector Data • Vector data represented by coordinates • Points have X and Y coordinate pairs • Lines (arcs) connect two or more points • Polygons are a series of connected lines

  4. Raster Data • Many cells make up a raster grid/image • Size of cells can vary • Each cell has a value • Think of a digital photograph… • Pixels = cells

  5. Cont’d • Question 4 and Question 5: Page 132 • Question 6 ??? Com’on

  6. REVIEW: Scale?

  7. Datums • Reference surfaces used for mapping • Tied to a specific ellipsoid • Based on many precise measurements • Both horizontal (e.g. ellipsoid) and vertical (Geoid) datums • Common US horizontal (2D) datums: • North American Datum (NAD) 1927 or 1983 • World Geodetic System of 1984 – U.S. DOD (used worldwide)

  8. Earth Shape: Sphere and Ellipsoid

  9. Earth Models and Datums

  10. Horizontal Datums: Ellipsoids • Bulge at the equator • Flattened at the poles • A theoretical surface which fits the Earth best (globally/regionally) • Semi-major axis • Semi-minor axis b a Flattening

  11. Ellipsoid vs. Geoid • Ellipsoids are idealized (mathematical) models • Geoids are more complex and representative (of the Earth surface) • Different ellipsoids work better in certain parts of the world • In North America, usually WGS 1984 or GRS 80

  12. Types of Projections • Planar (Azimuthal) • Cylindrical (Mercator) • Conical

  13. Review: Transverse Mercator (TM) Central Meridian Central Meridian changes with the specific region for which the projection is done

  14. Isopleth/Contour Map

  15. Question 14 • Based on USGS standards, a 1:24,000 map scale has 24ft horizontal accuracy

  16. Earth Observing (EO)/Infrared (IR) Remote Sensing Systems • Space borne • CORONA • IKONOS / Geoeye (high spatial res.) • Quickbird / WorldView (high spatial res.) • Landsat/ SPOT (medium spatial res.) • MODIS/VIIRS/AVHRR (low spatial res.) • Airborne (UAV) • AVIRIS • Predator • Global Hawk

  17. Scale and Generalization • Yellow generalization for smaller scale maps

  18. 03_19_Figure Spatial Resolution

  19. 03_03_Figure Need at least 4 satellites to find X, Y, Z, and error in receiver’s clock (Time)

  20. Differential GPS (DGPS) x+5, y-3 x+30, y+60 x-5, y+3 Receiver DGPS Receiver DGPS Site Realtime (RTK) True coordinates = x+0, y+0 Correction = x-5, y+3 DGPS correction = x+(30-5) and y+(60+3) True coordinates = x+25, y+63

  21. Sources of Errors When Positioning with GPS • Standard Positioning Service (SPS ): Civilian Users • SourceAmount of Error • Satellite clocks: 0.5 to 1 meter • Orbital errors (ephemeris):< 1 meter • Ionosphere: 5.0 to 10.0 meters • Troposphere: 0.5 to 1 meter • Receiver noise: 0.3 to 1.5 meters • Multipath: 0.6 to 1.0 meters • Selective Availability (SA) Does not exist any more • User error: Up to a kilometer or more • Errors are cumulative and increased by DOP. • Note that the numbers are not current (absolute). However, you can get a feel for which errors are more significant than the other (relative).

  22. Difference between Almanac and Ephemeris • The satellites broadcast two types of data, Almanac and Ephemeris. • Almanac data is coarse orbital parameters for all SVs. Each SV broadcasts Almanac data for ALL SVs (Satellite Vehicles). This Almanac data is not very precise and is considered valid for up to several months. • Ephemeris data by comparison is very precise orbital and clock correction for each SV and is necessary for precise positioning. EACH SV broadcasts ONLY its own Ephemeris data. This data is only considered valid for about 30 minutes. The Ephemeris data is broadcast by each SV every 30 seconds. • When the GPS is initially turned on after being off for more than 30 minutes, it "looks" for SVs based on where it is based on the almanac and current time. With this information, appropriate SVs can be selected for initial search. When the GPS receiver initially locks onto a SV, the Garmin display then shows "hollow" signal strength bars. At this time, the Ephemeris data has yet to be completely collected. Once the ephemeris data is collected from EACH SV in turn, the associated signal strength bar will turn "solid" black and then the data from that SV is considered valid for navigation. If power is cycled on a GPS unit, and when turned back on, the Ephemeris data is less than 30 minutes old, lock-on will be very quick since the GPS does not have to collect new Ephemeris data.

  23. Poor Satellite Geometry N W E S

  24. Spectral Resolution

  25. REVIEW: Spectral Resolution • Electromagnetic Spectrum Reflectance (%)

  26. Transformation types: Affine • The affine transformation function is: • x’ = Ax + By + Cy’ = Dx + Ey + F • where x and y are coordinates of the input layer and x’ and y’ are the transformed coordinates. • The C and F parameters control shift in origin (translation) • A, B, D, E control scale and rotation • their values are determined by comparing the location of source and destination control points. • Scales, skews, rotates, and translates • 6 unknowns( A,B,C,D,E,F) so a minimum of three “displacement links” required • Little benefit from more than 18-30 links • The most common choice

  27. Vector Data and Topology • Topology • The arrangement for how point, line, and polygon features share geometry • Or knowledge about relative spatial positioning • Two types of vector models exist in a GIS • Geo-relational Vector Model • Arc Coverage (has topology) >>> format: binay • Shape files (no topology) >>>> format: *.shp, *.shx, *dbf, etc. • Object-based Vector Model • Includes classes and geodatabases >>> format: *.mdb

  28. Organizing Attribute Data • Flat Files • Hierarchical • Relational (databases) • Object-oriented (database)

  29. Organizing Attribute Data • Relational (What is commonly used in GIS) • Various tables (databases) are “linked” through unique identifiers

  30. Non-spatial Data • Or Attributes (for a vector dataset) Field (Attribute)--- It could be either numeric or text) Record The Shape Field/Object ID tells about the type of vector feature (point/polygon/line)… It is where the coordinates are also stored (you do not see them here)

  31. With Only Three Satellites Visible to the receiver purple dots are intersections of 2 satellites XX add our one second error to the third receiver… define area of solutions …receivers calculate best solution (add or subtract time from each satellite) …circle from 3rd satellite cannot intersect where other two do

  32. Fourth Satellite position determined from multiple pseudo-range measurements 4 satellites…three (X, Y, Z) dimensions and time when clock offsets are determined, the receiver position is known

  33. Q 33 and 34 • Page 30 • 1 degree longitude: 111km * cos (phi)=81.2 km • Page 31

  34. State Plane

  35. 02_11_Figure UTM Coordinate System

  36. 02_11_Figure Datum and UTM • NAD83: (North American Datum) produced in 1983 • Q38 • Page 38 • Q39 • Blocking of signal due to the trees/branches, etc.

  37. Q 42

  38. Radiometric Resolution

  39. 03_21_Figure Radiometric Resolution • Radiometric res= where m is the number of bits • Tells us about the dynamic range of pixel numbers in an image

  40. 03_21_Figure Jpeg Vs. Tiss • Jpeg is a lossy format • Jpeg does not inherently carry geo-coordinates

  41. Spectral Resolution

  42. Q 48 • Land cover: nominal • Temperature: interval • Building numbers: ordinal/nominal • Population: ratio • Check your email for further discription

  43. Query: Select by Attributes • Or Structured Query Language (SQL) • Enter criteria for one or more fields • Numeric values =,<,>,<> • Nominal values = ‘text’ • Change criteria or narrow results based on additional criteria

  44. REVIEW: Joins and Relates • Many datasets are available in tabular format • Excel (.xls, .xlsx), comma-spaced values (.csv), text • Tables can be imported to ArcMap and linked points, lines, or polygons using a common ID

  45. REVIEW: Joining Tables • Tables downloaded as text or CSV may need to be opened and saved as Excel files first • First row of table should contain short headers with no special characters (or spaces, ideally) • Table must have an ID that matches geography

  46. REVIEW: One-to-one • A one-to-one relationship means that each record in one table has only one matching record in another table

  47. REVIEW: Many-to-one • Many-to-one means multiple records in the table match to one record in another table

  48. REVIEW: Joining Tables • Right-click the spatial data which will have the table joined to it, click Joins and Relates, then Join… • Choose the table and the common ID fields

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