3.16.2010

DESKTOP GIS: MAPPING THE PLANET WITH OPEN SOURCE TOOLS

PART 1 NOTES:

common formats
•Shapefiles(.shp)
•GeoTIFForTIFFwithworldfiles(.tif,.tfw)
•JPEGwithworldfiles(.jpg,.jpw)
•GPSdata(.gpx)

other vector formats
•ArcInfoBinaryCoverage
•ArcInfoInterchangeFile(.e00
•MapInfo(..tab,.mid,.mif)
•SDTS,adatatransferstandardforbothvectorandrasterdata1
•TopologicallyIntegratedGeographicEncodingandReferencing
(TIGER)data,usedanddistributedbytheU.S.CensusBureau
•DigitalLineGraphics(DLG)

other raster formats
•ERMapperCompressedWavelets(.ecw)
•ErdasImagine(.img)
•DigitalElevationModels(.dem)
•JPEG2000(.jp2,.j2k)
•Multi-ResolutionSeamlessImageDatabase(MrSID)(.sid)
•GTOPO30,aglobaldigitalelevationmodel(DEM)derivedfroma
numberofrasterandvectorsources

Note: use an OSGIS software that uses GDAL/OGR for accessing raster and vector data (GRASS and QGIS)

data format deliverable over the web: Open Geospatial Consortium website http://www.opengeospatial.org
WebMappingService(WMS),

PostGIS
-Creating a POSTGis-enabled database:

WebFeaturesService(WFS),
WebCoverageService(WCS).

STANDARDIZE FORMATS USED FOR BETTER DATA MANAGEMENT AND FOR LOGICAL STRUCTURING AND STORAGE
    -provid a metadata that will document our assets
    - convert data into standard format for better functionality (i.e. shapefile into PostGIs or GRASS layer with geoprocessing capability, ex. in buffering)

Buffering in PostGIS- simple SQL Query
    in GRASS - use v.buffer command or buffer module in QGIS-GRASS toolbox.
for PostGIS conversion: improve data management by givng a "portal" to our data, but also being OGC compliant
            - provides spatial functions in Simple Features Specification for SQL
            - getting a whole batch of spatial functions for querying relationships between features, transform between projections and create new features.

GRASS - various vector-and-raster-processing tools
    •Line-of-sightanalysis
    •Unionandintersectionoflayerstocreateanewlayer
    •Mergingrasterdata
    •Mathematicaloperationsongrids
    •Contouring

CONVERSION OPTIONS:
Line of Sight Analysis
    - you need a DEM for height.
    - r.los in GRASS doesnt work for geographic coords so use Albers Projection instead.
    - r.mapcalc command allows you to do arithmetic operations on the cells in raster layers
    - use gzip -d to unzip files

HYDROLOGIC MODELING
    - r.lake
    - r.out.mpeg

CREATING HILLSHADES
    - use a DEM and GRASS r.shaded.relief module
    - a 4x exaggeration is better than defaul 1x exaggeration
    - colorizing the hillshades:
    MERGING DEMS
        - use r.patch command (use g.region first to set GRASS region)

        ex project: melting the ice sheets and determining sea level rise by r.lake
    CLIPPING RASTERS WITH GRASS
    The steps to clip a raster are as follows:
        1.Create a vector map to be used as the area of interest.
        2.Convert the vector map to a raster map.
        3.Use the new raster map as a mask for clipping.
        4.Create the newly clipped raster using raster algebra.
        5.Clean things up

- GRASS conversion: page 96
- PostGIS conversion:
- GDAl/OGR utilities

OpenSource Spatial Database : PostgreSQL with PostGIS - more mature and feature-rich, for spatial processing and queries
                MySQl -for storing spatial features

            *both complies with OGC, but most fully implemented in PostgreSQL/PostGIS

MBR- minimum bounding rectangle or BBOx(bounding box), extent

PosGIS- creating template using commandline tools

Using PostGIS and QuantumGIS

Projection DATA problems
- big difference in alignment, PROJECTION PROBLEM
- small difference - (500m) - DATUM PROBLEM

Creating Data
1. Digitizing p. 122 - heads-up digitizing, needs to georeference image after digitizing to have it belong to a fix geographic coordiante system and avoid overlapping.
            -easy digitizing using r.to.vect, clean up to many vectors with v.clean with tool=rmarea to clean up noise in the image.

2. Importing text from files - use a delimited text and get it easily imported in GRASS and QGIS
                QGIS - supports import points only
                GRASS - all feature types in GRASS vector model.
        -CREATING A LAYER FROM DELIMITED TEXT FILE ON QGIS
        - PREPROCESSING TEXT FOR INPUT, using a ruby script for creating a delimited file.
        - CONVERTING DATA
            -E00 interchange file to GRASS to all other format or use GDAL/OGR suite of tool

GEOPROCESSING
•Projection
•Line-of-sightanalysis
•Watershedmodeling
•Hillshading
•Clippingfeatures
•Morecompleximporting
•Gridalgebra

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