Processing GeoData for CEDEUS

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This pager provides logging info and processing instructions for CEDEUS data.

Processing Aerial Images from SECTRA

• downlading zip files with ecw images from:
  • 2007: http://www.sectra.gob.cl/datos_e_informacion_espacial/gran_santiago/ortofoto_2007.html
  • 2012: http://www.sectra.gob.cl/datos_e_informacion_espacial/gran_santiago/ortofoto_2012.html
• unpacking the zip files with winrar on Windows to have finally the ecw files (I did this with winrar, as it allows to select multiple zips easily and giving one output dir)
• converting the ECW files to GeoTIFF:
  • use QGIS under Windows (installed with OSGeo installer) to convert the files. Important, QGIS for Windows comes with ecw support, while on Ubuntu it has to be installed first... so its much easier
  • I used the QGIS function: Raster > Conversion > Translate (Convert Format) which utilized gdal_translate (of course ;)
  • apply batch processing
  • for the 16cm/px data it makes sense, I think, to use jpg compression - but see next note below. This returns the smallest files, in comparing to other compression modes: e.g. for file 166.ecw : Packbits: 1.6 GB, Deflate: 527 MB, JPG: 214 MB . Using jpg compression should be ok, as the ecw files are compressed lossy anyway (using the wavelet transform), and we have images = non-category data.
  • it looks like javax.imageio used by GeoServer can't read the jpg compressed TIFF, so I converted the jpg Tiff file to Tiff file with deflate compression using QGIS. The gdal command for that looks something like this:

    gdal_translate -co COMPRESS=DEFLATE -co PREDICTOR=2 -co ZLEVEL=9 -of GTiff ./tiff_jpgcompress/101.tif ./tiff_deflate/101d.tiff

• generate an index file:
  • the idea is to create a shapefile containing an image index, to be uploaded to GeoNode
  • in QGIS I used the function Raster > Miscellaneous > Tile Index... which utilizes gdaltindex