11 Replies Latest reply: Aug 9, 2010 2:16 PM by 632600 RSS

    GeoRaster performance: Compressed vs Uncompressed

    632600
      I tried to read compressed and uncompressed GeoRaster. The different in the performance confused me. I expected better performance for compressed raster, because Oracle needs to read in few times less data from hard drive (1:5 in my case). However, reading uncompressed data is approximately twice faster. I understand Oracle needs to use more CPU for uncompressing data. But I thought that saved time of reading data would be more than time for uncompressing a raster.

      Did anybody compare the performance?

      Thanks,

      Dmitry.
        • 1. Re: GeoRaster performance: Compressed vs Uncompressed
          Jeffrey Xie
          Dmitry, what methods do you use to read the georaster data? Do you read the raster blocks directly from blob or do you call sdo_geor.getrastersubset?

          thanks

          Jeffrey
          • 2. Re: GeoRaster performance: Compressed vs Uncompressed
            632600
            I use applications like ArcMap,FME Universal Viewev, Oracle Map Builder. All of them have different performance, but always a JPEG raster is slow.

            Thanks,

            Dmitry.
            • 3. Re: GeoRaster performance: Compressed vs Uncompressed
              Jeffrey Xie
              Dmitry,

              I do not know how ArcMap and FME do it. Oracle MapBuilder always calls sdo_geor.getRasterSusbet with a polygon geometry (could be in any coordinate system) to query the database. In general applications, because the query window is random, getRasterSusbet would find out the relevent raster blocks (in this case compressed) and then decompress, mosaic, clip and then return the result into the client for display. as you see there is an extra decompressing operation and that's why. I/O is very fast when you use securefiles for the georaster block storage.

              thanks

              jeffrey
              • 4. Re: GeoRaster performance: Compressed vs Uncompressed
                615755
                Dmitry,

                Have tried QGIS? It works pretty fast to me when I compare compressed and uncompressed, JPEG or Deflate GeoRaster.

                Regards,

                Ivan
                • 5. Re: GeoRaster performance: Compressed vs Uncompressed
                  632600
                  Hi Ivan,

                  I don't think I will use QGIS.
                  Could you just share your experience, what is faster, how much faster ?


                  Regards,

                  Dmitry.
                  • 6. Re: GeoRaster performance: Compressed vs Uncompressed
                    615755
                    Dmitry,

                    You can try for yourself. QGIS is a free-open-source-software.

                    QGIS uses GDAL to access raster and vector data and there is a plugin called "Oracle Spatial GeoRaster", or just oracle-raster, to deal with GeoRaster. To access Geometries you don't need to activate the plugin, just select Oracle as your database "type" in the Add Vector Layer dialog box.

                    Displaying GeoRaster work pretty fast, as long as you have created pyramids. Yes, there is a little delay when the GeoRaster is compressed but that is because GDAL request the data to be uncompressed and QGIS has no clue about it.

                    Wouldn't be nice to have a viewer that used the JPEG as it is?

                    Regards,

                    Ivan
                    • 7. Re: GeoRaster performance: Compressed vs Uncompressed
                      632600
                      Hi Ivan,

                      I don't see the option 'Oracle' in type. There are ODBC, ESRI, OGDIVectors, PostgreSQL and MySQL only.
                      I downloaded it from http://www.qgis.org/wiki/Download#Standalone_Installer_.28recommended_for_new_users.29 , Windows, Standalone Installer.

                      What is wrong?



                      Thank you,

                      Dmitry.
                      • 8. Re: GeoRaster performance: Compressed vs Uncompressed
                        615755
                        Since you are using Windows, you should try get the OSGeo4W installer from here:

                        http://trac.osgeo.org/osgeo4w/

                        See how to use the installer here:

                        http://www.oracle.com/technetwork/database/enterprise-edition/gdal-howto-compile-windows-128267.txt

                        That doesn't include QGIS but you can find on "desktop applications" list.
                        • 9. Re: GeoRaster performance: Compressed vs Uncompressed
                          632600
                          Hi Ivan,

                          I installed the appication. I added 2 layer - geometry and raster from Oracle. I can see geometry but I don't see the raster. Zoom to layer extent do nothing.

                          BTW, seems the application doesn't recognize the projection(Nad83/UTM zone 17N). I manually set the projection in Project property and in the property of the layer, but id doesn't help.

                          Thanks,

                          Dmitry.

                          Oops, I got it. I have to use Select Oracle GeoRaster button instead of Add Vector Layer.

                          Edited by: Dmitry on Aug 5, 2010 2:42 PM
                          • 10. Re: GeoRaster performance: Compressed vs Uncompressed
                            615755
                            Dmitry,

                            What indicates that it doesn't recognize NAD83/UTM17N ?

                            A blank screen could means that you need to change the symbology or select bands.

                            Can you runs this command on your GeoRaster and copy back the report to us?

                            gdalinfo geor:user/pwd@db,rdt,rid -mdd oracle

                            Thanks.

                            Ivan
                            • 11. Re: GeoRaster performance: Compressed vs Uncompressed
                              632600
                              I don’t see an Oracle raster when I add it via “Layer”,”Add vector layer”.
                              I don’t think it is invisible; it rather was not loaded at all.

                              I can see the same raster when I use “Select Oracle GeoRaster” button.

                              So, it wasn't the projection issue.

                              BTW, when I try to open raster with pyramids the application just silenly close. I have no an issue with not pyramided rater.

                              Thanks,

                              Dmitry.