Optimizing, publishing and styling GeoTIFF data

Styling with CSS

The CSS extension module allows to build map styles using a compact, expressive styling language already well known to most web developers: Cascading Style Sheets.

The extension is available on GeoServer only. The standard CSS language has been extended to allow for map filtering and managing all the details of a map production. In this section we’ll experience creating a few simple styles with the CSS language.

Styling raster data

• Go to the srtm_boulder layer details page and click on Editing Tools > Style > Edit

  

• Add a new Style

  

• Select CSS and click on the + button

  

• Put a name like CSS Raster and click on Save

  

• Modify the style you just created

  

• From the panel, switch to the advanced editor

  

• Insert the following CSS, notice the changes directly on the map, and Save

    * {
       raster-channels: auto;
       raster-color-map:
         color-map-entry(black, 0, 0)
         color-map-entry(green, 1500)
  
         color-map-entry(yellow, 2000)
         color-map-entry(maroon, 3000)
         color-map-entry(white, 4000);
    }
  

  

• The * at the beginning means that we will apply the rules at any zoom level; let’s add a rule to show the raster only above a certain scale denominator

    [@scale > 75000] {
       raster-channels: auto;
       raster-color-map:
         color-map-entry(black, 0, 0)
         color-map-entry(green, 1500)
  
         color-map-entry(yellow, 2000)
         color-map-entry(maroon, 3000)
         color-map-entry(white, 4000);
    }
  

  

• Try to zoom in and out by checking the scale denominator; notice the raster appearing and disappearing accordingly

  

Nice Map with Hillshading

In this section we are going to create a hillshade raster computed from the srtm DEM of Boulder. We will use the GDAL utilities to do that, and in particular the gdaldem one, which has several options available.

Once we created the hillshade, we will add it to GeoNode, provide a nice style and then merge all together on a nice map.

• Go to the terminal and move to the folder /opt/data/sample_data/pretty_maps/data/boulder/

• Run the gdaldem utility with the following options

    gdaldem hillshade -z 5 -s 111120 srtm_boulder.tiff srtm_boulder_hs.tiff -co tiled=yes
  

  

  The z parameter exaggerates the elevation, the s parameter provides the ratio between the elevation units and the ground units (degrees in this case), -co tiled=yes makes gdaldem generate a TIFF with inner tiling. We’ll investigate this last option better in the following pages.

• That will create a new GeoTIFF called srtm_boulder_hs.tiff

• Upload the new layer as user test_user1

  

• Edit the style for this layer too; a new CSS named Hillshade CSS

  

  

• Insert the CSS below and save

    [@scale > 75000] {
      raster-channels: auto;
      raster-color-map:
        color-map-entry(#000000, 0, 0)
        color-map-entry(#999999, 1)
        color-map-entry(#FFFFFF, 256);
      composite: 'multiply';
    }
  

  

  Note the “composite” vendor option, used to have the hillshading use a special color blending mode to get a better visual result compared to simple translucency

• Create a new Map and add the two raster layers just updated

  

• Highlight the srtm_boulder and the modify option

  

• Select the style tab, click on the CSS Raster style and Save

  

• Notice the legend has changed and so the rendering on the map for that layer

  

• Similarly go ahead and select the Hillshade CSS for the srtm_boulder_hs layer

  

• Adjust the overlays order and opacity and notice the map changing accordingly

  

• Zoom-in in order to highlight the details and the color effect enhanced by the hillshade

  

• Save the new map when done

  

Adding and Optimizing Raster Image Mosaics

An Image Mosaic is composed of a set of datasets which are exposed as a single coverage. The ImageMosaic format allows to automatically build and setup a mosaic from a set of georeferenced datasets. This section provides better instructions to configure an Image Mosaic.

Publishing an Image Mosaic

In this section we are going to publish on GeoNode a mosaic of aerial orthophotos through the GeoServer ImageMosaic store.

We will need to do some preparation first.

• Open a terminal and move to the folder /opt/data/sample_data/user_data; change the write permissions of the folder named aerial in order to allow the user to modify it

    cd /opt/data/sample_data/user_data
    sudo chmod -Rf 777 aerial
  

• Move to aerial and delete the files aerial.properties and sample_image.dat

    cd aerial
    rm aerial.properties sample_image.dat
  

• Create or edit a file named indexer.properties with the following contents

    vim indexer.properties
  

    Caching=false
    Schema=*the_geom:Polygon,location:String
  

• Create or edit a file named datastore.properties with the following contents

    vim datastore.properties
  

    SPI=org.geotools.data.postgis.PostgisNGDataStoreFactory
    host=localhost
    port=5432
    database=geonode_data
    schema=public
    user=geonode
    passwd=geonode
    Loose\ bbox=true
    Estimated\ extends=false
    validate\ connections=true
    Connection\ timeout=10
    preparedStatements=true
    create\ database\ params=WITH\ TEMPLATE\=postgis20
  

• Go to the GeoServer admin dahsboard; log in as an admin and click on Data > Stores > Add new store

  

• Select ImageMosaic form the list of the available Raster Data Sources

  

• Provide the following inputs on the ImageMosaic form

  • Name: Aerial
  • Title: Aerial
  • URL*: file:/opt/data/sample_data/user_data/aerial

  

• On the next windows, click on Publish and Save the layer

  

  

• Move to the GeoServer Layer Preview section and open the OpenLayers preview for the Aeriel layer

  

• We will suddenly notice two issues mainly:

  1. The load, pan and zoom is slow
  2. There are some black tiles filling the bounding box

  

Optimizing an Image Mosaic

• Open a terminal and move to the folder /opt/data/sample_data/user_data; change the write permissions of the folder named optimized in order to allow the user to modify it

    cd /opt/data/sample_data/user_data
    sudo chmod -Rf 777 optimized
  

• Move to optimized and delete the files optimized.properties and sample_image.dat

    cd optimized
    rm optimized.properties sample_image.dat
  

• Create or edit a file named indexer.properties with the following contents

    vim indexer.properties
  

    Caching=false
    Schema=*the_geom:Polygon,location:String
  

• Create or edit a file named datastore.properties with the following contents

    vim datastore.properties
  

    SPI=org.geotools.data.postgis.PostgisNGDataStoreFactory
    host=localhost
    port=5432
    database=geonode_data
    schema=public
    user=geonode
    passwd=geonode
    Loose\ bbox=true
    Estimated\ extends=false
    validate\ connections=true
    Connection\ timeout=10
    preparedStatements=true
    create\ database\ params=WITH\ TEMPLATE\=postgis20
  

• Add a new ImageMosaic Data Source like we already done before and provide the following parameters

• Provide the following inputs on the ImageMosaic form

  • Name: boulder_bg_optimized
  • Title: boulder_bg_optimized
  • URL*: file:/opt/data/sample_data/user_data/optimized

  

• On the next windows, click on Publish, change the name and title to boulder_bg_optimized and Save the layer

  

• Open the GeoServer Layer Preview and zoom/pan around, notice how faster is now the mosaic…

  

  The black tiles are still present.

• Let’s customize the mosaic options in order to improve the quality and remove the black tiles.

• Customize the ImageMosaic properties. Set the OutputTransparentColor to the value 000000 (Which is the Black color). Click on Save when done.

  

• Open the GeoServer Layer Preview, clear the browser image cache and zoom/pan around, notice the black tiles now gone

  

Image Mosaic Options

There are plenty of options that can be tweaked in order to further optimize an ImageMosaic.

• Accurate resolution computation: If true, computes the resolution of the granules in 9 points, the corners of the requested area and the middle points and take the better one. This will provide better results for cases where there is a lot more deformation on a subregion (top/bottom/sides) of the requested bbox with respect to others. Otherwise, compute the resolution using a basic affine scale transform.
• AllowMultithreading: If true, enables tiles multithreading loading. This allows to perform parallelized loading of the granules that compose the mosaic.
• BackgroundValues: Sets the value of the mosaic background. Depending on the nature of the mosaic it is wise to set a value for the no data area (usually -9999). This value is repeated on all the mosaic bands.
• Bands: a comma separated list of band indexes that allows to expose only a particular subset of bands out of a multiband source. Normally not configured by hand, but driven by SLD styling instead.
• ExcessGranuleRemoval: An option that should be enabled when using scattered and deeply overlapping images. By default the image mosaic will try to mosaic toghether all images in the requested area, even if some are behind and won’t show up in the final image. With excess granule removal the system will use the image footprint to determine which granules actually contribute pixels to the output, and will end up performing the image processing only on those actually contributing. Best used along with footprints and sorting (to control which images actually stay on top). Possible values are NONE or ROI (Region Of Interest).
• Filter: Filters granules based on attributes from the input coverage.
• Footprint Behavior: Sets the behavior of the regions of a granule that are outside of the granule footprint. Can be None (Ignore the footprint), Cut (Remove regions outside the footprint from the image. Does not add an alpha channel), or Transparent (Make regions outside the footprint completely transparent. Will add an alpha channel if one is not already present). Defaults to None.
• InputTransparentColor: Sets the transparent color for the granules prior to mosaicking them in order to control the superimposition process between them. When GeoServer composes the granules to satisfy the user request, some of them can overlap some others, therefore, setting this parameter with the opportune color avoids the overlap of no data areas between granules.
• MaxAllowedTiles: Sets the maximum number of the tiles that can be load simultaneously for a request. In case of a large mosaic this parameter should be opportunely set to not saturating the server with too many granules loaded at the same time.
• MergeBehavior: Merging behaviour for the various granules of the mosaic that GeoServer will produce. This parameter controls whether we want to merge in a single mosaic or stack all the bands into the final mosaic.
• OVERVIEW_POLICY: Policy used to select the best matching overview for a given target output resolution. Possible values are QUALITY (pick an overview with a higher resolution and downsample), NEAREST (pick the one with the closest resolution), SPEED (pick the closest one with lower resolution) and IGNORE (do not use overviews).
• OutputTransparentColor: Sets the transparent color for the created mosaic.
• SORTING: Allows to specify the time order of the obtained granules set. Valid values are DESC (descending) or ASC (ascending). Note that it works just by using DBMS as indexes.
• SUGGESTED_TILE_SIZE: Controls the tile size of the input granules as well as the tile size of the output mosaic. It consists of two positive integers separated by a comma, like 512,512.
• USE_JAI_IMAGEREAD: If true, GeoServer will make use of JAI ImageRead operation and its deferred loading mechanism to load granules; if false, GeoServer will perform direct ImageIO read calls which will result in immediate loading.

Introduction To Processing With GDAL Utilities

It’s a common practice to do a preliminary analysis on the available data and, if needed, optimize it, since configuring big datasets without proper pre-processing, may result in low performance when accessing them.

The previous examples show the difference between a non-optimized and an optimized mosaic, i.e. mosaics with pre-processed GeoTIFF granules or nor.

In this section, instructions about how to do data optimization will be provided by introducing some of the GDAL Utilities.

gdalinfo

This utility allows to get several info from the GDAL library, for instance, specific Driver capabilities and input Datasets/Files properties.

gdalinfo - Getting Drivers Capabilities

Being GeoTIFF a widely adopted geospatial format, it’s useful to get information about the GDAL GeoTIFF’s Driver capabilities using the command

gdalinfo --format GTIFF

Format Details:
  Short Name: GTiff
  Long Name: GeoTIFF
  Supports: Raster
  Extensions: tif tiff
  Mime Type: image/tiff
  Help Topic: drivers/raster/gtiff.html
  Supports: Subdatasets
  Supports: Open() - Open existing dataset.
  Supports: Create() - Create writable dataset.
  Supports: CreateCopy() - Create dataset by copying another.
  Supports: Virtual IO - eg. /vsimem/
  Creation Datatypes: Byte UInt16 Int16 UInt32 Int32 Float32 Float64 CInt16 CInt32 CFloat32 CFloat64

<CreationOptionList>
  <Option name="COMPRESS" type="string-select">
    <Value>NONE</Value>
    <Value>LZW</Value>
    <Value>PACKBITS</Value>
    <Value>JPEG</Value>
    <Value>CCITTRLE</Value>
    <Value>CCITTFAX3</Value>
    <Value>CCITTFAX4</Value>
    <Value>DEFLATE</Value>
    <Value>LZMA</Value>
    <Value>ZSTD</Value>
    <Value>WEBP</Value>
  </Option>
  <Option name="PREDICTOR" type="int" description="Predictor Type (1=default, 2=horizontal differencing, 3=floating point prediction)" />
  <Option name="DISCARD_LSB" type="string" description="Number of least-significant bits to set to clear as a single value or comma-separated list of values for per-band values" />
  <Option name="JPEG_QUALITY" type="int" description="JPEG quality 1-100" default="75" />
  <Option name="JPEGTABLESMODE" type="int" description="Content of JPEGTABLES tag. 0=no JPEGTABLES tag, 1=Quantization tables only, 2=Huffman tables only, 3=Both" default="1" />
  <Option name="ZLEVEL" type="int" description="DEFLATE compression level 1-9" default="6" />
  <Option name="LZMA_PRESET" type="int" description="LZMA compression level 0(fast)-9(slow)" default="6" />
  <Option name="ZSTD_LEVEL" type="int" description="ZSTD compression level 1(fast)-22(slow)" default="9" />
  <Option name="WEBP_LEVEL" type="int" description="WEBP quality level. Low values result in higher compression ratios" default="75" />
  <Option name="NUM_THREADS" type="string" description="Number of worker threads for compression. Can be set to ALL_CPUS" default="1" />
  <Option name="NBITS" type="int" description="BITS for sub-byte files (1-7), sub-uint16_t (9-15), sub-uint32_t (17-31), or float32 (16)" />
  <Option name="INTERLEAVE" type="string-select" default="PIXEL">
    <Value>BAND</Value>
    <Value>PIXEL</Value>
  </Option>
  <Option name="TILED" type="boolean" description="Switch to tiled format" />
  <Option name="TFW" type="boolean" description="Write out world file" />
  <Option name="RPB" type="boolean" description="Write out .RPB (RPC) file" />
  <Option name="RPCTXT" type="boolean" description="Write out _RPC.TXT file" />
  <Option name="BLOCKXSIZE" type="int" description="Tile Width" />
  <Option name="BLOCKYSIZE" type="int" description="Tile/Strip Height" />
  <Option name="PHOTOMETRIC" type="string-select">
    <Value>MINISBLACK</Value>
    <Value>MINISWHITE</Value>
    <Value>PALETTE</Value>
    <Value>RGB</Value>
    <Value>CMYK</Value>
    <Value>YCBCR</Value>
    <Value>CIELAB</Value>
    <Value>ICCLAB</Value>
    <Value>ITULAB</Value>
  </Option>
  <Option name="SPARSE_OK" type="boolean" description="Should empty blocks be omitted on disk?" default="FALSE" />
  <Option name="ALPHA" type="string-select" description="Mark first extrasample as being alpha">
    <Value>NON-PREMULTIPLIED</Value>
    <Value>PREMULTIPLIED</Value>
    <Value>UNSPECIFIED</Value>
    <Value aliasOf="NON-PREMULTIPLIED">YES</Value>
    <Value aliasOf="UNSPECIFIED">NO</Value>
  </Option>
  <Option name="PROFILE" type="string-select" default="GDALGeoTIFF">
    <Value>GDALGeoTIFF</Value>
    <Value>GeoTIFF</Value>
    <Value>BASELINE</Value>
  </Option>
  <Option name="PIXELTYPE" type="string-select">
    <Value>DEFAULT</Value>
    <Value>SIGNEDBYTE</Value>
  </Option>
  <Option name="BIGTIFF" type="string-select" description="Force creation of BigTIFF file">
    <Value>YES</Value>
    <Value>NO</Value>
    <Value>IF_NEEDED</Value>
    <Value>IF_SAFER</Value>
  </Option>
  <Option name="ENDIANNESS" type="string-select" default="NATIVE" description="Force endianness of created file. For DEBUG purpose mostly">
    <Value>NATIVE</Value>
    <Value>INVERTED</Value>
    <Value>LITTLE</Value>
    <Value>BIG</Value>
  </Option>
  <Option name="COPY_SRC_OVERVIEWS" type="boolean" default="NO" description="Force copy of overviews of source dataset (CreateCopy())" />
  <Option name="SOURCE_ICC_PROFILE" type="string" description="ICC profile" />
  <Option name="SOURCE_PRIMARIES_RED" type="string" description="x,y,1.0 (xyY) red chromaticity" />
  <Option name="SOURCE_PRIMARIES_GREEN" type="string" description="x,y,1.0 (xyY) green chromaticity" />
  <Option name="SOURCE_PRIMARIES_BLUE" type="string" description="x,y,1.0 (xyY) blue chromaticity" />
  <Option name="SOURCE_WHITEPOINT" type="string" description="x,y,1.0 (xyY) whitepoint" />
  <Option name="TIFFTAG_TRANSFERFUNCTION_RED" type="string" description="Transfer function for red" />
  <Option name="TIFFTAG_TRANSFERFUNCTION_GREEN" type="string" description="Transfer function for green" />
  <Option name="TIFFTAG_TRANSFERFUNCTION_BLUE" type="string" description="Transfer function for blue" />
  <Option name="TIFFTAG_TRANSFERRANGE_BLACK" type="string" description="Transfer range for black" />
  <Option name="TIFFTAG_TRANSFERRANGE_WHITE" type="string" description="Transfer range for white" />
  <Option name="STREAMABLE_OUTPUT" type="boolean" default="NO" description="Enforce a mode compatible with a streamable file" />
  <Option name="GEOTIFF_KEYS_FLAVOR" type="string-select" default="STANDARD" description="Which flavor of GeoTIFF keys must be used">
    <Value>STANDARD</Value>
    <Value>ESRI_PE</Value>
  </Option>
  <Option name="GEOTIFF_VERSION" type="string-select" default="AUTO" description="Which version of GeoTIFF must be used">
    <Value>AUTO</Value>
    <Value>1.0</Value>
    <Value>1.1</Value>
  </Option>
</CreationOptionList>

<OpenOptionList>
  <Option name="NUM_THREADS" type="string" description="Number of worker threads for compression. Can be set to ALL_CPUS" default="1" />
  <Option name="GEOTIFF_KEYS_FLAVOR" type="string-select" default="STANDARD" description="Which flavor of GeoTIFF keys must be used (for writing)">
    <Value>STANDARD</Value>
    <Value>ESRI_PE</Value>
  </Option>
  <Option name="GEOREF_SOURCES" type="string" description="Comma separated list made with values INTERNAL/TABFILE/WORLDFILE/PAM/NONE that describe the priority order for georeferencing" default="PAM,INTERNAL,TABFILE,WORLDFILE" />
  <Option name="SPARSE_OK" type="boolean" description="Should empty blocks be omitted on disk?" default="FALSE" />
</OpenOptionList>

  Other metadata items:
    LIBGEOTIFF=1700
    LIBTIFF=LIBTIFF, Version 4.1.0
Copyright (c) 1988-1996 Sam Leffler
Copyright (c) 1991-1996 Silicon Graphics, Inc.

From the list of create options above, it’s possible to determine the main GeoTIFF Driver’s writing capabilities:

• COMPRESS: customize the compression to be used when writing output data
• JPEG_QUALITY: specify a quality factor to be used by the JPEG compression
• TILED: When set to YES it allows to tiled output data
• BLOCKXSIZE, BLOCKYZISE: Specify the Tile dimension width and Tile dimension height
• PHOTOMETRIC: Specify the photometric interpretation of the data
• PROFILE: Specify the GeoTIFF profile to be used (some profiles only support a minimal set of TIFF Tags while some others provide a wider range of Tags)
• BIGTIFF: Specify when to write data as BigTIFF (A TIFF format which allows to break the 4GB Offset boundary)

gdalinfo - Getting Dataset/File Properties

The following instructions allow you to get information about the sample dataset previously configured in GeoServer

cd /opt/data/sample_data/user_data/aerial

gdalinfo 13tde815295_200803_0x6000m_cl.tif

Part of the gdalinfo output on a sample dataset.

• Block: It represents the internal tiling. Notice that the sample dataset has tiles made of 16 rows having width equals to the full image width.
• Overviews: It provides information about the underlying overviews. Notice that the sample dataset doesn’t have overviews since the Overviews property is totally missing from the gdalinfo output.

gdal_translate

This utility allows to convert a dataset to a different format by allowing a wide set of parameters to customize the conversion.

Running the command

gdal_translate

allows to get the list of supported parameters as well as the supported output formats

Usage: gdal_translate [--help-general]
       [-ot {Byte/Int16/UInt16/UInt32/Int32/Float32/Float64/
             CInt16/CInt32/CFloat32/CFloat64}] [-strict]
       [-of format] [-b band] [-mask band] [-expand {gray|rgb|rgba}]
       [-outsize xsize[%] ysize[%]]
       [- unscale] [-scale [src_min src_max [dst_min dst_max]]]
       [-srcwin xoff yoff xsize ysize] [-projwin ulx uly lrx lry]
       [-a_srs srs_def] [-a_ullr ulx uly lrx lry] [-a_nodata value]
       [-gcp pixel line easting northing [elevation]]*
       [-mo "META-TAG=VALUE"]* [-q] [-sds]
       [-co "NAME=VALUE"]* [-stats]
       src_dataset dst_dataset

The meaning of the main parameters is summarized below

• -ot: allows to specify the output datatype (Make sure that the specified datatype is contained in the Creation Datatypes list of the Writing driver)
• -of: specify the desired output format (GTIFF is the default value)
• -b: allows to specify an input band to be written in the output file. (Use multiple -b option to specify more bands)
• -mask: allows to specify an input band to be write an output dataset mask band.
• -expand: allows to expose a dataset with 1 band with a color table as a dataset with 3 (rgb) or 4 (rgba) bands. The (gray) value allows to expand a dataset with a color table containing only gray levels to a gray indexed dataset.
• -outsize: allows to set the size of the output file in terms of pixels and lines unless the % sign is attached in which case it’s as a fraction of the input image size.
• -unscale: allows to apply the scale/offset metadata for the bands to convert from scaled values to unscaled ones.
• -scale: allows to rescale the input pixels values from the range src_min to src_max to the range dst_min to dst_max. (If omitted the output range is 0 to 255. If omitted the input range is automatically computed from the source data).
• -srcwin: allows to select a subwindow from the source image in terms of xoffset, yoffset, width and height
• -projwin: allows to select a subwindow from the source image by specifying the corners given in georeferenced coordinates.
• -a_srs: allows to override the projection for the output file. The srs_def may be any of the usual GDAL/OGR forms, complete WKT, PROJ.4, EPSG:n or a file containing the WKT.
• -a_ullr: allows to assign/override the georeferenced bounds of the output file.
• -a_nodata: allows to assign a specified nodata value to output bands.
• -co: allows to set a creation option in the form “NAME=VALUE” to the output format driver. (Multiple -co options may be listed.)
• -stats: allows to get statistics (min, max, mean, stdDev) for each band
• src_dataset: is the source dataset name. It can be either file name, URL of data source or subdataset name for multi*-dataset files.
• dst_dataset: is the destination file name.

gdal_translate - Tiling the sample dataset

The following steps provide instructions to tile the sample dataset previously configured in GeoServer, by using the GeoTiff driver.

• Move to the parent folder /opt/data/sample_data/user_data

    cd /opt/data/sample_data/user_data
  

• Convert the input sample data to an output file having tiling set to 512x512 (the compression parameters are explained in).

    gdal_translate -co "TILED=YES" -co "BLOCKXSIZE=512" -co "BLOCKYSIZE=512"  -co "COMPRESS=JPEG" -co "PHOTOMETRIC=YCBCR" -co "QUALITY=85"  aerial/13tde815295_200803_0x6000m_cl.tif retiled/13tde815295_200803_0x6000m_cl.tif
  

• Check that the output dataset has successfully been tiled, by running the command

    gdalinfo retiled/13tde815295_200803_0x6000m_cl.tif
  

  

  Part of the gdalinfo output on the tiled dataset. Notice the Block value now is 512x512.

gdaladdo

This utility allows to add overviews to a dataset. The following steps provide instructions to add overviews to the tiled sample dataset.

Running the command

gdaladdo

allows to get the list of supported parameters

Usage: gdaladdo [-r {nearest,average,gauss,average_mp,average_magphase,mode}]
                [-ro] [--help-general] filename levels

The meaning of the main parameters is summarized below

• -r: allows to specify the resampling algorithm (Nearest is the default value)
• -ro: allows to open the dataset in read-only mode, in order to generate external overview (for GeoTIFF especially)
• filename: represents the file to build overviews for.
• levels: allows to specify a list of overview levels to build.

gdaladdo - Adding overviews to the sample dataset

• Move to the retiled folder

    cd retiled
  

• Run the gdaladdo command as follows

    gdaladdo -r average --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR --config JPEG_QUALITY_OVERVIEW 85 13tde815295_200803_0x6000m_cl.tif 2 4 8 16 32
  

• Check that the overviews have been added to the dataset, by running the command

    gdalinfo 13tde815295_200803_0x6000m_cl.tif
  

  

  Part of the gdalinfo output on the tiled dataset with overviews. Notice the Overviews properties.

Process in Bulk

Instead of manually repeating these 2 steps (retile + add overviews) for each file, we can invoke a few commands to get it automated.

cd /opt/data/sample_data/user_data/aerial

for i in `find *.tif`; do gdal_translate -CO "TILED=YES" -CO "BLOCKXSIZE=512" -CO "BLOCKYSIZE=512" -co "COMPRESS=JPEG" -co "PHOTOMETRIC=YCBCR" -co "QUALITY=85" $i ../optimized/$i; gdaladdo -r average --config COMPRESS_OVERVIEW JPEG --config PHOTOMETRIC_OVERVIEW YCBCR --config JPEG_QUALITY_OVERVIEW 85 ../optimized/$i 2 4 8 16 32; done

You should see a list of run like this

...
Input file size is 2500, 2500
0...10...20...30...40...50...60...70...80...90...100 - done.
0...10...20...30...40...50...60...70...80...90...100 - done.
Input file size is 2500, 2500
0...10...20...30...40...50...60...70...80...90...100 - done.
0...10...20...30...40...50...60...70...80...90...100 - done.
Input file size is 2500, 2500
0...10...20...30...40...50...60...70...80...90...100 - done.
0...10...20...30...40...50...60...70...80...90...100 - done.
...

At this point optimized datasets have been prepared and they are ready to be served by GeoServer as an ImageMosaic.

gdalwarp

This utility allows to warp and reproject a dataset. The following steps provide instructions to reproject the aerial dataset (which has EPSG:26913 coordinate reference system) to WGS84 (EPSG:4326).

Running the command

gdalwarp

allows to get the list of supported parameters

Usage: gdalwarp [--help-general] [--formats]
       [-s_srs srs_def] [-t_srs srs_def] [-to "NAME=VALUE"]
       [-order n | -tps | -rpc | -geoloc] [-et err_threshold]
       [-refine_gcps tolerance [minimum_gcps]]
       [-te xmin ymin xmax ymax] [-tr xres yres] [-tap] [-ts width height]
       [-wo "NAME=VALUE"] [-ot Byte/Int16/...] [-wt Byte/Int16]
       [-srcnodata "value [value...]"] [-dstnodata "value [value...]"] -dstalpha
       [-r resampling_method] [-wm memory_in_mb] [-multi] [-q]
       [-cutline datasource] [-cl layer] [-cwhere expression]
       [-csql statement] [-cblend dist_in_pixels] [-crop_to_cutline]
       [-of format] [-co "NAME=VALUE"]* [-overwrite]
       srcfile* dstfile

The meaning of the main parameters is summarized below

• -s_srs: allows to specify the source coordinate reference system
• -t_srs: allows to specify the target coordinate reference system
• -te: allows to set georeferenced extents (expressed in target CRS) of the output
• -tr: allows to specify the output resolution (expressed in target georeferenced units)
• -ts: allows to specify the output size in pixel and lines.
• -r: allows to specify the resampling method (one of near, bilinear, cubic, cubicspline and lanczos)
• -srcnodata: allows to specify band values to be excluded from interpolation.
• -dstnodata: allows to specify nodata values on output file.
• -wm: allows to specify the amount of memory (expressed in megabytes) used by the warping API for caching.

gdalwarp - Reprojecting sample dataset to WGS84

• Move to the /opt/data/sample_data/user_data/retiled folder

    cd /opt/data/sample_data/user_data/retiled
  

• Run the gdalwarp command

    gdalwarp -t_srs "EPSG:4326" -co "TILED=YES" 13tde815295_200803_0x6000m_cl.tif 13tde815295_200803_0x6000m_cl_warped.tif
  

• Check that reprojection has been successfull, by running the command

    gdalinfo 13tde815295_200803_0x6000m_cl_warped.tif
  

  

  Part of the gdalinfo output on the warped dataset. Notice the updated Coordinate System property.

Further Reading about GDAL

https://geoserver.geo-solutions.it/educational/en/raster_data/advanced_gdal/index.html

Publish the Optimized Mosaic on GeoNode

• Activate the geonode virtual env and move to /opt/geonode

• Run the updatelayers management command as follows

    ./manage_local.sh updatelayers --skip-geonode-registered -u test_user1 -w geonode -f boulder_bg_optimized
  

• Verify the new layer has been succesfully created on GeoNode

  

• Add the new layer to the Boulder map, and drag it to the bottom

  

Next Section: Optimizing, publishing and styling Vector data