Working with Data¶
Where to Find Data¶
Help us add useful sources of Free data to this list.
- ReadyMap.org - Free 15m imagery, elevation, and street tiles for osgEarth developers
- USGS National Map - Elevation, orthoimagery, hydrography, geographic names, boundaries, transportation, structures, and land cover products for the US.
- NASA BlueMarble - NASA’s whole-earth imagery (including topography and bathymetry maps)
- Natural Earth - Free vector and raster map data at various scales
- Virtual Terrain Project - Various sources for whole-earth imagery
- Bing Maps - Microsoft’s worldwide imagery and map data ($)
Tips for Preparing your own Data¶
Processing Local Source Data
If you have geospatial data that you would like to view in osgEarth, you can usually use the GDAL driver. If you plan on doing this, try loading it as-is first. If you find that it’s too slow, here are some tips for optimizing your data for tiled access.
Reproject your data
osgEarth will reproject your data on-the-fly if it does not have the necessary coordinate system. For instance, if you are trying to view a UTM image on a geodetic globe (epsg:4326). However, osgEarth will run much faster if your data is already in the correct coordinate system. You can use any tool you want to reproject your data such as GDAL, Global Mapper or ArcGIS.
For example, to reproject a UTM image to geodetic using gdal_warp:gdalwarp -t_srs epsg:4326 my_utm_image.tif my_gd_image.tif
Build internal tiles
Typically formats such as GeoTiff store their pixel data in scanlines. However, using a tiled dataset will be more efficient for osgEarth because of how it uses tiles internally.
To create a tiled GeoTiff using gdal_translate, issue the following command:gdal_translate -of GTiff -co TILED=YES input.tif output.tif
Take is a step further and use compression to save space. You can use internal JPEG compression if your data contains no transparency:gdal_translate -of GTiff -co TILED=YES -co COMPRESS=JPG input.tif output.tif
Adding overviews (also called ‘’pyramids’’ or ‘’rsets’‘) can sometimes increase the performance of a large data source in osgEarth. You can use the gdaladdo utility to add overviews to a dataset:gdaladdo -r average myimage.tif 2 4 8 16
Building tile sets with osgearth_conv
Pre-tiling your imagery can speed up load time dramatically, especially over the network. In fact, if you want to serve your data over the network, this is the only way!
osgearth_conv is a low-level conversion tool that comes with osgEarth. One useful application of the tool is tile up a large GeoTIFF (or other input) in a tiled format. Note: this approach only works with drivers that support writing (MBTiles, TMS).
To make a portable MBTiles file:osgearth_conv --in driver gdal --in url myLargeFile.tif --out driver mbtiles --out filename myData.mbtiles --out format jpg
If you want to serve tiles from a web server, use TMS:osgearth_conv --in driver gdal --in url myLargeData.tif --out driver tms --out url myLargeData/tms.xml --out format jpg
That will yield a folder (called “myLargeData” in this case) that you can deploy on the web behind any standard web server (e.g. Apache).
Tip: If you are tiling elevation data, you will need to add the
jpgformat does NOT support transparency. If your data was an alpha channel, use
Just type osgearth_conv for a full list of options. The
--outoptions correspond directly to properties you would normally include in an Earth file.
Building tile sets with the packager
Another way to speed up imagery and elevation loading in osgEarth is to build tile sets.
This process takes the source data and chops it up into a quad-tree hierarchy of discrete tiles that osgEarth can load very quickly. Normally, if you load a GeoTIFF (for example), osgEarth has to create the tiles at runtime in order to build the globe; Doing this beforehand means less work for osgEarth when you run your application.
osgearth_package is a utility that prepares source data for use in osgEarth. It is optional - you can run osgEarth against your raw source data and it will work fine - but you can use osgearth_package to build optimized tile sets that will maximize performance in most cases. Usage:osgearth_package file.earth --tms --out output_folder
This will load each of the data sources in the earth file (
file.earthin this case) and generate a TMS repository for each under the folder
output_folder. You can also specify options:
--out path Root output folder of the TMS repo --ext extension Output file extension --max-level level Maximum level of detail
–bounds xmin ymin xmax ymax Bounds to package (in map coordinates; default=entire map) –out-earth Generate an output earth file referencing the new repo –overwrite Force overwriting of existing files –keep-empties Writes fully transparent image tiles (normally discarded) –db-options An optional OSG options string –verbose Displays progress of the operation
Spatial indexing for feature data
Large vector feature datasets (e.g., shapefiles) will benefit greatly from a spatial index. Using the ogrinfo tool (included with GDAL/OGR binary distributions) you can create a spatial index for your vector data like so:ogrinfo -sql "CREATE SPATIAL INDEX ON myfile" myfile.shp
For shapefiles, this will generate a “.qix” file that contains the spatial index information.