Processing Data For Serving

From OpenAerialMap

OpenAerialMap has the ability to load data from a remote WMS server. The ideal WMS server is one which is fast, and serves data directly in EPSG:4326 (geographic/lat lon unprojected). In order to serve data in this projection, some work must be done on the data provider's side. This page describes, given a set of images and a Linux machine, how to serve your images out as a fast WMS service.

1. Download FWTools. http://home.gdal.org/fwtools/FWTools-linux-2.0.0.tar.gz
2. Unpack, and run the installer script in the root of the FWTools directory.
3. Find a disk with lots of space. If your source data is stored in MrSID or JPEG2000, your resulting uncompressed data will be anywhere from 10-30 times larger.
4. Extract and warp your imagery. Something like this will need to be run for each file:

 bin_safe/gdalwarp --config GDAL_CACHEMAX 300 -wm 300 -t_srs EPSG:4326 -of GTiff -co TILED=yes 
   -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 /my/input/directory/source_image1.sid /my/output/directory/output_image1.tiff

1. If your images are decompressed from a lossy compression format, you will want to run the nearblack utility on them to remove collars:

 bin_safe/nearblack -nb 5 /my/output/directory/output_image1.tiff

1. Add overviews to the image:

 bin_safe/gdaladdo --config GDAL_CACHEMAX 300 /my/output/directory/output_image1.tiff 2 4 8 16 32 64 128 256

1. Once you have done this for all the images in the directory, you will want to build a tileindex against the output images:

 bin_safe/gdaltindex /my/output/directory/index.shp `find /my/output/directory/ -name \*.tiff`

1. Next, you'll want to set up a mapfile for the data:

MAP
 EXTENT -180 -90 180 90
 IMAGECOLOR 0 0 0 
 IMAGETYPE jpeg
 SIZE 256 256 
 STATUS ON
 UNITS DD
 NAME "World"

 OUTPUTFORMAT
   NAME jpeg
   MIMETYPE image/jpeg
   DRIVER GD/JPEG
   EXTENSION jpeg
   TRANSPARENT FALSE
 END

 PROJECTION
   "init=epsg:4326"
 END

 WEB
   IMAGEPATH "/tmp/"
   IMAGEURL "/tmp/"
     METADATA
       "original_projection" "init=epsg:4326"
       "original_extents"  "-180,-90,180,90"
       "wms_srs" "EPSG:4326"
     END
 END
 layer
     name  "orthos"
     type raster
     status on
     tileindex "/my/output/directory/index.shp"
     projection "init=epsg:4326" end
     OFFSITE 0 0 0  
     METADATA
       "wms_title" "2006 Massachusetts Orthos"
       "wms_abstract" "2006 NAIP photos, releaesd into the public domain. "
       "wms_attribution_title" "USDA"
       "wms_attribution_onlineresource" "http://www.example.com/my/metadata/link/"
     END
 END
END

Save this file into /my/output/directory/orthos.map

1. Finally, symlink from /usr/lib/cgi-bin/my_orthos to /your/fwtools/home/bin_safe/mapserv (cgi-bin location is specific to your setup -- this part needs more work, need to mention some apache config)
2. Lastly, visit http://your.wms.server/cgi-bin/my_orthos?map=/my/output/directory/orthos.map&service=WMS&request=GetCapabilities