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MODAPS Web Coverage Service (WCS) Quick Start Guide

1. MODAPS Web Coverage Service Locations
   • WCS Instances by Product
   • Service Endpoints
2. Workflow Synopsis
   • GetCapabilities
   • DescribeCoverage
   • GetCoverage
3. Additional Information
   • Coordinate Reference System
   • Axes and Bands
   • Resolution
4. Examples
   • Full Workflow
   • Sequential Days
   • Sample Code

Resource Locations

WCS Instances by Product

The WCS 1.0.0 specification does not provide an effective means to categorize and group coverages. MODAPS offers a large number of datasets and the response from a single GetCapabilities call would be very large.

We have provided a WCS instance for each data product in our catalogue.

Service Endpoints

The endpoint for the service varies based on product name and collection, and is of the form:

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/<collection>/<product>/getCapabilities

Some examples:

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/5/MOD03/getCapabilities?service=WCS&version=1.0.0&request=GetCapabilities

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/5/MOD021KM/getCapabilities?service=WCS&version=1.0.0&request=GetCapabilities

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/51/MOD06_L2/getCapabilities?service=WCS&version=1.0.0&request=GetCapabilities

Select the product and collection below to generate a GetCapabilities URL:

Collection:

Product:

Workflow Synopsis

GetCapabilities

Use this operation to get a list of coverages available for the product. The coverages are essentially the Science Data Sets (SDS) in the product, however there are some differences. For example the coverages are separated into Day and Night variations where applicable, and SDSs with fewer than 2 dimensions are excluded.

The GetCapabilities response is in XML format and will contain, among other things, a list of coverage names. Pass one of these coverage names to DescribeCoverage to get more detailed information about the coverage.

DescribeCoverage

This operation will return more specific details about a coverage, including the availability of data, available formats, etc. Provide a coverage name from the list obtained from GetCapabilities as the 'coverage' parameter.

GetCoverage

GetCoverage is called to make a data request. See the API for a list of required parameters, or below for some examples. After a period of processing which can last from 10 seconds to 10 minutes, the data will start to stream back to the client. Errors will be in XML format.

Additional Information

Coordinate Reference Systems

EPSG Codes

These codes define a projection along with a fixed value for relevant parameters. For example, EPSG:4326 ( Geographic ) and EPSG:20135 ( UTM Zone 35N ).

EPSG codes can be searched at http://www.epsg-registry.org/

AUTO2 codes

Another CRS type are AUTO2 codes, these are special CRS codes that allow variable values in the last two ( colon delimited ) fields. MODAPS WCS supports two AUTO2 codes:

urn:ogc:def:crs:OGC:1.3:AUTO2:42001:LAT:LON ( UTM )

urn:ogc:def:crs:OGC:1.3:AUTO2:42002:LAT:LON ( Transverse Mercator )

The LAT and LON portions in the above CRS codes should be substituted with the desired center latitude and center meridian (in decimal degrees).

CRS Usage in REST Interface

There are 2 parameters to GetCoverage that take CRS codes. The "crs" parameter indicates the CRS used in defining your "bbox" parameter. For MODAPS WCS this must always be "EPSG:4326" ( Geographic ).

The "response_crs" parameter is where you use a CRS code (either EPSG or AUTO2) to specify the projection of the output file you are requesting.

Axes and Bands

If a coverage has three or more dimensions ( e.g. a list of bands ), the DescribeCoverage response will contain a RangeSubset section with a list of AxisDescriptions. The Name field in the AxisDescription is the name of the 3rd ( or sometimes 4th ) dimension. Also present is a range of valid values.

If this section is present, you must provide a value for these axes. In the REST interface, the syntax is: axis_name=N/N/1 where axis_name is the name from the DescribeCoverage response, and N is the slice you would like.

For example, The coverage EV_1KM_Emissive from the product MOD021KM, has a 3rd dimension representing band. The DescribeCoverage response for EV_1KM_Emissive shows the name of the 3rd axes to be Band_1KM_Emissive, with valid values ranging from 1 to 16. So in GetCoverage you would use Band_1KM_Emissive=7/7/1 for band 7, or Band_1KM_Emissive=3/3/1 for band 3. Currently only one band per request is supported.

Resolution

Examples

Full Workflow

1) Get a list of coverages for product MOD021KM, collection 5:

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/5/MOD021KM/getCapabilities?service=WCS&version=1.0.0&request=GetCapabilities

2) Get more information for coverage EV_1KM_Emissive_Uncert_Indexes:Day

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/5/MOD021KM/describeCoverage?service=WCS&version=1.0.0&request=DescribeCoverage&coverage=EV_1KM_Emissive_Uncert_Indexes:Day

3) Request data for 2010-10-21, bbox -80,35,-75,40, in HDF4 format, Geographic projection:

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/5/MOD021KM/getCoverage?service=WCS&version=1.0.0&request=GetCoverage&coverage=EV_1KM_Emissive_Uncert_Indexes:Day&bbox=-80,35,-75,40&time=2010-10-21T00:00:00&format=hdf4&response_crs=EPSG:4326&Band_1KM_Emissive=1/1/1

Get a coverage for 3 sequential days, in geotiff format

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/5/MOD021KM/getCoverage?service=WCS&version=1.0.0&request=GetCoverage&coverage=EV_1KM_Emissive_Uncert_Indexes:Day&bbox=-80,35,-75,40&time=2010-10-21T00:00:00&format=geotiff&response_crs=EPSG:4326&Band_1KM_Emissive=1/1/1

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/5/MOD021KM/getCoverage?service=WCS&version=1.0.0&request=GetCoverage&coverage=EV_1KM_Emissive_Uncert_Indexes:Day&bbox=-80,35,-75,40&time=2010-10-22T00:00:00&format=geotiff&response_crs=EPSG:4326&Band_1KM_Emissive=1/1/1

http://modwebsrv.modaps.eosdis.nasa.gov/wcs/5/MOD021KM/getCoverage?service=WCS&version=1.0.0&request=GetCoverage&coverage=EV_1KM_Emissive_Uncert_Indexes:Day&bbox=-80,35,-75,40&time=2010-10-23T00:00:00&format=geotiff&response_crs=EPSG:4326&Band_1KM_Emissive=1/1/1

Example XML Requests

GetCapabilities

DescribeCoverage

GetCoverage

Code Examples

Coming soon.

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