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Using griddap to Request Data and Graphs from Gridded Datasets

The URL specifies what you want: the dataset, a description of the graph or the subset of the data, and the file
type for the response.

• (easy) You can get data by using the dataset's Data Access Form. It makes the URL for you.
• (easy) You can make a graph or map by using the dataset's Make A Graph form. It makes the URL for you.
• (not hard) You can bypass the forms and get the data or make a graph or map by generating the URL by
  hand or with a computer program or script.

griddap request URLs must be in the form
   http://edac-dap2.northerngulfinstitute.org/erddap/griddap/datasetID.fileType{?query}
For example,
   http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?sst[(2007-10-21T00:00:00)][0][(-75):100:(75)][(180):100:(360)]
Thus, the query is often a variable name (e.g., sst),
followed by a set of [] for each of the variable's dimensions
(for example, [time][altitude][latitude][longitude]),
with your desired (start):stride:(stop) values within each [].

Details:

• Requests must not have any internal spaces.
• Requests are case sensitive.
• {} is notation to denote an optional part of the request.
   
• datasetID identifies the name that ERDDAP assigned to the dataset (for example, erdBAssta5day).
  You can see a list of datasetID options available via griddap.
   
• fileType specifies the type of grid data file that you want to download (for example, .htmlTable).
  The actual extension of the resulting file may be slightly different than the fileType (for example,
  .smallPdf returns a small .pdf file).
  The fileType options for downloading gridded data are:
   

  Data fileTypes	Description	Info	Example
  .asc	View OPeNDAP-style comma-separated ASCII text.	info	example
  .csv	Download a comma-separated ASCII text table (line 1: names; line 2: units; ISO 8601 times).	info	example
  .csvp	Download a .csv file with line 1: name (units). Times are ISO 8601 strings.	info	example
  .das	View the data's metadata via an OPeNDAP Dataset Attribute Structure (DAS).	info	example
  .dds	View the data's structure via an OPeNDAP Dataset Descriptor Structure (DDS).	info	example
  .dods	OPeNDAP clients use this to download the data in the DODS binary format.	info	example
  .esriAscii	Download an ESRI ASCII file (for lat lon data only; lon must be all below or all above 180).	info	example
  .graph	View a Make A Graph web page.	info	example
  .help	View a web page with a description of griddap.	info	example
  .html	View an OPeNDAP-style HTML Data Access Form.	info	example
  .htmlTable	View a .html web page with the data in a table. Times are ISO 8601 strings.	info	example
  .json	View a JSON table (missing value = 'null'; times are ISO 8601 strings).	info	example
  .mat	Download a MATLAB binary file.	info	example
  .nc	Download a NetCDF binary file with COARDS/CF/THREDDS metadata.	info	example
  .ncHeader	View the header (the metadata) for the NetCDF file.	info	example
  .odvTxt	Download time,latitude,longitude,otherVariables as an ODV Generic Spreadsheet File (.txt).	info	example
  .tsv	Download a tab-separated ASCII text table (line 1: names; line 2: units; ISO 8601 times).	info	example
  .tsvp	Download a .tsv file with line 1: name (units). Times are ISO 8601 strings.	info	example
  .xhtml	View an XHTML (XML) file with the data in a table. Times are ISO 8601 strings.	info	example

  
  For example, here is a request to download data formatted as an HTML table:
  http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?sst[(2007-10-21T00:00:00)][0][(-75):100:(75)][(180):100:(360)]

  ArcGIS is a family of Geographical Information Systems (GIS) products from ESRI:
  ArcView, ArcEditor, and ArcInfo. To get data from ERDDAP into your ArcGIS program:
  in ERDDAP, save some data in an .esriAscii file. The file's extension will be .asc.
  Then, import the data file into your ArcGIS program:

  • For ArcInfo v8 or higher:
    1. Open ArcInfo.
    2. Use ArcToolbox.
    3. Use the Import to Raster : ASCII to Grid command
  • For ArcView's or ArcEditor's ArcMap:
    1. Open ArcMap.
    2. Choose a new empty map or load an existing map.
    3. Click on the ArcToolbox icon.
       1. Open Conversion Tools : To Raster : ASCII to Raster
          1. Input Raster File - Browse to select the .esriAscii .asc file.
          2. Output Raster File - Keep the default (or change it).
          3. Output Data Type - change to FLOAT.
          4. Click on OK.
       2. Open Data Management Tools : Projections and Transformations : Define Projection
          1. Input Dataset or Feature Class - Browse to select the Raster (GRID) that was just
             created (on disk).
          2. Coordinate System - click the icon to the right of the text box.
             That will open the Spatial Reference Properties window.
             1. Click the Select button.
             2. Choose the Geographic Coordinate Systems folder. (Most data in ERDDAP uses a
                'geographic' projection, otherwise known as unprojected data or lat/lon data).
             3. Select on the Spheroid-based folder.
             4. Select the Clarke 1866.prj file and click Add.
             5. Click OK in the Spatial Reference Properties Window.
             6. Click OK in the Define Projection Window.
  • For older ArcView (v3) - You need the Spatial Analyst extension, which is sold separately.
    1. Open ArcView
    2. Open Spatial Analyst
    3. Use Import Data Source : ASCII Raster

  Shapefiles - We do not distribute grid data as shapefiles because shapefiles are usually
  an inappropriate file format for distributing grid data. If the grid data is stored in a
  shapefile, it is either treated as sets of points (MultiPointM or MultiPoint objects,
  where one loses the information that the points are arranged in a grid) or as a Polygons
  (where one deals with contiguous areas with a specific range of values, for example,
  16 degrees <= Temperature < 17 degrees, where one loses the actual data values and the
  information that the points are arranged in a grid). Such shapefiles can and should be
  derived from the original grid data, which we do distribute.

  We believe that the ESRI .asc files available from ERDDAP are the appropriate form for
  distributing grid data to the ArcGIS programs. In fact, this ESRI .asc format was designed
  by ESRI for this exact purpose -- the transfer of grid data between computers.

  JSONP - Requests for .json files may now include an optional jsonp request
  by adding &.jsonp=functionName to the end of the query.
  Basically, this just tells ERDDAP to add functionName( to the beginning of the
  response and ")" to the end of the response.
  If originally there was no query, leave off the "&" in your query.

  MATLAB users can use griddap's .mat file type to download data from within MATLAB.
  Here is a one line example:

  load(urlwrite('http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.mat?sst[(2007-10-21)][0][(-75):50:(75)][(180):50:(360)]&.draw=surface&.vars=longitude|latitude|sst&.colorBar=Rainbow|C|Linear|0|32|', 'test.mat'));

  The data will be in a MATLAB structure. The structure's name will be the datasetID
  (for example, erdBAssta5day).
  The structure's internal variables will have the same names as in ERDDAP,
  (for example, use fieldnames(erdBAssta5day)).
  If you download a 2D matrix of data (as in the example above), you can plot it with
  (for example):

  imagesc(erdBAssta5day.longitude, erdBAssta5day.latitude, squeeze(erdBAssta5day.sst), [0 32])
  set(gca, 'YDir', 'normal')

  The numbers at the end of the first line specify the range for the color mapping.
  The 'set' command flips the map to make it upright.

  Ocean Data View (ODV) users can download data in the ODV Generic Spreadsheet Format
  .txt file by requesting griddap's .odvTxt fileType.
  The dataset MUST include longitude, latitude, and time dimensions.
  Any longitude vales are fine.
  After saving the resulting file (with the extension .txt) in your computer:

  1. Open ODV.
  2. Use File : Open.
     • Change Files of type to Data Files (*.txt *.csv *.jos *.o4x).
     • Browse to select the .txt file you created in ERDDAP and click on Open.
       The data locations should now be visible on a map in ODV.
  3. If you downloaded a longitude, latitude slice of a dataset, use:
     • Press F12 or View : Layout Templates : 1 SURFACE Window to view the default isosurface variable.
     • If you want to view a different isosurface variable,
       • To define a new isosurface variable, use View : Isosurface Variables.
       • Right click on the map and choose Properties : Data : Z-axis to pick
         the new isosurface variable.
  4. See ODV's Help menu for more help using ODV.

  Making an Image File with a Graph or Map of Gridded Data
  If a griddap request URL specifies a subset of data which is suitable for making
  a graph or a map, and the fileType is an image fileType, griddap will return an image
  with a graph or map.
  griddap request URLs can include optional graphics commands which let you
  customize the graph or map.
  As with other griddap request URLs, you can create these URLs by hand or have a
  computer program do it. Or, you can use the Make A Graph web pages, which simplify
  creating these URLs (see the "graph" links in the table of griddap datasets).

  The fileType options for downloading images of graphs and maps of grid data are:

  Image fileTypes	Description	Info	Example
  .geotif	View a GeoTIFF .tif image file (for lat lon data only; lon must be all below or all above 180).	info	example
  .kml	View a Google Earth .kml file (for lat, lon, [time] results only)	info	example
  .smallPdf	View a small .pdf image file with a graph or map.	info	example
  .pdf	View a standard, medium-sized, .pdf image file with a graph or map.	info	example
  .largePdf	View a large .pdf image file with a graph or map.	info	example
  .smallPng	View a small .png image file with a graph or map.	info	example
  .png	View a standard, medium-sized .png image file with a graph or map.	info	example
  .largePng	View a large .png image file with a graph or map.	info	example
  .transparentPng	View a .png image file (a geographic map without axes, landmask, or legend).	info	example

  The .transparentPng option will make a geographic map without axes, landmask,
  or legend, and with a transparent (not opaque white) background.
  This option can't be used for other types of graphs, for example, line graghs.
  The .transparentPng image doesn't have a standard size. Instead, it makes an
  image where one data point becomes one pixel. So in most cases, you should use
  a stride value (see below) for the latitude and longitude axes, or use the
  &.size=width|height parameter to restrict the image size, so that the image isn't *huge*.

  Incompatibilities
  Some results file types have restrictions. For example, Google Earth .kml is only
  appropriate for results with longitude and latitude values. If a given request is
  incompatible with the requested file type, griddap throws an error.
   

• query is the part of the request after the "?".
  It specifies the subset of data that you want to receive.
  In griddap, it is an optional OPeNDAP DAP-style hyperslab query which can request:
  • One or more dimension (axis) variables, for example
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?latitude[0:10:100] .
  • One or more data variables, for example
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?sst[656][0][0:100:1500][1800:100:3600] .
    To request more than one data variable, separate the desired data variable names by commas.
    If you do request more than one data variable, the requested subset for each variable
    must be identical (see below).
    (In griddap, all data variables within a grid dataset share the same dimensions.)
  • The entire dataset. Omitting the entire query is the same as requesting all of the data
    for all of the variables. Because of the large size of most datasets, this is usually
    only appropriate for fileTypes that return information about the dataset (for example,
    .das, .dds, and .html), but don't return all of the actual data values. For example,
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.dds
    griddap is designed to handle requests of any size but trying to download all of the
    data with one request will usually fail (for example, downloads that last days usually
    fail at some point). If you need all of the data, consider breaking your big request
    into several smaller requests. If you just need a sample of the data, use the largest
    acceptable stride values (see below) to minimize the download time.

  Using [start:stride:stop]
  When requesting dimension (axis) variables or data variables, the query may
  specify a subset of a given dimension by identifying the [start{{:stride}:stop}]
  indices for that dimension.

  • start is the index of the first desired value. Indices are 0-based.
    (0 is the first index. 1 is the second index. ...)
  • stride indicates how many intervening values to get: 1=get every value,
    2=get every other value, 3=get every third value, ...
    Stride values are in index units (not the units of the dimension).
  • stop is the index of the last desired value.
  • Specifying only two values for a dimension (i.e., [start:stop]) is interpreted
    as [start:1:stop].
  • Specifying only one value for a dimension (i.e., [start]) is interpreted
    as [start:1:start].
  • Specifying no values for a dimension (i.e., []) is interpreted as [0:1:max].
  • Omitting all of the [start:stride:stop] values (that is, requesting the
    variable without the subset constraint) is equivalent to requesting the entire variable.
    For dimension variables (for example, longitude, latitude, and time) and for fileTypes
    that don't download actual data (notably, .das, .dds, .html, and all of the graph and
    map fileTypes) this is fine. For example,
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.dds?sst
    For data variables, the resulting data may be very large.
    griddap is designed to handle requests of any size. But if you try to download all of
    the data with one request, the request will often fail for other reasons (for example,
    downloads that last for days usually fail at some point). If you need all of the data,
    consider breaking your big request into several smaller requests.
    If you just need a sample of the data, use the largest acceptable stride values
    to minimize the download time.
  • last - ERDDAP extends the OPeNDAP standard by interpreting
    a start or stop value of last as the last available index value.
    You can also use the notation last-n (e.g., last-10)
    to specify the last index minus some number of indices.
    You can use '+' in place of '-'. The number of indices can be negative.
  • griddap extends the standard OPeNDAP subset syntax by allowing the start
    and/or stop values to be actual dimension values (for example, longitude values
    in degrees_east) within parentheses, instead of array indices.
    This example with [time][altitude][latitude][longitude] dimension values
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?sst[(1192924800)][0][(-75):100:(75)][(180):100:(360)]
    is (at least at the time of writing this) equivalent to this example with dimension indices
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?sst[656][0][0:100:1500][1800:100:3600]
    The value in parentheses must be within the range of values for the dimension.
    If the value in parentheses doesn't exactly equal one of the dimension values, the
    closest dimension value will be used.
  • griddap does not allow parentheses around stride values.
    The reasoning is: With the start and stop values, it is easy to convert the value in
    parentheses into the appropriate index value by finding the nearest dimension value.
    This works if the dimension values are evenly spaced or not.
    If the dimension values were always evenly spaced, it would be easy to use a similar
    technique to convert a stride value in parentheses into a stride index value.
    But dimension values often aren't evenly spaced. So for now, ERDDAP doesn't support the
    parentheses notation for stride values.
  • griddap always stores date/time values as numbers (in seconds since 1970-01-01T00:00:00Z).
    Here is an example of a query which includes date/time numbers:
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?sst[(1192924800)][0][(-75):100:(75)][(180):100:(360)]
    Some fileTypes (notably, .csv, .tsv, .htmlTable, .odvTxt, and .xhtml) display date/time values as
    ISO 8601:2004 "extended" date/time strings (e.g., 2002-08-03T12:30:00Z).
  • For the time dimension, griddap extends the OPeNDAP standard by allowing you to specify an
    ISO 8601 date/time values in parentheses, which griddap then converts to the internal
    number (in seconds since 1970-01-01T00:00:00Z) and then to the appropriate array index.
    The ISO date/time value should be in the form: YYYY-MM-DDThh:mm:ssZ, where Z is 'Z'
    or a ±hh:mm offset from UTC.
    If you omit Z (or the ±hh:mm offset), :ssZ, :mm:ssZ, or Thh:mm:ssZ from the ISO date/time
    that you specify, the missing fields are assumed to be 0.
    The example below is equivalent (at least at the time of writing this) to the examples above:
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?sst[(2007-10-21T00:00:00)][0][(-75):100:(75)][(180):100:(360)]
  • (last) - ERDDAP interprets a start or stop value of (last) as the last
    available index.
    You can also use the notation (last-d) (e.g., last-10.5) to specify
    the last index's value minus some number, which is then converted to the nearest
    index. You can use '+' in place of '-'. The number can be negative.
    For a time axis, the number is interpreted as some number of seconds.
  • Graphics Commands - griddap extends the OPeNDAP standard by allowing graphics commands
    in the query.
    The Make A Graph web pages simplify the creation of URLs with these graphics commands
    (see the "graph" links in the table of griddap datasets).
    So we recommend using the Make A Graph web pages to generate URLs, and then, when
    needed, using the information here to modify the URLs for special purposes.
    These commands are optional.
    If present, they must occur after the data request part of the query.
    These commands are used by griddap if you request an image fileType (PNG or PDF) and are
    ignored if you request a data file (e.g., .asc).
    If relevant commands are not included in your request, griddap uses the defaults and tries
    its best to generate a reasonable graph or map.
    All of the commands are in the form &.commandName=value .
    If the value has sub-values, they are separated by the '|' character.
    The commands are:
    • &.colorBar=palette|continuous|scale|min|max|nSections
      This specifies the settings for a color bar. The sub-values are:
      • palette - All ERDDAP installations support a standard set of palettes:
        BlackBlueWhite, BlackRedWhite, BlackWhite, BlueWhiteRed, LightRainbow,
        Ocean, Rainbow, RedWhiteBlue, ReverseRainbow, Topography, WhiteBlack,
        WhiteBlueBlack, WhiteRedBlack.
        Some ERDDAP installations support additional options. See a Make A Graph
        web page for a complete list.
        The default varies based on min and max: if -1*min ~= max, the default
        is BlueWhiteRed; otherwise, the default is Rainbow.
      • continuous - must be either no value (the default), 'C' (for Continuous),
        or 'D' (for Discrete). The default is different for different datasets.
      • scale - must be either no value (the default), Linear, or Log.
        The default is different for different datasets.
      • min - The minimum value for the color bar.
        The default is different for different datasets.
      • max - The maximum value for the color bar.
        The default is different for different datasets.
      • nSections - The preferred number of sections (for Log color bars,
        this is a minimum value). The default is different for different datasets.
      If you don't specify one of the sub-values, the default for the sub-value will be used.
    • &.color=value
      This specifies the color for data lines, markers, vectors, etc. The value must
      be specified as an 0xRRGGBB value (e.g., 0xFF0000 is red, 0x00FF00 is green).
      The default is 0x000000 (black).
    • &.draw=value
      This specifies how the data will be drawn, as lines, linesAndMarkers,
      markers, sticks, surface, or vectors.
    • &.font=scaleFactor
      This specifies a scale factor for the font (e.g., 1.5 would make the font
      1.5 times as big as normal).
    • &.land=value
      This specifies whether the landmask should be drawn under or over the data.
      The default is different for different datasets (under the ERDDAP administrator's
      control via a drawLandMask setting in datasets.xml, or via the fallback drawLandMask
      setting in setup.xml).
      Terrestrial researchers usually prefer under.
      Oceanographers often prefer over.
    • &.legend=value
      This specifies whether the legend on PNG images (not PDF's) should be at the
      Bottom (default), Off, or Only (which returns only the legend).
    • &.marker=markerType|markerSize
      markerType is an integer: 0=None, 1=Plus, 2=X, 3=Dot, 4=Square,
      5=Filled Square (default), 6=Circle, 7=Filled Circle, 8=Up Triangle,
      9=Filled Up Triangle.
      markerSize is an integer from 3 to 50 (default=5)
    • &.size=width|height
      For PNG images (not PDF's), this specifies the desired size of the image, in pixels.
      This allows you to specify sizes other than the predefined sizes of .smallPng, .png,
      and .largePng, or the variable size of .transparentPng.
    • &.trim=trimPixels
      For PNG images (not PDF's), this tells ERDDAP to make the image shorter by removing
      all whitespace at the bottom, except for trimPixels.
    • &.vars='|'-separated list
      This is a '|'-separated list of variables names. Defaults are hard to predict.
      The meaning associated with each position varies with the &.draw value:
      • for lines: xAxis|yAxis
      • for linesAndMarkers: xAxis|yAxis|Color
      • for markers: xAxis|yAxis|Color
      • for sticks: xAxis|uComponent|vComponent
      • for surface: xAxis|yAxis|Color
      • for vectors: xAxis|yAxis|uComponent|vComponent
      If xAxis=longitude and yAxis=latitude, you get a map; otherwise, you get a graph.
    • &.vec=value
      This specifies the data vector length (in data units) to be scaled to the
      size of the sample vector in the legend. The default varies based on the data.
    • &.xRange=min|max
      This specifies the min|max for the X axis. The default varies based on the data.
    • &.yRange=min|max
      This specifies the min|max for the Y axis. The default varies based on the data.
    
    A sample graph URL is
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.png?sst[(2007-07-01):(2007-10-21)][0][(29)][(225)]&.draw=linesAndMarkers&.vars=time|sst|&.marker=1|3&.color=0xFF9900&.colorBar=|C|Linear|||

    Or, if you change the fileType in the URL from .png to .graph, you can see a Make A Graph
    web page with that request loaded:
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.graph?sst[(2007-07-01):(2007-10-21)][0][(29)][(225)]&.draw=linesAndMarkers&.vars=time|sst|&.marker=1|3&.color=0xFF9900&.colorBar=|C|Linear|||
    That makes it easy for humans to modify an image request to make a similar graph or map.

    Or, if you change the fileType in the URL from .png to a data fileType (e.g., .htmlTable), you can download the data that was graphed:
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?sst[(2007-07-01):(2007-10-21)][0][(29)][(225)]&.draw=linesAndMarkers&.vars=time|sst|&.marker=1|3&.color=0xFF9900&.colorBar=|C|Linear|||

    A sample map URL is
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.png?sst[(2007-10-21)][0][(-75):50:(75)][(180):50:(360)]&.draw=surface&.vars=longitude|latitude|sst&.colorBar=Rainbow|C|Linear|0|32|

    Or, if you change the fileType in the URL from .png to .graph, you can see a Make A Graph
    web page with that request loaded:
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.graph?sst[(2007-10-21)][0][(-75):50:(75)][(180):50:(360)]&.draw=surface&.vars=longitude|latitude|sst&.colorBar=Rainbow|C|Linear|0|32|

    Or, if you change the fileType in the URL from .png to a data fileType (e.g., .htmlTable),
    you can download the data that was mapped:
    http://edac-dap2.northerngulfinstitute.org/erddap/griddap/erdBAssta5day.htmlTable?sst[(2007-10-21)][0][(-75):50:(75)][(180):50:(360)]&.draw=surface&.vars=longitude|latitude|sst&.colorBar=Rainbow|C|Linear|0|32|

• Data Model - Each griddap dataset can be represented as:
  • An ordered list of one or more 1-dimensional axis variables.
    Each axis variable has data of one specific type.
    If the data source has a dimension with a size but no values, ERDDAP uses the values
    0, 1, 2, ...
    The supported types are int8, uint16, int16, int32, int64, float32, and float64.
    Missing values are not allowed.
    The values MUST be sorted in either ascending (recommended) or descending order.
    Unsorted values are not allowed because [(start):(stop)] requests must
    translate into a contiguous range of indices.
    Tied values are not allowed because requests for a single [(value)] must
    translate unambiguously to one index.
    Each axis variable has a name composed of a letter (A-Z, a-z) and then 0 or more
    characters (A-Z, a-z, 0-9, _).
    Each axis variable has metadata which is a set of Key=Value pairs.
  • A set of one or more n-dimensional data variables.
    All data variables use all of the axis variables, in order, as their dimensions.
    Each data variable has data of one specific type.
    The supported types are (int8, uint16, int16, int32, int64, float32, float64, and
    String of any length).
    Missing values are allowed.
    Each data variable has a name composed of a letter (A-Z, a-z) and then 0
    or more characters (A-Z, a-z, 0-9, _).
    Each data variable has metadata which is a set of Key=Value pairs.
  • The dataset has Global metadata which is a set of Key=Value pairs.
  • Note about metadata: each variable's metadata and the global metadata is a set of 0
    or more Key=Value pairs.
    Each Key is a String consisting of a letter (A-Z, a-z) and then 0 or more other
    characters (A-Z, a-z, 0-9, '_').
    Each Value is either one or more numbers (of one Java type), or one or more Strings
    of any length (using \n as the separator).
     
• Special Variables
  • In griddap, a longitude axis variable (if present) always has the name "longitude"
    and the units "degrees_east".
  • In griddap, a latitude axis variable (if present) always has the name, "latitude"
    and the units "degrees_north".
  • In griddap, an altitude axis variable (if present) always has the name "altitude"
    and the units "m" above sea level.
    Locations below sea level have negative altitude values.
  • In griddap, a time axis variable (if present) always has the name "time"
    and the units "seconds since 1970-01-01T00:00:00Z".
    If you request data and specify a start and/or stop value for the time axis,
    you can specify the time as a number (in seconds since 1970-01-01T00:00:00Z)
    or as a String value (e.g., "2002-12-25T07:00:00Z" in the GMT/Zulu time zone).
  • Because the longitude, latitude, altitude, and time axis variables are specifically
    recognized, ERDDAP is aware of the spatiotemporal features of each dataset.
    This is useful when making images with maps or time-series, and when saving data
    in geo-referenced file types (e.g., .esriAscii and .kml).
     
• Incompatibilities
  • File Types - Some results file types have restrictions.
    For example, .kml is only appropriate for results with a range of longitude and
    latitude values.
    If a given request is incompatible with the requested file type, griddap throws an error.
     
• Requesting Compressed Files
  ERDDAP doesn't offer results stored in compressed (e.g., .zip or .gzip) files.
  Instead, ERDDAP looks for accept-encoding in the HTTP GET request header sent
  by the client. If a supported compression type ("gzip", "x-gzip", or "deflate") is found
  in the accept-encoding list, ERDDAP includes "content-encoding" in the HTTP response
  header and compresses the data as it transmits it.
  It is up to the client program to look for "content-encoding" and decompress the data.
  Browsers and OPeNDAP clients do this by default. They request compressed data and
  decompress the returned data automatically.
  Other clients (e.g., Java programs) have to do this explicitly.