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Download Aviso SSH Dataset to ArcGIS Rasters

Downloads a time-series sea surface height dataset published by Aviso (http://www.aviso.oceanobs.com) using the OPeNDAP protocol and saves it as a sequence of ArcGIS rasters.


Command line syntax

AvisoDownloadSSHDatasetToArcGISRasters_GeoEco <username> <password> <Black Sea DT-MSLA Ref Merged | Black Sea DT-MSLA Ref Merged - Formal mapping error | Black Sea DT-MSLA Upd Merged | Black Sea DT-MSLA Upd Merged - Formal mapping error | Black Sea NRT-MSLA (Over 30 Days) Merged | Black Sea NRT-MSLA (Over 30 Days) Merged - Formal mapping error | Global DT-MADT Ref Merged | Global DT-MADT Upd Merged | Global DT-MSLA Ref Merged | Global DT-MSLA Ref Merged - Formal mapping error | Global DT-MSLA Ref Topex/Poseidon, Jason-1 | Global DT-MSLA Ref Topex/Poseidon, Jason-1 - Formal mapping error | Global DT-MSLA Upd Merged | Global DT-MSLA Upd Merged - Formal mapping error | Global NRT-MADT (Over 30 Days) Merged | Global NRT-MSLA (Over 30 Days) Merged | Global NRT-MSLA (Over 30 Days) Merged - Formal mapping error | Mediterranean DT-MADT Ref Merged | Mediterranean DT-MADT Upd Merged | Mediterranean DT-MSLA Ref Merged | Mediterranean DT-MSLA Ref Merged - Formal mapping error | Mediterranean DT-MSLA Upd Merged | Mediterranean DT-MSLA Upd Merged - Formal mapping error | Mediterranean NRT-MADT (Over 30 Days) Merged | Mediterranean NRT-MSLA (Over 30 Days) Merged | Mediterranean NRT-MSLA (Over 30 Days) Merged - Formal mapping error> <startDate> <endDate> <outputWorkspace> {rasterNameExpression} {zeroTo360} {projectedCoordinateSystem} {geographicTransformation} {NEAREST | BILINEAR | CUBIC} {projectedCellSize} {registrationPoint} {clippingRectangle} {mapAlgebraExpression} {buildPyramids} {skipExisting}

Parameters
ExpressionExplanation
<username>

Your Aviso username.

To access Aviso datasets with OPeNDAP, you must first obtain a username and password from Aviso. Please see http://www.aviso.oceanobs.com/en/data/ for instructions on obtaining a username and password.

Starting August 2010, Aviso allowed temporary access to the general public with the username "aviso-users" and the password "grid2010". If you do not have a username and password yet, you can try those ones. Aviso explained that those ones would only work for a limited time. If they do not work for you, please contact Aviso to obtain your own unique username and password.

<password>

Your Aviso password.

Please see the documentation for the Aviso Username parameter above for more information about the username and password parameters.

<Black Sea DT-MSLA Ref Merged | Black Sea DT-MSLA Ref Merged - Formal mapping error | Black Sea DT-MSLA Upd Merged | Black Sea DT-MSLA Upd Merged - Formal mapping error | Black Sea NRT-MSLA (Over 30 Days) Merged | Black Sea NRT-MSLA (Over 30 Days) Merged - Formal mapping error | Global DT-MADT Ref Merged | Global DT-MADT Upd Merged | Global DT-MSLA Ref Merged | Global DT-MSLA Ref Merged - Formal mapping error | Global DT-MSLA Ref Topex/Poseidon, Jason-1 | Global DT-MSLA Ref Topex/Poseidon, Jason-1 - Formal mapping error | Global DT-MSLA Upd Merged | Global DT-MSLA Upd Merged - Formal mapping error | Global NRT-MADT (Over 30 Days) Merged | Global NRT-MSLA (Over 30 Days) Merged | Global NRT-MSLA (Over 30 Days) Merged - Formal mapping error | Mediterranean DT-MADT Ref Merged | Mediterranean DT-MADT Upd Merged | Mediterranean DT-MSLA Ref Merged | Mediterranean DT-MSLA Ref Merged - Formal mapping error | Mediterranean DT-MSLA Upd Merged | Mediterranean DT-MSLA Upd Merged - Formal mapping error | Mediterranean NRT-MADT (Over 30 Days) Merged | Mediterranean NRT-MSLA (Over 30 Days) Merged | Mediterranean NRT-MSLA (Over 30 Days) Merged - Formal mapping error>

Aviso sea surface height product download. Please http://www.aviso.oceanobs.com/en/data/ for descriptions of the products.

At the time of this writing, this tool supported all of the SSH products that Aviso made available for download over OPeNDAP. If you find that Aviso publishes a new product that is not available using this tool, please contact the author of this tool to have support for it added. As a workaround, you can also use the generic Download Aviso Dataset to ArcGIS Rasters tool, which accepts an OPeNDAP URL.

Aviso does not make all of its products available over OPeNDAP. If the product you need is not available, you can download the netCDF files and use MGET's conversion utilities to create ArcGIS rasters from them.

The product name that you must pass for this parameter is case sensitive. If you invoke this tool programmatically, be sure to specify the product name using the proper case.

<startDate>

Start date for the images to download. Images that occur on or after the start date and on or before the end date will be downloaded.

<endDate>

End date for the images to download. Images that occur on or after the start date and on or before the end date will be downloaded.

<outputWorkspace>

Workspace to receive the rasters.

{rasterNameExpression}

Expression that specifies how to generate an output raster name from an image date.

The expression is a string that contains codes that are replaced with components of the image date. For example:

ssh%Y%j

This expression means "ssh followed by the four-digit year and three digit day-of-the-year". For example, if you downloaded images for 1-Jan-2008, 2-Jan-2008, and 3-Jan-2008, this expression would name the output rasters:

ssh2008001
ssh2008002
ssh2008003

If you are downloading a lot of images and storing them in a directory, you might want to create subdirectories by year. For example:

%Y/ssh%Y%j

From the dates above, you'd get:

2008/ssh2008001
2008/ssh2008002
2008/ssh2008003

(This example uses the forward slash character to indicate a subdirectory. On Microsoft operating systems, both a forward slash and a back slash can be used to indicate a subdirectory. The advantage of a forward slash is that it works on other operating systems as well.)

The possible date component codes are:

%d - Day of the month as a decimal number [01,31].

%H - Hour (24-hour clock) as a decimal number [00,23].

%I - Hour (12-hour clock) as a decimal number [01,12].

%j - Day of the year as a decimal number [001,366].

%m - Month as a decimal number [01,12].

%M - Minute as a decimal number [00,59].

%p - Locale's equivalent of either AM or PM (use with %I).

%S - Second as a decimal number [00,61].

%U - Week number of the year (Sunday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Sunday are considered to be in week 0. (3)

%w - Weekday as a decimal number [0(Sunday),6].

%W - Week number of the year (Monday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Monday are considered to be in week 0. (3)

%y - Year without century as a decimal number [00,99].

%Y - Year with century as a decimal number.

%% - A literal "%" character.

{zeroTo360}

This parameter only applies to global datasets. It will be ignored for regional datasets (e.g. the Mediterranean).

If True, the output rasters will be centered on the International Date Line; rasters in a geographic projection will use a 0-to-360 coordinate system. This is appropriate for studies that encompass the central Pacific ocean.

If False, the output rasters will be centered on the Prime Meridian; rasters in a geographic projection will use a -180 to +180 coordinate system. This is the traditional orientation for ArcGIS data.

{projectedCoordinateSystem}

New coordinate system to project the output raster to.

The raster will originally be in one of the following coordinate systems:

  • Sphere_Mercator - Mercator projection on a sphere. At the time of this writing, all of the Aviso data available over OPeNDAP that used a Mercator projection used this one. Aviso's documentation did not specify the radius of the sphere. Because the dimensions of the raster cells remain the same in the angular coordinates regardless of the sphere's radius, I selected the radius 6371000.0 because it allowed me to use "Mercator (sphere)" projection that comes predefined in ArcGIS. For more information about Aviso's Mercator projection, please see the Aviso's SSALTO/DUACS User Handbook: (M)SLA and (M)ADT Near-Real Time and Delayed Time Products, section 2.1.7.2: Maps projection. At the time of this writing, that documentation was very terse, consisting mainly of equations, but if you follow it closely you will find no metion of an ellipsoid and see that they are performing calculations on a sphere.

  • GCS_WGS_1984 - geographic coordinates, WGS 1984 datum. This coordinate system will be used for data that are in what Aviso calls "cartesian grids" or "regular grids", often at a 0.25 or 0.125 degree cell size.

It is unfortunate for ArcGIS users that Aviso uses a spherical Mercator projection rather than a Mercator projection based on a common ellipsoid such as WGS 1984. Many users will want to project the data to a coordinate system that uses their datum of choice, to avoid ArcGIS warnings about different datums. For your convenience, this tool allows you to do so as a post-processing operation.

The ArcGIS Project Raster tool is used to perform the projection. The documentation for that tool recommends that you also specify a cell size for the new coordinate system.

I have noticed that for certain coordinate systems the ArcGIS 9.2 Project Raster tool seems to clip the projected raster to an arbitrary extent that is too small. For example, when projecting a global MODIS Aqua 4 km chlorophyll image in geographic coordinates to Lambert_Azimuthal_Equal_Area with central meridian of -60 and latitude of origin of -63, the resulting image is clipped to show only one-quarter of the planet. This problem does not occur when Project Raster is invoked interactively from the ArcGIS user interface; it only occurs when the tool is invoked programmatically (the ProjectRaster_management method of the geoprocessor). Thus you may not see it when you use Project Raster yourself but it may happen when you use MGET tools that invoke Project Raster as part of their geoprocessing operations.

If you encounter this problem, you can work around it like this:

  • First, run this tool without specifying a new coordinate system, to obtain the output raster in the original coordinate system.

  • In ArcCatalog, use the Project Raster tool to project the raster to the new coordinate system. Verify that the entire raster is present, that it has not been clipped to an extent that is too small.

  • In ArcCatalog, look up the extent of the projected raster by right-clicking on it in the catalog tree, selecting Properties, and scrolling down to Extent.

  • Now, before running this tool, set the Extent environment setting to the values you looked up. If you are invoking the tool interactively from ArcCatalog or ArcMap, click the Environments button on the tool's dialog box, open General Settings, change the Extent drop-down to "As Specified Below", and type in the values you looked up. If you're invoking it from a geoprocessing model, right-click on the tool in the model, select Make Variable, From Environment, General Settings, Extent. This will place Extent as a variable in your model, attached to the tool. Open the Extent variable, change it to "As Specified Below" and type in the values you looked up. If you're invoking the tool programmatically, you must set the Extent property of the geoprocessor to the values you looked up. Please see the ArcGIS documentation for more information about this and Environment settings in general.

  • Run this tool. The extent of the output raster should now be the proper size.

{geographicTransformation}

A transformation method used to convert between the original coordinate system and the new coordinate system.

This parameter is a new option introduced by ArcGIS 9.2. You must have ArcGIS 9.2 to use this parameter.

This parameter is only needed when you specify that the raster should be projected to a new coordinate system and that new system uses a different datum than the original coordinate system, or there is some other difference between the two coordinate systems that requires a transformation. To determine if a transformation is needed, I recommend the following procedure:

  • First, run this tool without specifying a new coordinate system, to obtain the raster in the original coordinate system.

  • Next, use the ArcGIS 9.2 Project Raster tool on the raster to project it to the desired coordinate system. If a geographic transformation is needed, that tool will prompt you for one. Write down the exact name of the transformation you used.

  • Finally, if a transformation was needed, type in the exact name into this tool, rerun it, and verify that the raster was projected as you desired.

{NEAREST | BILINEAR | CUBIC}

The resampling algorithm to be used to project the original raster to a new coordinate system. The ArcGIS Project Raster tool is used to perform the projection and accepts the following values:

  • NEAREST - nearest neighbor interpolation

  • BILINEAR - bilinear interpolation

  • CUBIC - cubic convolution

You must specify one of these algorithms to project to a new coordinate system. An error will be raised if you specify a new coordinate system without selecting an algorithm.

{projectedCellSize}

The cell size of the projected coordinate system. Although this parameter is optional, to receive the best results, the ArcGIS documentation recommends you always specify it when projecting to a new coordinate system.

{registrationPoint}

The x and y coordinates (in the output space) used for pixel alignment.

This parameter is a new option introduced by ArcGIS 9.2. You must have ArcGIS 9.2 to use this parameter. It is ignored if you do not specify that the raster should be projected to a new coordinate system.

{clippingRectangle}

Rectangle to which the raster should be clipped.

If a projected coordinate system was specified, the clipping is performed after the projection and the rectangle's coordinates should be specified in the new coordinate system. If no projected coordinate system was specified, the coordinates should be specified in the original coordinate system.

The ArcGIS Clip tool is used to perfom the clip. The clipping rectangle must be passed to this tool as a string of four numbers separated by spaces. The ArcGIS user interface automatically formats the string properly; when invoking this tool from the ArcGIS UI, you need not worry about the format. But when invoking it programmatically, take care to provide a properly-formatted string. The numbers are ordered LEFT, BOTTOM, RIGHT, TOP. For example, if the raster is in a geographic coordinate system, it may be clipped to 10 W, 15 S, 20 E, and 25 N with the string:

10 15 20 25

Integers or decimal numbers may be provided.

{mapAlgebraExpression}

Map algebra expression to execute on the raster.

WARNING: The ArcGIS Geoprocessing Model Builder may randomly and silently delete the value of this parameter. This is a bug in ArcGIS. Before running a model that you have saved, open this tool and validate that the parameter value still exists.

The expression is executed after the converted raster is projected and clipped (if those options are specified). Use the case-sensitive string inputRaster to represent the raster that you now want to perform map algebra upon. For example, to convert the raster to an integer raster and add 1 to all of the cells, use this expression:

int(inputRaster) + 1

The string inputRaster is case-sensitive. Prior to executing the map algebra expression, the string is replaced with the path to a temporary raster that represents the raster being generated. The final expression must be less than 4000 characters long or ArcGIS will report an error.

The ArcGIS Single Output Map Algebra tool is used to execute the map algebra expression. You must have a license for the ArcGIS Spatial Analyst extension in order to perform map algebra.

Map algebra syntax can be very picky. Here are some tips that will help you succeed with this tool:

  • Before using this tool, construct and test out your map algebra expression using the ArcGIS Single Output Map Algebra tool. Then paste the expression into this tool and edit it to use the inputRaster variable rather than the test value you used with Single Output Map Algebra.

  • If you do develop your expression directly in this tool, start with a very simple expression. Verify that it works properly, add a little to it, and verify again. Repeat this process until you have built up the complete expression.

  • Always separate mathematical operators from raster paths using spaces. In the example above, the / operator contains a space on either side. Follow this pattern. In some circumstances, ArcGIS will fail to process raster algebra expressions that do not separate raster paths from operators using spaces. The reported error message usually does not indicate that this is the problem, and tracking it down can be very frustrating.

{buildPyramids}

If True, pyramids will be built for the raster, which will improve its display speed in the ArcGIS user interface.

{skipExisting}

If True, the download will be skipped for output rasters that already exist.

Scripting syntax

AvisoDownloadSSHDatasetToArcGISRasters_GeoEco (username, password, product, startDate, endDate, outputWorkspace, rasterNameExpression, zeroTo360, projectedCoordinateSystem, geographicTransformation, resamplingTechnique, projectedCellSize, registrationPoint, clippingRectangle, mapAlgebraExpression, buildPyramids, skipExisting)

Parameters
ExpressionExplanation
Aviso username (Required)

Your Aviso username.

To access Aviso datasets with OPeNDAP, you must first obtain a username and password from Aviso. Please see http://www.aviso.oceanobs.com/en/data/ for instructions on obtaining a username and password.

Starting August 2010, Aviso allowed temporary access to the general public with the username "aviso-users" and the password "grid2010". If you do not have a username and password yet, you can try those ones. Aviso explained that those ones would only work for a limited time. If they do not work for you, please contact Aviso to obtain your own unique username and password.

Aviso password (Required)

Your Aviso password.

Please see the documentation for the Aviso Username parameter above for more information about the username and password parameters.

Aviso SSH product to download (Required)

Aviso sea surface height product download. Please http://www.aviso.oceanobs.com/en/data/ for descriptions of the products.

At the time of this writing, this tool supported all of the SSH products that Aviso made available for download over OPeNDAP. If you find that Aviso publishes a new product that is not available using this tool, please contact the author of this tool to have support for it added. As a workaround, you can also use the generic Download Aviso Dataset to ArcGIS Rasters tool, which accepts an OPeNDAP URL.

Aviso does not make all of its products available over OPeNDAP. If the product you need is not available, you can download the netCDF files and use MGET's conversion utilities to create ArcGIS rasters from them.

The product name that you must pass for this parameter is case sensitive. If you invoke this tool programmatically, be sure to specify the product name using the proper case.

Start date (Required)

Start date for the images to download. Images that occur on or after the start date and on or before the end date will be downloaded.

End date (Required)

End date for the images to download. Images that occur on or after the start date and on or before the end date will be downloaded.

Output workspace (Required)

Workspace to receive the rasters.

Output raster name expression (Optional)

Expression that specifies how to generate an output raster name from an image date.

The expression is a string that contains codes that are replaced with components of the image date. For example:

ssh%Y%j

This expression means "ssh followed by the four-digit year and three digit day-of-the-year". For example, if you downloaded images for 1-Jan-2008, 2-Jan-2008, and 3-Jan-2008, this expression would name the output rasters:

ssh2008001
ssh2008002
ssh2008003

If you are downloading a lot of images and storing them in a directory, you might want to create subdirectories by year. For example:

%Y/ssh%Y%j

From the dates above, you'd get:

2008/ssh2008001
2008/ssh2008002
2008/ssh2008003

(This example uses the forward slash character to indicate a subdirectory. On Microsoft operating systems, both a forward slash and a back slash can be used to indicate a subdirectory. The advantage of a forward slash is that it works on other operating systems as well.)

The possible date component codes are:

%d - Day of the month as a decimal number [01,31].

%H - Hour (24-hour clock) as a decimal number [00,23].

%I - Hour (12-hour clock) as a decimal number [01,12].

%j - Day of the year as a decimal number [001,366].

%m - Month as a decimal number [01,12].

%M - Minute as a decimal number [00,59].

%p - Locale's equivalent of either AM or PM (use with %I).

%S - Second as a decimal number [00,61].

%U - Week number of the year (Sunday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Sunday are considered to be in week 0. (3)

%w - Weekday as a decimal number [0(Sunday),6].

%W - Week number of the year (Monday as the first day of the week) as a decimal number [00,53]. All days in a new year preceding the first Monday are considered to be in week 0. (3)

%y - Year without century as a decimal number [00,99].

%Y - Year with century as a decimal number.

%% - A literal "%" character.

Use 0-to-360 orientation (Optional)

This parameter only applies to global datasets. It will be ignored for regional datasets (e.g. the Mediterranean).

If True, the output rasters will be centered on the International Date Line; rasters in a geographic projection will use a 0-to-360 coordinate system. This is appropriate for studies that encompass the central Pacific ocean.

If False, the output rasters will be centered on the Prime Meridian; rasters in a geographic projection will use a -180 to +180 coordinate system. This is the traditional orientation for ArcGIS data.

Project to new coordinate system (Optional)

New coordinate system to project the output raster to.

The raster will originally be in one of the following coordinate systems:

  • Sphere_Mercator - Mercator projection on a sphere. At the time of this writing, all of the Aviso data available over OPeNDAP that used a Mercator projection used this one. Aviso's documentation did not specify the radius of the sphere. Because the dimensions of the raster cells remain the same in the angular coordinates regardless of the sphere's radius, I selected the radius 6371000.0 because it allowed me to use "Mercator (sphere)" projection that comes predefined in ArcGIS. For more information about Aviso's Mercator projection, please see the Aviso's SSALTO/DUACS User Handbook: (M)SLA and (M)ADT Near-Real Time and Delayed Time Products, section 2.1.7.2: Maps projection. At the time of this writing, that documentation was very terse, consisting mainly of equations, but if you follow it closely you will find no metion of an ellipsoid and see that they are performing calculations on a sphere.

  • GCS_WGS_1984 - geographic coordinates, WGS 1984 datum. This coordinate system will be used for data that are in what Aviso calls "cartesian grids" or "regular grids", often at a 0.25 or 0.125 degree cell size.

It is unfortunate for ArcGIS users that Aviso uses a spherical Mercator projection rather than a Mercator projection based on a common ellipsoid such as WGS 1984. Many users will want to project the data to a coordinate system that uses their datum of choice, to avoid ArcGIS warnings about different datums. For your convenience, this tool allows you to do so as a post-processing operation.

The ArcGIS Project Raster tool is used to perform the projection. The documentation for that tool recommends that you also specify a cell size for the new coordinate system.

I have noticed that for certain coordinate systems the ArcGIS 9.2 Project Raster tool seems to clip the projected raster to an arbitrary extent that is too small. For example, when projecting a global MODIS Aqua 4 km chlorophyll image in geographic coordinates to Lambert_Azimuthal_Equal_Area with central meridian of -60 and latitude of origin of -63, the resulting image is clipped to show only one-quarter of the planet. This problem does not occur when Project Raster is invoked interactively from the ArcGIS user interface; it only occurs when the tool is invoked programmatically (the ProjectRaster_management method of the geoprocessor). Thus you may not see it when you use Project Raster yourself but it may happen when you use MGET tools that invoke Project Raster as part of their geoprocessing operations.

If you encounter this problem, you can work around it like this:

  • First, run this tool without specifying a new coordinate system, to obtain the output raster in the original coordinate system.

  • In ArcCatalog, use the Project Raster tool to project the raster to the new coordinate system. Verify that the entire raster is present, that it has not been clipped to an extent that is too small.

  • In ArcCatalog, look up the extent of the projected raster by right-clicking on it in the catalog tree, selecting Properties, and scrolling down to Extent.

  • Now, before running this tool, set the Extent environment setting to the values you looked up. If you are invoking the tool interactively from ArcCatalog or ArcMap, click the Environments button on the tool's dialog box, open General Settings, change the Extent drop-down to "As Specified Below", and type in the values you looked up. If you're invoking it from a geoprocessing model, right-click on the tool in the model, select Make Variable, From Environment, General Settings, Extent. This will place Extent as a variable in your model, attached to the tool. Open the Extent variable, change it to "As Specified Below" and type in the values you looked up. If you're invoking the tool programmatically, you must set the Extent property of the geoprocessor to the values you looked up. Please see the ArcGIS documentation for more information about this and Environment settings in general.

  • Run this tool. The extent of the output raster should now be the proper size.

Geographic transformation (Optional)

A transformation method used to convert between the original coordinate system and the new coordinate system.

This parameter is a new option introduced by ArcGIS 9.2. You must have ArcGIS 9.2 to use this parameter.

This parameter is only needed when you specify that the raster should be projected to a new coordinate system and that new system uses a different datum than the original coordinate system, or there is some other difference between the two coordinate systems that requires a transformation. To determine if a transformation is needed, I recommend the following procedure:

  • First, run this tool without specifying a new coordinate system, to obtain the raster in the original coordinate system.

  • Next, use the ArcGIS 9.2 Project Raster tool on the raster to project it to the desired coordinate system. If a geographic transformation is needed, that tool will prompt you for one. Write down the exact name of the transformation you used.

  • Finally, if a transformation was needed, type in the exact name into this tool, rerun it, and verify that the raster was projected as you desired.

Projection resampling technique (Optional)

The resampling algorithm to be used to project the original raster to a new coordinate system. The ArcGIS Project Raster tool is used to perform the projection and accepts the following values:

  • NEAREST - nearest neighbor interpolation

  • BILINEAR - bilinear interpolation

  • CUBIC - cubic convolution

You must specify one of these algorithms to project to a new coordinate system. An error will be raised if you specify a new coordinate system without selecting an algorithm.

Cell size for projected coordinate system (Optional)

The cell size of the projected coordinate system. Although this parameter is optional, to receive the best results, the ArcGIS documentation recommends you always specify it when projecting to a new coordinate system.

Registration point for projected coordinate system (Optional)

The x and y coordinates (in the output space) used for pixel alignment.

This parameter is a new option introduced by ArcGIS 9.2. You must have ArcGIS 9.2 to use this parameter. It is ignored if you do not specify that the raster should be projected to a new coordinate system.

Clip to rectangle (Optional)

Rectangle to which the raster should be clipped.

If a projected coordinate system was specified, the clipping is performed after the projection and the rectangle's coordinates should be specified in the new coordinate system. If no projected coordinate system was specified, the coordinates should be specified in the original coordinate system.

The ArcGIS Clip tool is used to perfom the clip. The clipping rectangle must be passed to this tool as a string of four numbers separated by spaces. The ArcGIS user interface automatically formats the string properly; when invoking this tool from the ArcGIS UI, you need not worry about the format. But when invoking it programmatically, take care to provide a properly-formatted string. The numbers are ordered LEFT, BOTTOM, RIGHT, TOP. For example, if the raster is in a geographic coordinate system, it may be clipped to 10 W, 15 S, 20 E, and 25 N with the string:

10 15 20 25

Integers or decimal numbers may be provided.

Execute map algebra expression (Optional)

Map algebra expression to execute on the raster.

WARNING: The ArcGIS Geoprocessing Model Builder may randomly and silently delete the value of this parameter. This is a bug in ArcGIS. Before running a model that you have saved, open this tool and validate that the parameter value still exists.

The expression is executed after the converted raster is projected and clipped (if those options are specified). Use the case-sensitive string inputRaster to represent the raster that you now want to perform map algebra upon. For example, to convert the raster to an integer raster and add 1 to all of the cells, use this expression:

int(inputRaster) + 1

The string inputRaster is case-sensitive. Prior to executing the map algebra expression, the string is replaced with the path to a temporary raster that represents the raster being generated. The final expression must be less than 4000 characters long or ArcGIS will report an error.

The ArcGIS Single Output Map Algebra tool is used to execute the map algebra expression. You must have a license for the ArcGIS Spatial Analyst extension in order to perform map algebra.

Map algebra syntax can be very picky. Here are some tips that will help you succeed with this tool:

  • Before using this tool, construct and test out your map algebra expression using the ArcGIS Single Output Map Algebra tool. Then paste the expression into this tool and edit it to use the inputRaster variable rather than the test value you used with Single Output Map Algebra.

  • If you do develop your expression directly in this tool, start with a very simple expression. Verify that it works properly, add a little to it, and verify again. Repeat this process until you have built up the complete expression.

  • Always separate mathematical operators from raster paths using spaces. In the example above, the / operator contains a space on either side. Follow this pattern. In some circumstances, ArcGIS will fail to process raster algebra expressions that do not separate raster paths from operators using spaces. The reported error message usually does not indicate that this is the problem, and tracking it down can be very frustrating.

Build pyramids (Optional)

If True, pyramids will be built for the raster, which will improve its display speed in the ArcGIS user interface.

Skip existing outputs (Optional)

If True, the download will be skipped for output rasters that already exist.