CRCCalculator

Calculates a CRC (Cyclic Redundancy Check) value for a feature and places the calculated CRC value into the attribute specified.

If a CRC is calculated for both coordinates and attributes, it is returned as a hexadecimal string representing an integer of double the bit-length of the chosen algorithm. If a CRC is calculated for only coordinates, only attributes, or a file, it is returned as a hexadecimal string representing an integer equal to the algorithm bit-length.

In the case where the CRC of both coordinates and attributes is being calculated, the format of the CRC attribute string is xxxxxxxxyyyyyyyy, where the x's represent the CRC calculated for the coordinates, and the y's represent the CRC calculated for the combination of the coordinates and attributes. The first half of the CRC (the x's) in this case will match the entire CRC of calculating only the geometry coordinates. The second half of the CRC (the y's) will not match the entire CRC of calculating only attributes.

MD5 checksums do not follow this pattern and are instead returned as a 32 digit hex-string which is calculated based on the entire input.

Usage Notes

You can use this CRC value to check data at a later date - to make sure it hasn't been changed, corrupted, deleted etc. It can also be used as a form of ChangeDetection (instead of using the ChangeDetector to compare geometry, use the Matcher to compare CRC values).

Like all popular CRC algorithms, different features could produce the same CRC value with minimal probability.

Example

This FME Community example shows an advantage to using the CRCCalculator over the ChangeDetector.

Configuration

Input Ports

Output Ports

Note Feature order may change in relation to other output ports. Feature order per port is maintained.

Parameters

General

CRC Algorithm	The algorithm chosen will determine the parameters used for the CRC calculation based on CRC standards. These standards can be found at: https://reveng.sourceforge.io/crc-catalogue/ The algorithms to choose from are: CRC-16-CCITT-FALSE CRC-16-XMODEM CRC-16-ARC CRC-32 CRC-32-Q MD5
Calculate CRC On	The CRC can be calculated on either Coordinates and Selected Attributes, Coordinates and All Attributes, Selected Attributes Only, All Attributes Only, or File. Coordinates refers to the coordinates of the geometries of input features. If Coordinates and Selected Attributes is specified, the CRC will be calculated on the coordinates and the values of the attributes the user has selected in the Selected Attributes parameter. If Coordinates and All Attributes is specified, the CRC will be calculated on the coordinates and the values of all the attributes on the feature. For both of the above options, if no attributes with a value are found, the calculated CRC will be based only on the feature's coordinates. If no coordinates or attributes are found, 0 is returned (except for the MD5 algorithm, which returns d41d8cd98f00b204e9800998ecf8427e). If Selected Attributes Only is specified, the CRC will be calculated on the values of the attributes the user has selected in the Selected Attributes parameter. If All Attributes Only is specified, the CRC will be calculated on the values of all the attributes on the feature. For Selected Attributes Only and All Attributes Only options, if no attributes with a value are found, the output CRC value is 0 (except for the MD5 algorithm, which returns d41d8cd98f00b204e9800998ecf8427e). If File is specified, the CRC will be calculated on the contents of the file specified in the Filename parameter. If the file cannot be found, the feature will be rejected.
Selected Attributes	If Calculate CRC On is set to Coordinates and Selected Attributes or Selected Attributes Only, this parameter indicates the attributes to use in the CRC calculation.
Filename	When Calculate CRC On is set to File, this parameter is used to specify the file to calculate the CRC value for.

Editing Transformer Parameters

Using a set of menu options, transformer parameters can be assigned by referencing other elements in the workspace. More advanced functions, such as an advanced editor and an arithmetic editor, are also available in some transformers. To access a menu of these options, click beside the applicable parameter. For more information, see Transformer Parameter Menu Options.

Defining Values

There are several ways to define a value for use in a Transformer. The simplest is to simply type in a value or string, which can include functions of various types such as attribute references, math and string functions, and workspace parameters. There are a number of tools and shortcuts that can assist in constructing values, generally available from the drop-down context menu adjacent to the value field.

How to Set Parameter Values

Using the Text Editor

The Text Editor provides a convenient way to construct text strings (including regular expressions) from various data sources, such as attributes, parameters, and constants, where the result is used directly inside a parameter.

Text Editor

Using the Arithmetic Editor

The Arithmetic Editor provides a convenient way to construct math expressions from various data sources, such as attributes, parameters, and feature functions, where the result is used directly inside a parameter.

Arithmetic Editor

Conditional Values

Set values depending on one or more test conditions that either pass or fail.

Parameter Condition Definition Dialog

Content

Expressions and strings can include a number of functions, characters, parameters, and more.

When setting values - whether entered directly in a parameter or constructed using one of the editors - strings and expressions containing String, Math, Date/Time or FME Feature Functions will have those functions evaluated. Therefore, the names of these functions (in the form @<function_name>) should not be used as literal string values.

Content Types

String Functions	These functions manipulate and format strings.
Special Characters	A set of control characters is available in the Text Editor.
Math Functions	Math functions are available in both editors.
Date/Time Functions	Date and time functions are available in the Text Editor.
Math Operators	These operators are available in the Arithmetic Editor.
FME Feature Functions	These return primarily feature-specific values.
FME Parameters	FME and workspace-specific parameters may be used.
Creating and Modifying User Parameters	Create your own editable parameters.

Dialog Options - Tables

Transformers with table-style parameters have additional tools for populating and manipulating values.

Table Tools

Row Reordering

Enabled once you have clicked on a row item. Choices include:

Add a row
Remove a row
Move current row up one
Move current row down one
Move current row to top
Move current row to bottom

Cut, Copy, and Paste

Enabled once you have clicked on a row item. Choices include:

Cut a row - delete and copy to clipboard
Copy a row to the clipboard
Paste a row from the clipboard

Cut, copy, and paste may be used within a transformer, or between transformers.

Filter

Start typing a string, and the matrix will only display rows matching those characters. Searches all columns. This only affects the display of attributes within the transformer - it does not alter which attributes are output.

Import

Import populates the table with a set of new attributes read from a dataset. Specific application varies between transformers.

Reset/Refresh

Generally resets the table to its initial state, and may provide additional options to remove invalid entries. Behavior varies between transformers.

Note: Not all tools are available in all transformers.

FME Community

The FME Community is the place for demos, how-tos, articles, FAQs, and more. Get answers to your questions, learn from other users, and suggest, vote, and comment on new features.

Search for all results about the CRCCalculator on the FME Community.