Easier access to scientific data
Brought to you by NOAA NMFS SWFSC ERD
|
ERDDAP at the APDRC
Easier access to scientific data |
log in
Brought to you by NOAA NMFS SWFSC ERD |
- from
Unidata,
which is used in
COARDS,
CF, and
NetCDF
data files. For example,
- the Unified Code for Units of Measure.
OGC
services such as
SOS,
WCS, and
WMS
Notes:
:
all characters other than A-Za-z0-9_-!.~'()* must be encoded as %HH,
.
| Issue | UDUNITS |
UCUM |
UDUNITS → UCUM Converter | UCUM → UDUNITS Converter |
|---|---|---|---|---|
| Character Set | UDUNITS-1 uses plain ASCII. UDUNITS-2 uses ASCII, ISO 8859-1 (Latin-1), and the UTF-8 encoding of ISO 10646 (Unicode). | Plain ASCII | All UDUNITS units with just ASCII and ISO 8859-1 characters are converted. The few units with other characters are not converted | Most UCUM units are converted. |
| case-sensitive | Yes. When different capitalizations are allowed, the variants are explicitly defined. | Yes. The converters work with the case-sensitive ("c/s") form of UCUM units. | (No changes needed) | (No changes needed) |
| Plurals and Aliases | Supports plurals and aliases for the same unit. | Uses just one abbreviation/acronym for each unit. | The various plurals and aliases are converted to the corresponding UCUM unit. Unrecognized UDUNITS names are left unchanged. | This methods tries to return common, short, single (not plural) UDUNITS aliases. Unrecognized UCUM names are left unchanged. |
| metric prefixes (e.g., "kilo" and 'k' mean "times 1000"; "µ" and 'u' means "times 10^-6") |
Supported (see UDUNITS-2 udunits2-prefixes.xml) | Supported (see the c/s column of the
prefix symbol table) |
The prefix is converted to its acronym (e.g., 'u') | The prefix is left as its acronym (e.g., 'u') |
| multiplication operators | space (most common), '-' (a typo in the spec???), '.', '*', '·' (in UDUNITS-2) | '.' | space, '*', and '·', are converted to '.' | '.' is converted to a space |
| division operators | '/', "per", "PER" | '/' | "per" and "PER" are converted to '/' | (No changes needed) |
| exponent operators | "**", '^', nothing (e.g., m-2 = m^-2) | '*' (really!), '^', nothing (e.g., m-2 = m^-2) | "**" is converted to '^'. | '*' is converted to '^'. |
| operator precedence | Exponents are highest. Then multiplication and division are evaluated left to right. | Exponents are highest. Then multiplication and division are evaluated left to right. | (No changes needed) | (No changes needed) |
| numbers | integer and floating point (e.g., 1.23456e-5) | integer only | floating point numbers are converted to rational numbers (e.g., 12.34 becomes 1234.10^-2 (remember that '.' means "times") | (No changes needed) |
| _ (underscore) | Used within individual unit names. | Used to indicate a subscript annotation within a unit name (e.g., "mo_g" for a Gregorian month) | (No changes needed) | (No changes needed) |
| ' (apostrophe) | Not used. | Used to separate words in a multi-word name (e.g., "[todd'U]" for a Todd unit) | (No changes needed) | (No changes needed) |
| ( ) | Used to group items. | Used to group items. | (No changes needed) | (No changes needed) |
| [ ] | Not used. | Used to enclose groups of symbols that should be treated as a group (e.g., "[in_i]" for an international inch) | (No changes needed) | (No changes needed) |
| { } | Not used. | Used for annotations (e.g., "%{vol}" for percent by volume). | (No changed needed) | If the comment is defined in the UCUM standard, it will be converted. If it isn't defined, it will be left intact. |
| Units | UDUNITS |
UCUM |
UDUNITS → UCUM Converter | UCUM → UDUNITS Converter |
|---|---|---|---|---|
| count | "count" is a base unit. | No exact equivalent, since it is a dimensionless non-unit. | "count" is converted to "{count}" (a dimensionless annotation). | "{count}" is converted to "count". |
| different types of degrees | UDUNITS treats degF, degC, degK, degree_north, degree_east, degree_west,
degree_true, and their aliases as separate units.
Some standards (e.g.,
COARDS and
CF), use
degree_east and degree_north to identify the longitude and latitude variables
in a data file. |
UCUM recognizes separate temperature degree units (e.g, [degF], Cel, K), but not separate direction degree units. They are all represented by "deg". | To distinguish between the various direction degree units, the converter adds a comment to direction degree units (e.g., "degree_north" becomes "deg{north}"). | If you append a comment( {east}, {north}, {west}, or {true}), the converter will convert to a direction unit (e.g., "deg{north}" becomes "degree_north"); otherwise, there is no way for the converter to generate direction degree units, so "deg" is converted to "degree". |
| specific times | UDUNITS has a system to specify specific times as
"units since ISO8601Time", e.g., "seconds since 1970-01-01T00:00:00Z". | UCUM doesn't seem to have a system to specify specific times. | The converter converts, e.g.,
"seconds since 1970-01-01T00:00:00Z" to "s{since 1970-01-01T00:00:00Z}". | The converter converts e.g.,
"s{since 1970-01-01T00:00:00Z}" to "seconds since 1970-01-01T00:00:00Z". |
| g | In UDUNITS-1, g means free-fall (although it is often mistakenly used to mean "gram").
In UDUNITS-2, g means gram. |
g means gram. [g] means free-fall. | Nothing is done. g in UDUNITS is assumed to mean gram. | g is converted to "gram". |
| F | F means Fahrenheit. | F means farad. | F is converted to [degF]. | F is converted to "farad". |
| NTU (Nephelometric Turbidity Unit) | NTU is not defined. | NTU is not defined. | NTU is converted to {ntu} following the UCUM method for noting the name of dimensionless (arbitrary) units. | {ntu} is converted to NTU. |
| PSU (Practical Salinity Units) | PSU is not defined. | PSU is not defined. | PSU and psu are converted to {psu} following the UCUM method for noting the name of dimensionless (arbitrary) units. | {psu} is converted to PSU. |