# gie¶

The Geospatial Integrity Investigation Environment

## Synopsis¶

gie [ -hovql [ args ] ] file[s]

## Description¶

gie, the Geospatial Integrity Investigation Environment, is a regression testing environment for the PROJ transformation library. Its primary design goal is to be able to perform regression testing of code that are a part of PROJ, while not requiring any other kind of tooling than the same C compiler already employed for compiling the library.

-h, --help

Print usage information

-o <file>, --output <file>

Specify output file name

-v, --verbose

Verbose: Provide non-essential informational output. Repeat -v for more verbosity (e.g. -vv)

-q, --quiet

Quiet: Opposite of verbose. In quiet mode not even errors are reported. Only interaction is through the return code (0 on success, non-zero indicates number of FAILED tests)

-l, --list

List the PROJ internal system error codes

--version

Print version number

Tests for gie are defined in simple text files. Usually having the extension .gie. Test for gie are written in the purpose-build command language for gie. The basic functionality of the gie command language is implemented through just 3 command verbs: operation, which defines the PROJ operation to test, accept, which defines the input coordinate to read, and expect, which defines the result to expect.

A sample test file for gie that uses the three above basic commands looks like:

<gie>

--------------------------------------------
Test output of the UTM projection
--------------------------------------------
operation  +proj=utm  +zone=32  +ellps=GRS80
--------------------------------------------
accept     12  55
expect     691_875.632_14   6_098_907.825_05

</gie>


Parsing of a gie file starts at <gie> and ends when </gie> is reached. Anything before <gie> and after </gie> is not considered. Test cases are created by defining an operation which accept an input coordinate and expect an output coordinate.

Because gie tests are wrapped in the <gie>/</gie> tags it is also possible to add test cases to custom made init files. The tests will be ignore by PROJ when reading the init file with +init and gie ignores anything not wrapped in <gie>/</gie>.

gie tests are defined by a set of commands like operation, accept and expect in the example above. Together the commands make out the gie command language. Any line in a gie file that does not start with a command is ignored. In the example above it is seen how this can be used to add comments and styling to gie test files in order to make them more readable as well as documenting what the purpose of the various tests are.

Below the gie command language is explained in details.

## Examples¶

1. Run all tests in a file with all debug information turned on
gie -vvvv corner-cases.gie

1. Run all tests in several files
gie foo bar


## gie command language¶

operation <+args>

Define a PROJ operation to test. Example:

operation proj=utm zone=32 ellps=GRS80
# test 4D function
accept    12 55 0 0
expect    691875.63214  6098907.82501  0  0

# test 2D function
accept    12 56
expect    687071.4391   6210141.3267

accept <x y [z [t]]>

Define the input coordinate to read. Takes test coordinate. The coordinate can be defined by either 2, 3 or 4 values, where the first two values are the x- and y-components, the 3rd is the z-component and the 4th is the time component. The number of components in the coordinate determines which version of the operation is tested (2D, 3D or 4D). Many coordinates can be accepted for one operation. For each accept an accompanying expect is needed.

Note that gie accepts the underscore (_) as a thousands separator. It is not required (in fact, it is entirely ignored by the input routine), but it significantly improves the readability of the very long strings of numbers typically required in projected coordinates.

See operation for an example.

expect <x y [z [t]]> | <error code>

Define the expected coordinate that will be returned from accepted coordinate passed though an operation. The expected coordinate can be defined by either 2, 3 or 4 components, similarly to accept. Many coordinates can be expected for one operation. For each expect an accompanying accept is needed.

See operation for an example.

In addition to expecting a coordinate it is also possible to expect a PROJ error code in case an operation can’t be created. This is useful when testing that errors are caught and handled correctly. Below is an example of that tests that the pipeline operator fails correctly when a non-invertible pipeline is constructed.

operation   proj=pipeline step
proj=urm5 n=0.5 inv
expect      failure pjd_err_malformed_pipeline


See gie --list for a list of error codes that can be expected.

tolerance <tolerance>

The tolerance command controls how much accepted coordinates can deviate from the expected coordinate. This is handy to test that an operation meets a certain numerical tolerance threshold. Some operations are expected to be accurate within millimeters where others might only be accurate within a few meters. tolerance should

operation       proj=merc
# test coordinate as returned by echo 12 55 | proj +proj=merc
tolerance       1 cm
accept          12 55
expect          1335833.89 7326837.72

# test that the same coordinate with a 50 m false easting as determined
# by echo 12 55 |proj +proj=merc +x_0=50 is still within a 100 m
# tolerance of the unaltered coordinate from proj=merc
tolerance       100 m
accept          12 55
expect          1335883.89  7326837.72


The default tolerance is 0.5 mm. See proj -lu for a list of possible units.

roundtrip <n> <tolerance>

Do a roundtrip test of an operation. roundtrip needs a operation and a accept command to function. The accepted coordinate is passed to the operation first in it’s forward mode, then the output from the forward operation is passed back to the inverse operation. This procedure is done n times. If the resulting coordinate is within the set tolerance of the initial coordinate, the test is passed.

Example with the default 100 iterations and the default tolerance:

operation       proj=merc
accept          12 55
roundtrip


Example with count and default tolerance:

operation       proj=merc
accept          12 55
roundtrip       10000


Example with count and tolerance:

operation       proj=merc
accept          12 55
roundtrip       10000 5 mm

direction <direction>

The direction command specifies in which direction an operation is performed. This can either be forward or inverse. An example of this is seen below where it is tested that a symmetrical transformation pipeline returns the same results in both directions.

operation proj=pipeline zone=32 step
proj=utm  ellps=GRS80 step
proj=utm  ellps=GRS80 inv
tolerance 0.1 mm

accept 12 55 0 0
expect 12 55 0 0

# Now the inverse direction (still same result: the pipeline is symmetrical)

direction inverse
expect 12 55 0 0


The default direction is “forward”.

ignore <error code>

This is especially useful in test cases that rely on a grid that is not guaranteed to be available. Below is an example of that situation.

operation proj=hgridshift +grids=nzgd2kgrid0005.gsb ellps=GRS80
tolerance 1 mm
accept    172.999892181021551 -45.001620431954613
expect    173                 -45


See gie --list for a list of error codes that can be ignored.

require_grid <grid_name>

Checks the availability of the grid <grid_name>. If it is not found, then all accept/expect pairs until the next operation will be skipped. require_grid can be repeated several times to specify several grids whose presence is required.

echo <text>

Add user defined text to the output stream. See the example below.

<gie>
echo ** Mercator projection tests **
operation +proj=merc
accept  0   0
expect  0   0
</gie>


which returns

-------------------------------------------------------------------------------
** Mercator projection test **
-------------------------------------------------------------------------------
total:  1 tests succeeded,  0 tests skipped,  0 tests failed.
-------------------------------------------------------------------------------

skip

Skip any test after the first occurrence of skip. In the example below only the first test will be performed. The second test is skipped. This feature is mostly relevant for debugging when writing new test cases.

<gie>
operation proj=merc
accept  0   0
expect  0   0
skip
accept  0   1
expect  0   110579.9
</gie>


## Background¶

More importantly than being an acronym for “Geospatial Integrity Investigation Environment”, gie were also the initials, user id, and USGS email address of Gerald Ian Evenden (1935–2016), the geospatial visionary, who, already in the 1980s, started what was to become the PROJ of today.

Gerald’s clear vision was that map projections are just special functions. Some of them rather complex, most of them of two variables, but all of them just special functions, and not particularly more special than the sin(), cos(), tan(), and hypot() already available in the C standard library.

And hence, according to Gerald, they should not be particularly much harder to use, for a programmer, than the sin()’s, tan()’s and hypot()’s so readily available.

Gerald’s ingenuity also showed in the implementation of the vision, where he devised a comprehensive, yet simple, system of key-value pairs for parameterising a map projection, and the highly flexible PJ struct, storing run-time compiled versions of those key-value pairs, hence making a map projection function call, pj_fwd(PJ, point), as easy as a traditional function call like hypot(x,y)`.

While today, we may have more formally well defined metadata systems (most prominent the OGC WKT2 representation), nothing comes close being as easily readable (“human compatible”) as Gerald’s key-value system. This system in particular, and the PROJ system in general, was Gerald’s great gift to anyone using and/or communicating about geodata.

It is only reasonable to name a program, keeping an eye on the integrity of the PROJ system, in honour of Gerald.

So in honour, and hopefully also in the spirit, of Gerald Ian Evenden (1935–2016), this is the Geospatial Integrity Investigation Environment.