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Hello Stefani<br>
<br>
Accuracy depends if the coordinate operation involves datum shift or
not. The ISO 19111 international standard (<i>Spatial Referencing by
Coordinates</i>) defines two terms - <i>transformation</i> or <i>conversion</i>
- depending on the above.<br>
<br>
If there is a datum shift (<i>coordinate <u>transformation</u></i>),
the main cause of inaccuracy does not depend on the software
(assuming there is no major bug). The accuracy rather depends on the
way the datum shift has been defined in the real world. This
accuracy is recorded in the EPSG database on a case-by-case basis.
The accuracy reported by EPSG is often 1 meter, sometime less,
sometime more. If an application needs this information, then the
application may need a library connected to the EPSG database or
something equivalent. Alternatively, if the application only need a
limited set of coordinate operations, you may get this information
manually from <a class="moz-txt-link-freetext" href="http://epsg-registry.org/">http://epsg-registry.org/</a><br>
<br>
If there is no datum shift (<i>coordinate </i><i><u>conversion</u></i>),
then the accuracy is software-dependent. It usually depends on
rounding errors and approximations used in the projection
algorithms. To my knowledge, most major libraries have a good
precision (1 centimeter or better) if the coordinates are inside the
projection domain of validity. Those domains of validity can also be
found in the EPSG database.<br>
<br>
To test the accuracy of a software, the EPSG authors created a tests
suite: the <i>Geospatial Integrity of Geoscience Software</i>
(GIGS) tests (<a class="moz-txt-link-freetext" href="http://info.ogp.org.uk/geomatics/gigs.html">http://info.ogp.org.uk/geomatics/gigs.html</a>). Those
tests are defined as Microsoft Excel files, but some of them have
been implemented in the Java language in the GeoAPI conformance
module (<a class="moz-txt-link-freetext" href="http://www.geoapi.org/geoapi-conformance/index.html">http://www.geoapi.org/geoapi-conformance/index.html</a>). It
does not means that the library must be written in Java - we can
write wrappers using JNI. We have done exactly that for the Proj.4
library, which allowed us to run some GIGS tests on Proj.4. If they
were some volunteers for writing JNI/GeoAPI wrappers around CS-Map,
it would be possible to run some GIGS tests on CS-Map.<br>
<br>
Martin<br>
<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">Le 14/08/14 10:43, Stefani Paolo a
écrit :<br>
</div>
<blockquote
cite="mid:86BF8ABC-7971-45A4-9CBA-6F904740308A@idscorporation.com"
type="cite">
<pre wrap="">Hello,
I am in charge of the design of a software tool that will collect survey data and integrate it in a database and am thinking of using CS-Map to handle the transformation from local to global coordinate systems and I have a question that I have not been able to answer looking at the CS-Map documentation that I have found on the internet.
The question is the following: I would like to have some information regarding the numerical accuracy of the CS-Map transformation engine when used to convert between different coordinate systems. I do understand that CS-Map is an open source and commonly used transformation engine but, due to software safety requirements, I do need to have evidence about the accuracy figures that CS-Map provides, in my case when transforming from a local to a global coordinate system.
Thanks in advance and best regards,
Paolo Stefani
</pre>
</blockquote>
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