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From "Martin Desruisseaux (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (SIS-362) Is there a way to convert geoidal altitudes to ellipsoidal altitudes?
Date Tue, 13 Jun 2017 12:56:00 GMT

    [ https://issues.apache.org/jira/browse/SIS-362?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16047844#comment-16047844
] 

Martin Desruisseaux commented on SIS-362:
-----------------------------------------

The code performing the _"Geographic3D to Geographic2D + gravity-related height"_ transformation
(EPSG:9635) has not yet been ported to Apache SIS. This is the task of SIS-283. However in
the meantime, some code exists in Geotk for this purpose. The [Geotk project|http://www.geotoolkit.org]
is built on top of Apache SIS and provides a temporary home for some functionalities not yet
ported to SIS. The [download page|http://www.geotoolkit.org/download.html] contains some instructions
for linking the Geotk extensions to Apache SIS referencing module (forget the Log4J part if
you do not use this framework - it is only an example). Then you can use this code (note that
it has no explicit reference to Geotk; its extensions will be used automatically):

{code:java}
import java.text.ParseException;
import org.opengis.geometry.DirectPosition;
import org.opengis.referencing.transform.MathTransform;
import org.apache.sis.geometry.GeneralDirectPosition;
import org.apache.sis.io.wkt.WKTFormat;

public final class Test {
    public static void main(String[] args) throws ParseException {
        final WKTFormat parser = new WKTFormat(null, null);
        final MathTransform mt = (MathTransform) parser.parseObject("Param_MT[\"Ellipsoid_To_Geoid\"]");
        DirectPosition before = new GeneralDirectPosition(new double[] {45, 45, 1000});  //
(lon, lat, height)
        DirectPosition after = mt.transform(before, null);
        System.out.println("Before transformation: " + before);
        System.out.println("After transformation: " + after);
    }
}
{code}

The above code is unconvenient and does not fit naturally in the usual way to use Apache SIS.
Furthermore the above is not NAD88, but a worldwide _"WGS84 ellipsoid to WGS84 geoid"_ model
based on a {{EGM180.nor}} data file. All those problems will need to be fixed when we will
port this transformation to SIS.

> Is there a way to convert geoidal altitudes to ellipsoidal altitudes?
> ---------------------------------------------------------------------
>
>                 Key: SIS-362
>                 URL: https://issues.apache.org/jira/browse/SIS-362
>             Project: Spatial Information Systems
>          Issue Type: Wish
>          Components: Referencing
>            Reporter: Pranava Shashank
>
> Hi, 
> I'm unable to find a suitable way/method to convert/transform an altitude in WGS84 reference
system to an altitude in NAVD88 reference system at a given point (ltitude, longitude) or
vice versa. 
> Can you please provide a complete example to achieve the above?
> I have read somewhere that epsg method 9635 would achieve the above but i could not find
one method in apache sis.



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