<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Dear DAL,<div class=""><br class=""></div><div class="">At ESO we use DISTANCE( geometry, geometry ),</div><div class="">where geometry can be a point, a circle, a polygon, a union of polygons, a centroid, etc.<div class=""><div class=""><br class=""></div><div class="">The OGC standard: </div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>OpenGIS® Implementation Standard for Geographic information - Simple feature access - Part 1: Common architecture</div><div class=""><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>available at: <a href="http://portal.opengeospatial.org/files/?artifact_id=25355" class="">http://portal.opengeospatial.org/files/?artifact_id=25355</a></div></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>in the paragraph: 6.1.2.4 Methods that support spatial analysis</div><div class="">defines DISTANCE (along with, intersection, unions, etc).</div><div class=""><br class=""></div><div class="">No point in reinventing the wheel: let’s just take that definition and reuse it.</div><div class="">I quote it here:</div>
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<li class=""><p class=""><span style="font-size: 10.000000pt; font-family: 'Arial'; font-weight: 700" class="">Distance </span><span style="font-size: 10.000000pt; font-family: 'ArialMT'" class="">(anotherGeometry: Geometry):Double — Returns the shortest distance between any two Points in
the two geometric objects as calculated in the spatial reference system of </span><span style="font-size: 10.000000pt; font-family: 'Arial'; font-style: italic" class="">this </span><span style="font-size: 10.000000pt; font-family: 'ArialMT'" class="">geometric object. Because the
geometries are closed, it is possible to find a point on each geometric object involved, such that the distance
between these 2 points is the returned distance between their geometric objects. </span></p></li></ul></div></div></div><div class=""><div><br class=""></div><div>Regarding the grammar, something like this would do:</div><div><br class=""></div><div>DISTANCE <left_paren> <geometry_value_function> <comma> <geometry_value_function> <right_paren><br class=""><br class=""></div><div>where, though, I would ask to modify the current definition of <geometry_value_function>,</div><div>which is:</div><div><pre xmlns="http://www.w3.org/1999/xhtml" class=""><span class="verbline"><geometry_value_function> ::=
</span><span class="verbline"> <box>
</span><span class="verbline"> | <centroid>
</span><span class="verbline"> | <circle>
</span><span class="verbline"> | <point>
</span><span class="verbline"> | <polygon>
</span><span class="verbline"> | <user_defined_function></span></pre><div class="">probably removing the deprecated (is it still?) <box> </div><div class="">and adding:</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>| <union_of_geometries></div><div class=""><br class=""></div><div class="">with:</div><div class=""><br class=""></div><div class=""><pre xmlns="http://www.w3.org/1999/xhtml" class=""><span class="verbline"><union_of_geometries> ::=
</span><span class="verbline"> UNION <coord_sys> </span><left_paren></pre><pre xmlns="http://www.w3.org/1999/xhtml" class=""><span class="verbline"><span class="Apple-tab-span" style="white-space:pre"> </span><geometry_value_function></span></pre><pre xmlns="http://www.w3.org/1999/xhtml" class=""><span class="verbline"><span class="Apple-tab-span"> </span>{ </span><geometry_value_function> } ?</pre><pre xmlns="http://www.w3.org/1999/xhtml" class=""> <right_paren></pre></div></div><div>Alberto</div><div><br class=""></div><div><br class=""><blockquote type="cite" class=""><div class="">On 19. Feb 2020, at 16:14, Markus Demleitner <<a href="mailto:msdemlei@ari.uni-heidelberg.de" class="">msdemlei@ari.uni-heidelberg.de</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div class="">Dear DAL,<br class=""><br class="">Current ADQL says:<br class=""><br class=""> Functions like AREA, COORD1, COORD2 and DISTANCE accept a<br class=""> geometry and return a calculated numeric value.<br class=""><br class=""> The specification defines two versions of the DISTANCE function, one<br class=""> that accepts two geometries, and one that accepts four separate numeric<br class=""> values, both forms return a numeric value.<br class=""><br class="">Both statements would indicate that DISTANCE should accept general<br class="">geometries, i.e., including circles and polygons. <br class=""><br class="">The later definition of DISTANCE then says<br class=""><br class=""> The specification defines two versions of the DISTANCE function,<br class=""> one that accepts two POINT values, and a second that accepts four<br class=""> separate numeric values.<br class=""><br class="">-- which is clear enough, had it not been for the previous statement,<br class="">and the later statement<br class=""><br class=""> If the geometric arguments are expressed ...<br class=""><br class="">which might again be understood as saying the arguments can be more<br class="">general.<br class=""><br class="">Finally, the grammar says, for the geometry case:<br class=""><br class=""> DISTANCE <left_paren> <coord_value> <comma> <br class=""> <coord_value> <right_paren><br class=""><br class="">where<br class=""><br class=""> <coord_value> ::= <point> | <column_reference><br class=""><br class="">I *think* all this works out to say that over and above the grammar,<br class="">for distance there's the additional constraint that column_reference<br class="">must be POINT-typed.[1] <br class=""><br class="">Being general here is a pain in the neck (actually, that's why I ran<br class="">into this question). For one, you'll need to define distance<br class="">much more carefully for such geometries, and if (as I think we ought<br class="">to) we chose "minimum of distances of between all points in arg 1 and<br class="">arg 2", I doubt we'll see many correct implementations of that. Also<br class="">I'll want to map a lot of DISTANCE calls into contains(point,<br class="">circle) statements (because that's much easier on the query planner),<br class="">and that's a pain if one of the points could actually be, say, a<br class="">polygon.<br class=""><br class="">So... do we agree that DISTANCE only accept POINT-s?<br class=""><br class="">If so, I'd suggest to just drop the sentence:<br class=""><br class=""> Functions like AREA, COORD1, COORD2 and DISTANCE accept a<br class=""> geometry and return a calculated numeric value.<br class=""><br class="">Then change<br class=""><br class=""> The specification defines two versions of the DISTANCE function,<br class=""> one that accepts two geometries, and one that accepts four<br class=""> separate...<br class=""><br class="">to<br class=""><br class=""> This specification defines two versions of the DISTANCE function,<br class=""> one that accepts two POINTs, and one that accepts four<br class=""> separate...<br class=""><br class="">And then add in 4.2.16 in some appropriate location something like<br class=""><br class=""> Note that when <column reference>s[2] are passed into DISTANCE, the<br class=""> operation is only defined for POINT-typed values. Behaviour for<br class=""> other geometries is undefined at this point (but may be defined<br class=""> later).<br class=""><br class="">Would anyone veto a PR to this effect? Would anyone prefer something<br class="">completely different? Would anyone volunteer for doing the PR?<br class=""><br class=""> -- Markus<br class=""><br class="">[1] Incidentally, the grammar rules are incompatible with the<br class="">statement in the 4.2.16 that "[t]he DISTANCE function may be applied<br class="">to any expression that returns a geometric POINT value"; I see why it<br class="">was put in, but unless we fix the grammar, we should remove the<br class="">prose.<br class=""><br class="">[2] or <geometry_value_expression>s, depending on how you think about<br class="">[1]<br class=""></div></div></blockquote></div><br class=""></div></div></div></body></html>