Oh.. sweet chaos!<br><br>The lack of a WKB-spec with Z (and M) ordinates seems to have triggered a bunch of WKB-flavours, such as<br>- OGR's "Two-and-a-half-D extensions for Simple Features"<br>- FDO's FGF-format<br>
- Postgis EWKB<br><br>I found the EWKB proposal here, but probably not the latest:<br><a href="http://postgis.refractions.net/pipermail/postgis-devel/2004-December/000710.html">http://postgis.refractions.net/pipermail/postgis-devel/2004-December/000710.html</a><br>
<br>As far as I can see, it is fairly similar in structure as the SQL/MM, except for the optional SRID. The object-type ID's are of course not the same.<br><br>In addition, SQL/MM specifies CircularString/CurvePolygon/CompundCurve etc aswell, would be nice to have these implemented in GEOS aswell (PostGIS has done some work here, not sure what)<br>
<br>I got two versions of the SQL/MM spec in PDF, the earliest (2nd edtion) dates from 2002. I'll send you the newest right away.<br><br>For now, I'll try to make a simple hack on the existing WkbReader.<br><br>Would be nice with a more united WKB-world...<br>
<br><br>-- Oyvind<br><br><br><br><br><br><div class="gmail_quote">On Thu, Aug 4, 2011 at 2:24 AM, Martin Davis <span dir="ltr"><<a href="mailto:mtnclimb@telus.net">mtnclimb@telus.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex;">
<u></u>
<div text="#000000" bgcolor="#ffffff">
The EWKB that JTS and GEOS implement is based on the PostGIS EWKB
specification (which predates the SQL/MM spec, I think.)<br>
<br>
I don't have a good reference for the PostGIS spec - it would be
nice if there was one online somewhere (hint, hint).<br>
<br>
It might be nice if JTS/GEOS supported the SQL/MM spec as well. Do
you have a reference available for the spec?<br>
<br>
Martin<div><div></div><div class="h5"><br>
<br>
On 8/3/2011 4:19 AM, Oyvind Idland wrote:
</div></div><blockquote type="cite"><div><div></div><div class="h5">Hello,<br>
<br>
i am trying to read WKB chunks based on the iso SQL/MM part3 spec.
However, this doesn't seem to work.<br>
<br>
From the WkbReader source code doc: <br>
"This implementation supports the extended WKB standard for
representing 3-dimensional coordinates. The presence of 3D
coordinates is signified by setting the high bit of the wkbType
word."<br>
<br>
Which extended WKB standard is being refered to here ?<br>
<br>
<br>
<br>
For example, In the SQL/MM spec, various point types are defined
as the following unsigned values (not hex):<br>
<br>
<wkbpoint> 1<br>
<wkbpointz> 3000001<br>
<wkbpointzm> 2000001<br>
<wkbpointm> 4000001<br>
<br>
However, in the WkbReader.cpp the following logic is used:<br>
<br>
int typeInt = dis.readInt();<br>
int geometryType = typeInt & 0xff;<br>
......<br>
bool hasZ = ((typeInt & 0x80000000) != 0);<br>
if (hasZ) inputDimension = 3;<br>
else inputDimension = 2; // doesn't handle M currently<br>
<br>
<br>
<br>
<br>
Is there any plans to implement support for SQL/MM ? (I can
volunteer for a patch, if desired)<br>
<br>
<br>
-- Oyvind<br>
<br>
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