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Hi Darryl & list.<br>
I have not looked at the Spatialite discussion, and may not have
time to do so right now - so yes, there may be a viewpoint that I
have missed.<br>
But my comment is quite simply that it is the programmers duty to
write code that does the job correctly, without the user hitting
problematic caveats.<br>
<br>
I know this sounds naively idealistic, but maybe I have been spoilt.<br>
<br>
My first exposure to GIS was the mainframe based SICAD - which had
both full topology, and a scripting language. At user level you
could simply walk through the data structue, and ask questions like
"what area features lie on each side of my current line feature that
I am querying?" The rendering was pretty good, even though we are
talking mainframe based technology during the period 1984 to 1989.<br>
<br>
I then went on to Genamap which is/was UNIX/Linux based and has
exactly the same, and more, capabilities (than SICAD had). I have
used Genamap since 1990 (yep, >21 years), and enjoyed full
freedom from having to split geometries etc. It renders with its own
java based methods, and also SVG.<br>
<br>
So no, I can't agree with the point of view that speed comes before
data integrity, and sit and wonder why the old programmers got it
right, and the new ones find reason not to do it the (programmatic)
difficult way.<br>
<br>
my 2c,<br>
Zoltan<br>
[and sorry about the history lesson]<br>
PS: Property survey data is notoriously "wrong" [ie: full of
slivers, overlaps etc] and is a prime candidate for exactly the
opposite of Darryls example: Put the documented surveyed coordinates
as attributes, and then create a "best possible" topologically
correct map, so that the user is able to make queries on adjoining
properties through the topology rather than through spatial
mechanisms.<br>
At this point, luckily, I have run out of 2c coins :-)<br>
<br>
<br>
<br>
On 2011/07/22 14:53, Darryl Bailey wrote:
<blockquote
cite="mid:CANF9=bP+_KO42Xqu_RX6EhgLi9YFep26D71VzJXmSfVxcc7uSg@mail.gmail.com"
type="cite">
<div>Hi,</div>
<div> </div>
<div>I've been thinking along simialir lines with property survey
data. I figured that its not really the GIS program's task to
do this, but the underlying file or data structure. The way i
see it is that instead of having the coords "hard coded" for the
sewer lines, it would be preferable that the sewer lines coords
reference those coords as defined by the manholes. So if you
change the manholes' coords then the sewer line is automatically
updated.</div>
<div> </div>
<div>I thought this may be catered for by SpatiaLite and put the
query to their user list and got quite a good response.
Basically this sort of setup (strict topology) hampers
processing speed(and viewing speed for that matter), which is
what the majority of the end product of a GIS is used
for. This got me thinking - keep the topological data as
attribute data and then create the spatial data as and when
required so that the coords are hard coded into the actual
spatial file/dataset. Maybe a QGis plugin could be created to
do this.</div>
<div> </div>
<div>Here is a link to the SpatiaLite disscussion <a
moz-do-not-send="true"
href="http://groups.google.com/group/spatialite-users/browse_thread/thread/39a355fab8202081/3883d30053e35d07#3883d30053e35d07">http://groups.google.com/group/spatialite-users/browse_thread/thread/39a355fab8202081/3883d30053e35d07#3883d30053e35d07</a></div>
<div> </div>
<div>Regards</div>
<div>Darryl Bailey </div>
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<br>
<br>
<pre class="moz-signature" cols="72">--
===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
P.O. Box 7, Muizenberg 7950, South Africa.
65 Main Road, Muizenberg 7945
Western Cape, South Africa.
34° 6'16.35"S 18°28'5.62"E
Tel: +27-21-7884897 Mobile: +27-83-6004028
Fax: +27-86-6115323 <a class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
===========================================</pre>
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