[Manifold-l] On screen digitizing of curves

[Springfield Harrison]

Hello Simon:

         Thank you.  From what I've learned so far, I'm not sure why they 
need arcs on the corners.  I thought it was to reduce the number of record 
entries in the related table but extra segments to not create extra 
records, unless one uses Explode.  Tight digitizing would seem to be fine, 
so I'll propose that.

         I'm not sure if the arc/curve approach is feasible, even with the 
right tools, as with roads there are very few curves with a consistent 
radius throughout.

         As Pat Waggaman pointed out, arcs, poorly defined, may be more 
erroneous than good OSD.  And certainly more fiddly to generate.

         It might be a bit more streamlined with a railroad but I think 
they use spirals in and out of the turn, too (to reduce side loading on the 
rails (?)).  I think they may be making a difficult job out of a simple 
one.  Their own data is not "curved".

         OSD is on screen digitizing (heads up digitizing) over vector data 
or an orthophoto.

         Thanks for the great feedback, cheers . . .

At 06/11/2007 10:28 PM Tuesday, Simon Greener (SpatialDB Advisor) wrote:
>Yes, ESRI geodatabases have curves (as does Oracle Locator), but over time
>the curves in geodatabases can lose their radius as snapping occurs. Get
>your potential customer to search the ESRI forums about these problems.
>(Though they might be fixed in ArcGIS 9.2.)
>
>And, yes, Manifold cannot create or edit data with curves. Manifold
>strokes any curved line segments in an Oracle Locator database.
>
>Pat Waggaman's observations about stroking curves are correct: but I would
>say get someone to write you a tool for 8.0 that asks for three points
>that define a circle - start and end point of the curve and either the
>centre of the circle or another point on the circumference - and then
>programmically creates a stroked linestring using a user entered
>arc-to-chord separation (for cadastral data a separation of 3mm is
>sufficient but you could reduce it to 1mm). The cost of writing this tool
>+ Manifold GIS would be far less than purchasing ArcGIS.
>
>I have the COGO code to do all this for Oracle and could port it to
>VBScript and Manifold quite easily but I would want payment for doing so
>as I work for myself!
>
>BTW what is OSD in your email?
>
>regards
>Simon
>On Wed, 07 Nov 2007 08:41:20 +1100, Springfield Harrison
><stellargps at shaw.ca> wrote:
>
>>          From the forum:
>>
>>Hello:
>>
>>A potential client needs on screen digitizing of roads from an orthophoto
>>but the curves cannot be line segments. Apparently the ESRI Geodatabase
>>into which these data will go can define curves with a start, end and
>>radius.
>>
>>This may be so but how can OSD be used to create curves in Manifold, or
>>anything else for that matter. I think OSD can only create straight
>>segments joining mouse clicks. Even stream digitizing is a series of very
>>closely spaced dots, I think.
>>
>>Can this actually be done as required by the proponent using OSD?
>>
>>Thanks very much, Springfield
>
>                            Spring Harrison
>                                       Stellar GPS & Mapping
>                                 103 - 9800 McDonald Park Road
>                                        Sidney, B. C. Canada
>
>                                          www.StellarGPS.ca
>
>                                  Voice, 24 hr: (250) 655-0764
>                                     Toll free: (888) 655-0764
>                                         Fax: (250) 654-0049
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://www.directionsmedia.net/pipermail/manifold-l/attachments/20071106/ebbdbb88/attachment.html