[postgis-users] Looking for documentation on measures
strk at refractions.net
strk at refractions.net
Tue Oct 4 00:55:10 PDT 2005
Chris, some No-Nos from a quick read and a build test:
- addLastPoint is declared to return LWLINE, but
pglwgeom_serialize() used in return produces a PG_LWGEOM intead
- on line 878 and 881 you assign a PGLWGEOM to an LWGEOM
- on line 943 you don't use Postgresql macros for the return
Some generic things:
- Some warnings are due to non-correct const usage in lwgeom lib
(like lwgeom_getnumgeometries not taking a const arg)
- all LW* objects can be upcast to LWGEOM, if you make all LW* returning
functions actually return LWGEOM there'll be no need to use cast
on return type (see first two compiler warnings)
- it is often preferrable to work on deserialized geoms rather then
serialized ones, mainly for reuse but sometimes for speed as well
- make_lwpoint2d() returns allocated memory, should be manually freed
On Mon, Oct 03, 2005 at 11:44:29PM -0400, Christoph Spoerri wrote:
> Hi there,
> attached is code for some LRS functions that I implemented in my spare time.
> The cover the basics and include:
> - create M values based on line length or the percentage along line
> - return a measure for a given point (point doesn't need to be on LRS/line)
> - return point given a measure
> - return a line given two measure (start and end)
> Other functions I was think of implementing:
> - create M values based on user input (start and end M)
> - create M values based on user input (array of M values)
> - return line given measure values and an offset value; this one would
> calculate a new line and offset from the original
> - recalculate M values based on ???
> - others ???
> the attached code has a couple more explanation in the header.
> In case somebody is new the LRS or is wondering how I implemented the LRS with
> the M value of the postgis LWGEOM, please take a look at
> http://www.gisgeek.com/lrs/. Bill Wheaton was so nice and started a tutorial
> for LRS with some examples.
> Note: I'm not an expert C coder, therefore the code still throws some compile
> errors. Yet, so far they didn't lead to any crashes :) Also, if a C expert
> sees some big No-No, please let me know.
> Enjoy and let me know what you think or find. If you like what you see and
> would like any additional enhancements, feel free to drop me a note. I would
> love to add some more functionality.
> On Monday 03 October 2005 15:19, Chris Matheson wrote:
> > Hello Everyone,
> > I am new to PostGIS, and I am looking for documentation related to
> > "measures" and "linear referencing" (particularly interested in
> > functions). Hopefuly documentation exists, if so would someone please
> > be kind enough to send me a reference.
> > Chris M.
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