[postgis-users] srid

[Paragon Corporation]

Bob,

I find it very interesting what you are trying to do.  I've always thought
that the whole spatial database model can be usefully applied to other
domains besides geography.  It is nice to see someone trying to do that.

As far as ST_Transform goes,  still not quite clear how it plays into your
problem.  To be honest - I haven't really delved into the guts of what
assumptions proj4 makes about geometry models except that it was founded on
dealing with geography data.

The whole Transformation infrastructure of PostGIS is based on proj4 and
really the proj4text in the spatial_ref_sys as far as I know is all that is
used by the PostGIS ST_Transform (srid for lookup).

I would imagine to expand its use for other domains in a meaningful way we
would probably have to replace the field proj4text in spatial_ref_sys tables

with  - projmodeltext,  projmodel

Where projmodel would define a library used for doing the spatial transforms
(in current case - they would all be filled in with 'proj4') , projmodeltext
would be the transformation params that the model needs 
and then any spatial reference systems based on the same function model can
be transformed in between each other.

Note: PostGIS actually deviates from the standard OGC spatial_ref_sys
structure in that in the plain vanilla OGC Spatial_ref_sys,  proj4text field
doesn't exist.


Just my 2 cents,
Regina


-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net] On Behalf Of Bob
Pawley
Sent: Monday, May 26, 2008 9:34 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] srid

That is what I am attempting.

I know of Visio. My thought of using Postgis is to, if possible, use the
functions that Postgis provides. In the very long range I was also
considering the 3D aspect of Postgis.

Your suggestion of using "boxes", presumably to provide reference points is
my backup method, if ST_Transform isn't applicable.

I would still like to consider ST_Transform as it appears to be a more
flexible approach.

Bob


----- Original Message -----
From: "Chris Hermansen" <chris.hermansen at timberline.ca>
To: "PostGIS Users Discussion" <postgis-users at postgis.refractions.net>
Sent: Monday, May 26, 2008 6:05 PM
Subject: Re: [postgis-users] srid


> Or, in another direction... Bob, if your "geometrical data" is meant to
> be something like a "data flow diagram" or a "process diagram", you can
> surely do that with PostGIS.
>
> Doubtless you must be aware of tools like Visio (in Windoze) or Dia (in
> Linux or Windoze) that are made for drawing diagrams like "data flow",
> but nevertheless you've decided to put your data into PostGIS instead.
>
> Then you probably want to make some "boxes" in your process diagram
> appear above, below, to the right of, or to the left of, other boxes.
>
> To do that, you would need to define some kind of partial order on the
> boxes (this box is to the right of that box, etc).  This sounds like a
> topological sort to me.
>
> Presumably you could turn that topological ordering into some set of
> offsets that could be applied to compute coordinates of each box.
>
> is that where you're trying to end up?
>
> Andy Anderson wrote:
>> On May 26, 2008, at 3:06 PM, Bob Pawley wrote:
>>
>>> However, I attempting to interpret functions made for geographic data
>>> to use with geometric data.
>>>
>>> I have PostgreSQL tables which represent engineering processes.
>>>
>>> I want to display that data in a graphical form - hopefully using
>>> Postgis - - - if I can translate the functions (or the Postgis
>>> concept) into a form that I can use.
>>
>> Hmmm... if all you want to do is display X-Y data, I would suggest
>> using geographic coordinates, e.g. SRID = 4326 (WGS84 datum), which
>> most programs will display by default with X and Y rectilinear.
>>
>> However, you earlier said you wanted to use ST_Transform(geometry,
>> integer), which implies you want to switch between different geographies.
>>
>> So it sounds like you need to pick a particular projection for your work.
>>
>> Is your geography spherical or spheroidal? If so, you might want to
>> define your own datum. If not, you'll need to use a projection to a
>> flat surface. What's more important, that it be conformal
>> (equiangular) or equal area or that it preserve distance in one
>> direction?
>>
>> -- Andy
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>
>
> -- 
> Regards,
>
> Chris Hermansen         mailto:chris.hermansen at timberline.ca
> tel+1.604.714.2878 . fax+1.604.733.0631 . mob+1.778.232.0644
> Timberline Natural Resource Group . http://www.timberline.ca
> 401 . 958 West 8th Avenue  . Vancouver BC . Canada . V5Z 1E5
>
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