[postgis-users] Linear referencing capability

[David William Bitner]

On Thu, Aug 23, 2012 at 11:24 AM, Melpati, Muni <
Muni.Melpati at dot.state.fl.us> wrote:

> In a shapefile, especially routes, you can have user defined measures
> (m-values, usually in miles), they might not be same when you measure the
> two dimenstional line, from  start to end vertices of any feature. These
> shapefiles would have begin and end post fields as attributes.****
>
> It is not the case for any shapefiles with line types since two
> dimensional measures deviate from real distance from point a to point b.
> Moreover they would not be in miles.****
>
> I was asking if I import a shapefile of “polyline M” into PostGIS would I
> be able to get measure in miles given a point or would I be able to get
> points given a measure in miles? Orelse there is different mechanism in
> PostGIS
>

If your shapefile has an M value and you use shp2pgsql to import it into
PostGIS, it will still have the M values intact. ogr2ogr and some other
tools do not carry forward the M value.


> ****
>
> to the same job. If so how it is done. I know there are few methods to
> retrieve a mile point or a measure give a point in PostGIS. Doesn’t this
> require calibrating the route, first, like I found out in this link (
> http://www.faunalia.com/lrs). Sorry for not being very clear in my
> previous question. I thought people might have confounded this situation
> and can easily understand it. Please let me know if still do not understand
> or help me if you can.
>
You can use all the linear referencing tools on this data using that
measure value. See
http://postgis.org/documentation/manual-2.0/reference.html#Linear_Referencing



> ****
>
> ** **
>
> Date: Tue, 21 Aug 2012 21:12:04 -0400****
>
> From: "Paragon Corporation" <lr at pcorp.us>****
>
> Subject: Re: [postgis-users] created linear referencing system****
>
> To: "'PostGIS Users Discussion'"****
>
>       <postgis-users at postgis.refractions.net>****
>
> Message-ID: <527D56A990434161A53D6CA92B3D9ED9 at O>****
>
> Content-Type: text/plain; charset="us-ascii"****
>
> ** **
>
> Muni,****
>
> ****
>
> Not sure what you are asking and maybe others have a similar problem****
>
> understanding.  That might be why you haven't received an answer.****
>
> ****
>
> What do you mean by linear reference capable?  All spatial data that is of
> ****
>
> linestrings can be linearly referenced.  Are you talking about a specific*
> ***
>
> tool you are using?****
>
> ****
>
> when you load your data from shape file to PostGIS, the data is still the*
> ***
>
> same.  If it had linestrings before, it should still have linestrings.****
>
> ** **
>
>   _____  ****
>
> ** **
>
> From: postgis-users-bounces at postgis.refractions.net****
>
> [mailto:postgis-users-bounces at postgis.refractions.net<postgis-users-bounces at postgis.refractions.net>]
> On Behalf Of Melpati,****
>
> Muni****
>
> Sent: Tuesday, August 21, 2012 4:07 PM****
>
> To: postgis-users at postgis.refractions.net****
>
> Subject: [postgis-users] created linear referencing system****
>
> ** **
>
> ** **
>
> ** **
>
> Hi,****
>
> ** **
>
> I have asked this question before and could not get straight answer. I have
> ****
>
> a shape file which Linear reference capable. How to import such data?****
>
> ** **
>
> If I load the data using shape file loader, would the imported data is****
>
> linear reference capable. If not how to recreate linear referencing system
> ****
>
> on imported data?****
>
> ** **
>
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-- 
************************************
David William Bitner
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