[GRASS-user] linear referencing system - has anyone used it?

[Trevor Wiens]

On Wed, 14 Mar 2007 12:37:28 -0800
Lindsay Mico wrote:

> I posted a question a few weeks ago about the linear referencing system.  
> Has anyone actually used it to make new maps from field data?  Unfortunately 
> the developer of this function (Radim Blazek) no longer works on Grass.  
> Below is a copy of my original question.
> 
> Thanks and cheers.
> 
> 
> Fellow GRASS users,
> 
> I would like to build a new point data layer from a large database of stream
> surveys which have 2 pieces of spatial info:
> 
> 1) an LLID number for that stream
> 2) distance from the start of that stream

I've only used v.lrs.segment with single line segments, not networks
of lines. For this I passed this type of information formated as:

P stoptext catnum offset

in a text file and piped it to the command.

> 
> Based on what I have seen, I would use the linear referencing system
> modules.  I am not sure if I need to build a new reference layer as I have a
> stream layer with the LLID info already in it.  Additionally, I could not
> find an example of how v.lrs.segment works in practice.  I have attempted to
> summarize things as I understand it to help make it easier to answer my
> questions.  As I understand it the input parameters for v.lrs.segment would
> be as follows:
> 
> 1) input= the stream layer with the associated LLID info
> 2) output = the name of the output layer
> 3) llayer = whether it is a point or line (is it 1 for line and 0 for
> point?)

Please refer to the GRASS vector intro for details on layers within
vector files. Essentially, unless you are messing with this "feature"
it will always be 1.

> 4) rsdriver = I don't know what this means

dbf, pgsql, sqlite, etc

> 5) rsdatabase = the location of the file with the LLID # and distance

name of database, for example name of sql database. 

> 6) rstable = the name of the file which has the LLID number and distance?

table name

> will it automatically add in the other data in the database?  Or do I do
> that later using a spreadsheet program on the .dbf
> 
> As I am still learning how to do this, I expect I will have more questions
> in the future.  Hopefully this will be of use to others as well.  Many
> thanks in advance.  Cheers.
> 

It is useful to read through all the material in the tutorial if you
haven't already done so.

T
-- 
Trevor Wiens 
twiens at interbaun.com

The significant problems that we face cannot be solved at the same 
level of thinking we were at when we created them. 
(Albert Einstein)