[GRASS-user] Multiple to one question

[Adam Dershowitz, Ph.D., P.E.]

On Apr 14, 2009, at 4:06 AM, Moritz Lennert wrote:

> On 14/04/09 08:37, Vincent Bain wrote:
>> Hello Adam,
>> maybe another solution in this case would be a set of 2 tables :
>> * one linking to the geometry, that is containing nothing but cat
>> values,
>> * another one, containing a cat column (related to the "geometric"
>> table) and different data columns corresponding to your sampling.
>
> I think that if all you want is calculate some means or similar  
> across dates and then display the results, Vincent's solution is the  
> easiest.
>
> But you could also use layers [1]:
>
> layer 1 = January round of sampling
> layer 2 = February round of sampling
> etc.
>
> You would have to give each point a category value in each layer (cf  
> v.category) and then either create separate tables for each period  
> linking each to one of the layers or at least create some obvious  
> cat values (i.e. 100s for January, 200s for February, etc) and link  
> on single table to all the layers, but with different cat values in  
> each layer.
>
>
> Moritz
>
> [1] See "Vector object categories and attribute management" on http://grass.osgeo.org/grass64/manuals/html64_user/vectorintro.html 
>  for a quick introduction

Thanks,

But, the problem with both of these approaches, columns, and layers,  
(Vincent or Moritz version) is that I don't have consistent times for  
each site.  So, at site A I might have 5 samples, once a month and at  
site B I have 2 samples, one each year, and site C I have a few spread  
over a few years.
So both of those approaches essentially need to have a column, or  
layer, for each possible time of sampling.  But that is not really  
appropriate for the quasi-random times of the samples.


>
>
>> Does this help ?
>> VB
>> Le lundi 13 avril 2009 à 14:23 -0700, Adam Dershowitz a écrit :
>>> I am trying to set up a new project in Grass, and I have a  
>>> question  about the best approach.
>>> I have different vector locations, and at each one there were  
>>> multiple  samples taken.  At the moment I have each sample as a  
>>> row in a data  base.
>>> My question is how best to put this data into a set of vector  
>>> points.
>>> I believe that I can do it in either of two ways (of not others).
>>> 1)  I can create a vector point at each location, then I think  
>>> that I  can have multiple cats for that object.  So I think I can  
>>> do cat=1,3,6  for a given location.
>>> Will that work OK?
>>> 2)  I can just create different vector objects, that happen to be  
>>> at  the identical location, and have each one point to a different  
>>> cat.
>>>
>>> If the above is not clear, here is a bit more detailed example.
>>> At location A there was a sample collected on 1/1 with a value of  
>>> 2.1,  on 2/2 with a value of 2.2 and on 3/3 with a value of 3.3
>>>
>>> The above data is already 3 rows in a database.
>>>
>>> I want to be able to display data about point A (say, average  
>>> value or  things like that).  Should I just create a vector point  
>>> A and then do  cat=1,2,3 or should I create 3 different vector  
>>> points at A, each one  having a different cat?
>>>
>>> Any guidance about the benefits or limitations each approach (or  
>>> any  other approach to consider) would be greatly appreciated.
>>>
>>> Thanks,
>>>
>>> --Adam
>>>
>>>
>>>
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