[GRASS-user] Multiple to one question

[Moritz Lennert]

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

> 
> 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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> 
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