[GRASS-user] How to create an hull / area with v.in.ascii

[Philipp Steigenberger]

Martin Landa schrieb:
> Hi,
>
> 2008/2/4, Philipp Steigenberger <userlist at online.de>:
>   
>> I have  cross-profiles of a river and want to create a terrainmodel.
>> To interpolate only there, where points are, I want to create a hull.
>> v.hull doesn't work, cause - how to explain... - imagine, the river has
>> the form of the letter 'S' with v.hull I get a form whisch is almost
>> like a 'D'.
>>
>> Therfore I extracte all the lines where I have the points of the
>> right(r) /left(l) side of the cross-profile
>>
>> I sort them like
>> cat   name
>> 1         l 1
>> 2         l 2
>> 3         l 3
>> 4         l 4
>> 5         r 4
>> 6         r 3
>> 7         r 2
>> 8         r 1
>>
>> so it looks like:
>>
>> 1 4417744.050 5363469.320 461.10400 0.20000 P1(li)
>> 2 4417723.140 5363269.800 461.83000 0.40000 P1(left)
>> 3 4417716.890 5363068.970 461.40100 0.60000 P1(left)
>> 4 4417705.220 5362867.590 461.93600 0.80000 P1(left)
>> 354 4403074.030 5335808.330 559.44700 34.00000 P2(right)
>> 355 4402974.470 5335628.060 559.60400 34.20000 P2(right)
>> 356 4402876.360 5335452.300 560.11700 34.40000 P2(right)
>> 357 4402779.380 5335277.370 561.11800 34.60000 P2(right)
>>
>> I add
>> A 357 1 in the first line and
>> 1 1         in the last line
>>
>> Now I want to import this as an area:
>>
>> cat wertach.asc | v.in.ascii --o output=wertach skip=1 -z z=4 cat=1 x=2
>> y=3 colum='cat int, x double, y double, z double, name01 varchar(20),
>> name02 varchar(20)' fs=' '
>>
>> and get
>>
>> Scanning input for column types...
>> Maximum input row length: 54
>> Maximum number of columns: 6
>> Minimum number of columns: 2
>> ERROR: y column number > minimum last column number
>>        (incorrect field separator?)
>>
>> so I delete the last line and get
>>
>> Scanning input for column types...
>> Maximum input row length: 54
>> Maximum number of columns: 6
>> Minimum number of columns: 6
>> WARNING: Column number 5 defined as string has double values
>> Importing points...
>> Populating table...
>> Building topology for vector map <wertach>...
>> 357 primitives registered
>> Building areas:  100%
>> 0 areas built
>> 0 isles built
>> Attaching islands:
>> Attaching centroids:  100%
>> Topology was built
>> Number of nodes     :   357
>> Number of primitives:   357
>> Number of points    :   357
>> Number of lines     :   0
>> Number of boundaries:   0
>> Number of centroids :   0
>> Number of areas     :   0
>> Number of isles     :   0
>> v.in.ascii complete.
>>
>> NO AREA :o(
>>
>> If I try
>> B 357 1 for a boundary I get the same
>>
>> Scanning input for column types...
>> Maximum input row length: 54
>> Maximum number of columns: 6
>> Minimum number of columns: 6
>> WARNING: Column number 5 defined as string has double values
>> Importing points...
>> Populating table...
>> Building topology for vector map <wertach>...
>> 357 primitives registered
>> Building areas:  100%
>> 0 areas built
>> 0 isles built
>> Attaching islands:
>> Attaching centroids:  100%
>> Topology was built
>> Number of nodes     :   357
>> Number of primitives:   357
>> Number of points    :   357
>> Number of lines     :   0
>> Number of boundaries:   0
>> Number of centroids :   0
>> Number of areas     :   0
>> Number of isles     :   0
>> v.in.ascii complete.
>>
>> NO BOUNDARY :o(
>>
>> what went wrong? How to bulid an area? Do I need a centroid? How to get it?
>> Or do I only need x and y -values to create the area?
>>     
>
> Please, take a look at v.in.ascii manual page where GRASS ASCII format
> is described. E.g.
>
> B  2 1
>  595521.680672 4925244.201681
>  593757.983193 4917668.319328
>  1     1
> B  5 1
>  593757.983193 4917668.319328
>  593757.983193 4917668.319328
>  603618.655462 4915223.193277
>  606344.369748 4923801.176471
>  595521.680672 4925244.201681
>  1     1
> B  4 1
>  595521.680672 4925244.201681
>  589468.991597 4926727.310924
>  587945.798319 4918670.420168
>  593757.983193 4917668.319328
>  1     2
> C  1 1
>  599449.915966 4920554.369748
>  1     3
> C  1 1
>  591072.352941 4922077.563025
>  1     4
>
> defines three boundaries (category 1,2) and two centroids (cat 3,4).
>
> cat input.txt | v.in.ascii out=xx for=standard -n --o
>
> Note that you need to specify input format (default format is 'points'
> not 'standard'). After import you can also add missing centroids using
> v.centroids module.
>
> Martin
>
>   
Martin,
I always use the help and man pages when I work within GRASS, but do not 
understand everything...
I also have the new Neteler & Mitasova...

Now I know which syntax I need for ponts and which for standard (lines etc.)
Is it is important to have leading blanks in front of the points? Or is 
it just for clarity?

B  5 1
 593757.983193 4917668.319328
 593757.983193 4917668.319328
 603618.655462 4915223.193277
 606344.369748 4923801.176471
 595521.680672 4925244.201681
 2     3


For my own clarity

B for Boundary, L for Lin,e A for Area, C for Centroid, and P for Point
5 is the number of points
1 ??? Neteler & Mitasova describe "1 for a single category" - what does this mean? 
2 is the layer number
3 is the category ID 

In your example the first and second boundary have the same cat ID. Why?

More and more I understand this vektor-thing in GRASS - but I still need some time ;o)

Thanks a lot

om shantih
Philipp



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