[GRASS-user] Trouble with v.in.ascii (x2) and v.out.ogr

[Paulo Marcondes]

2008/6/18 Hamish <hamish_b at yahoo.com>:
> Paulo Marcondes wrote:
>
>> I had issues while triyng to import an ASCII vector file,
>> that looks like this:
>>
>>  B 240 1
>>   333967.494 7610503.977
> ....
>>   334065.141 7610992.215
>>   334260.436 7610601.634
>>  1 1
>>
>> This should be a polygon that limits a very interesting
>> feature.
>
> missing a centroid?

I thought v.build would fix that for me.
So I have do add by hand? Also, where does a centroid goes, I mean,
any point inside the boundary, or some other specific place?

>> Also, I didn't manage to, while exporting to shape,
>> have the polygon filled. (the GRASS polygon fills OK)
>
> see example in v.out.ogr help page for areas -> shapefile.
>
>> Also, I had issues while trying to import an 815k lines
>> ASCII vector file,
...
> Not sure, do you need one coordinate per "P"?
> if only points, probably better to use "v.in.ascii format=point"
> and forget about all the formatting stuff, just give it a flat .csv file.
...
> you need to use v.in.ascii's "format=standard" if data is given in that form. "standard" format is not the default and should be renamed for GRASS 7 as the name is somewhat misleading.
> Did it used to be "format=grass" ?

Left it alone. r.in.xyz works great for my needs.
You are right with regards to the standard format, the name is a bit misleading.

>> When I imported (almost) the same ASCII file with r.in.xyz,
>> somewhere in the northern part of the raster I got a blank
>> E-W line, that I feel has something to do with that resolution
>> difference (99.97 vs 100m)
>
> probably that is correct, caused by a partial Moiré effect.
>
> adjust the res to be exactly 100 by expanding the bounds of the region with "g.region res=100 -a".

It works!
Raster loaded beautifully.

> grass uses the grid as cell bounds, not cell centers. so west= is the coord of the left of the leftest cell, and east= is the coord of the right of the rightest cell.
> ie 0,0 falls on a grid confluence, not a cell center.

Good to know. I thought otherwise.

>> So, what I tried to do was import as vector points to
>> interpolate and generate a nice raster.
>
> I've had success with that method + r.in.xyz, see
>  http://grass.osgeo.org/wiki/Marine_Science#Import_using_GMT
> tip: use a "n" map + r.univar to check that your alignment is correct.

Cool. Saves a lot of guessing.
-- 
Paulo Marcondes = PU1/PU2PIX
-22.915 -42.224 = GG86jc