Hello GRASS Community,
I’m having a problem that I’m hoping you can help me find the source of.
I think that either A) I am trying to use the v.generalize tool incorrectly, B) that my data has some sort of topological problem which I’m unaware of, or C) that there is a bug in v.generalize. The simplest way to describe what’s happening is that I am consistently unable to generalize a large group of contiguous polygons (African states most recently) without losing a large number of polygons from my data. I have tried a variety of different things, all without success, and now I’d like to ask if someone would be willing to verify that what I’m seeing isn’t a problem of my own creation. I’ve posted my data files at www.macrogis.net/africa, along with a before-and-after image of the specific problem I’ve encountered. I’m using GRASS v 6.4.1 which I downloaded from the main website 2 months ago. The commands I have used are the following:
v.in.ogr dsn=africa_clean.shp
v.clean tool=rmarea type=boundary thresh=200000000 in=africa_clean out=africa_clip
v.generalize type=boundary method=lang threshold=.015 look_ahead=11 in=africa_clip out=africa_general
Note: I know that I am removing small polygons with the v.clean operation. My concern is with the many missing contiguous polygons in the main part of the continent.
Thanks in advance for any help you can provide,
Roger
On Tue, Oct 25, 2011 at 11:07 PM, Roger André <randre@gmail.com> wrote:
Hello GRASS Community,
I'm having a problem that I'm hoping you can help me find the source of.
I think that either A) I am trying to use the v.generalize tool incorrectly,
B) that my data has some sort of topological problem which I'm unaware of,
or C) that there is a bug in v.generalize. The simplest way to describe
what's happening is that I am consistently unable to generalize a large
group of contiguous polygons (African states most recently) without losing a
large number of polygons from my data. I have tried a variety of different
things, all without success, and now I'd like to ask if someone would be
willing to verify that what I'm seeing isn't a problem of my own creation.
I've posted my data files at www.macrogis.net/africa, along with a
before-and-after image of the specific problem I've encountered. I'm using
GRASS v 6.4.1 which I downloaded from the main website 2 months ago.
This bug has been fixed in GRASS 6.4.2
Markus M
Hi Markus,
That’s good to know. Can you tell me the bug number? I’d like to review the details of it.
Thanks,
Roger
On Wed, Oct 26, 2011 at 12:23 AM, Markus Metz <markus.metz.giswork@googlemail.com> wrote:
On Tue, Oct 25, 2011 at 11:07 PM, Roger André <randre@gmail.com> wrote:
Hello GRASS Community,
I’m having a problem that I’m hoping you can help me find the source of.
I think that either A) I am trying to use the v.generalize tool incorrectly,
B) that my data has some sort of topological problem which I’m unaware of,
or C) that there is a bug in v.generalize. The simplest way to describe
what’s happening is that I am consistently unable to generalize a large
group of contiguous polygons (African states most recently) without losing a
large number of polygons from my data. I have tried a variety of different
things, all without success, and now I’d like to ask if someone would be
willing to verify that what I’m seeing isn’t a problem of my own creation.
I’ve posted my data files at www.macrogis.net/africa, along with a
before-and-after image of the specific problem I’ve encountered. I’m using
GRASS v 6.4.1 which I downloaded from the main website 2 months ago.
This bug has been fixed in GRASS 6.4.2
Markus M
Roger André wrote:
Hi Markus,
That's good to know. Can you tell me the bug number? I'd like to review
the details of it.
There is no bug number, at least I could not find a corresponding bug
number. There were a few complaints about v.generalize in the mailing
lists. In short, you are not the first one to discover this bug.
Additionally, v.generalize was randomly swapping area attributes. This
is also fixed.
Since you are asking about a bug number, are you interested in the
effects or the causes?
Markus M
Thanks,
Roger
--
On Wed, Oct 26, 2011 at 12:23 AM, Markus Metz
<markus.metz.giswork@googlemail.com> wrote:
On Tue, Oct 25, 2011 at 11:07 PM, Roger André <randre@gmail.com> wrote:
> Hello GRASS Community,
> I'm having a problem that I'm hoping you can help me find the source of.
> I think that either A) I am trying to use the v.generalize tool
> incorrectly,
> B) that my data has some sort of topological problem which I'm unaware
> of,
> or C) that there is a bug in v.generalize. The simplest way to describe
> what's happening is that I am consistently unable to generalize a large
> group of contiguous polygons (African states most recently) without
> losing a
> large number of polygons from my data. I have tried a variety of
> different
> things, all without success, and now I'd like to ask if someone would be
> willing to verify that what I'm seeing isn't a problem of my own
> creation.
> I've posted my data files at www.macrogis.net/africa, along with a
> before-and-after image of the specific problem I've encountered. I'm
> using
> GRASS v 6.4.1 which I downloaded from the main website 2 months ago.
This bug has been fixed in GRASS 6.4.2
Markus M
Ah, ok. The causes, please.
It’s a really powerful tool, and I would like to write some additional documentation on how to use it for generalizing and smoothing large polygon sets, but first I need to make sure that I can anticipate it’s behavior a little better. The area attribute swapping was something that I had noticed as well, but I figured that was just something to be expected.
Also, would it be helpful to have additional testers for some of these? I’m not using the raster tools at the moment, but am using the vector tools quite a bit (console only though).
Roger
On Wed, Oct 26, 2011 at 11:51 AM, Markus Metz <markus.metz.giswork@googlemail.com> wrote:
Roger André wrote:
Hi Markus,
That’s good to know. Can you tell me the bug number? I’d like to review
the details of it.
There is no bug number, at least I could not find a corresponding bug
number. There were a few complaints about v.generalize in the mailing
lists. In short, you are not the first one to discover this bug.
Additionally, v.generalize was randomly swapping area attributes. This
is also fixed.
Since you are asking about a bug number, are you interested in the
effects or the causes?
Markus M
Thanks,
Roger
On Wed, Oct 26, 2011 at 12:23 AM, Markus Metz
<markus.metz.giswork@googlemail.com> wrote:
On Tue, Oct 25, 2011 at 11:07 PM, Roger André <randre@gmail.com> wrote:
Hello GRASS Community,
I’m having a problem that I’m hoping you can help me find the source of.
I think that either A) I am trying to use the v.generalize tool
incorrectly,
B) that my data has some sort of topological problem which I’m unaware
of,
or C) that there is a bug in v.generalize. The simplest way to describe
what’s happening is that I am consistently unable to generalize a large
group of contiguous polygons (African states most recently) without
losing a
large number of polygons from my data. I have tried a variety of
different
things, all without success, and now I’d like to ask if someone would be
willing to verify that what I’m seeing isn’t a problem of my own
creation.
I’ve posted my data files at www.macrogis.net/africa, along with a
before-and-after image of the specific problem I’ve encountered. I’m
using
GRASS v 6.4.1 which I downloaded from the main website 2 months ago.
This bug has been fixed in GRASS 6.4.2
Markus M
Roger André wrote:
Ah, ok. The causes, please.
It's a really powerful tool, and I would like to write some additional
documentation on how to use it for generalizing and smoothing large polygon
sets, but first I need to make sure that I can anticipate it's behavior a
little better. The area attribute swapping was something that I had noticed
as well, but I figured that was just something to be expected.
Also, would it be helpful to have additional testers for some of these? I'm
not using the raster tools at the moment, but am using the vector tools
quite a bit (console only though).
Please use GRASS 6.4.2 for testing. A number of bugs present in 6.4.1
have been fixed in 6.4.2.
With regard to v.generalize, randomly swapping of area attributes was
a serious bug, this was by no means to be expected. This swapping
occurred because the original author used area ids instead of
categories to assign attributes to the smoothed vector. This is
within the logic of the GRASS vector model nonsense because area ids
are randomly assigned, area categories are instead fixed because
user-defined. The disappearance of polygons happened because smoothed
boundaries that violated vector topology were deleted, after that all
boundaries that were topologically incorrect. Boundaries are now only
smoothed/simplified if the modification does not violate vector
topology.
HTH,
Markus M
Roger
--
On Wed, Oct 26, 2011 at 11:51 AM, Markus Metz
<markus.metz.giswork@googlemail.com> wrote:
Roger André wrote:
> Hi Markus,
> That's good to know. Can you tell me the bug number? I'd like to
> review
> the details of it.
There is no bug number, at least I could not find a corresponding bug
number. There were a few complaints about v.generalize in the mailing
lists. In short, you are not the first one to discover this bug.
Additionally, v.generalize was randomly swapping area attributes. This
is also fixed.
Since you are asking about a bug number, are you interested in the
effects or the causes?
Markus M
> Thanks,
> Roger
> --
>
> On Wed, Oct 26, 2011 at 12:23 AM, Markus Metz
> <markus.metz.giswork@googlemail.com> wrote:
>>
>> On Tue, Oct 25, 2011 at 11:07 PM, Roger André <randre@gmail.com> wrote:
>> > Hello GRASS Community,
>> > I'm having a problem that I'm hoping you can help me find the source
>> > of.
>> > I think that either A) I am trying to use the v.generalize tool
>> > incorrectly,
>> > B) that my data has some sort of topological problem which I'm
>> > unaware
>> > of,
>> > or C) that there is a bug in v.generalize. The simplest way to
>> > describe
>> > what's happening is that I am consistently unable to generalize a
>> > large
>> > group of contiguous polygons (African states most recently) without
>> > losing a
>> > large number of polygons from my data. I have tried a variety of
>> > different
>> > things, all without success, and now I'd like to ask if someone would
>> > be
>> > willing to verify that what I'm seeing isn't a problem of my own
>> > creation.
>> > I've posted my data files at www.macrogis.net/africa, along with a
>> > before-and-after image of the specific problem I've encountered. I'm
>> > using
>> > GRASS v 6.4.1 which I downloaded from the main website 2 months ago.
>>
>> This bug has been fixed in GRASS 6.4.2
>>
>> Markus M
>
>