[GRASS-user] v.generalize issues

GRASS GRASS user
,
1

I’m a brand new user to GIS - my goal right now is to heavily simplify Tiger 2010 county and distrct data, without producing gaps between boundaries.
I’ve been testing this with v.generalize in grass via QuantumGIS - I’ve had tons of issues with the Grass toolbox crashing, but have narrowed down to using the Hermite algorithm. While it works, I’m having some bizarre issues with it. Apologies for the cross-post with the PostGIS mailing list.

In the attached gif of California counties, from left to right, I have used the following tolerance values with the Hermite algorithm:

  • original
  • 1.0
  • 0.08
  • 0.01
  • 0.00001

Why do counties disappear entirely as I decrease the tolerance?

In the Grass Tools I choose the v.generalize function. I choose Boundary as the feature type (though I’ve tried checking others, as well as all of them and it doesn’t seem to change anything). Everything else is default, except for tolerance as notated above.

When I tested this originally on only Arkansas and Mississippi, I got really nice results. I then tried it on the entire US and had the missing counties problem. So I tried only California, and still have the same issue.

I’ve tried other algorithms, but this has so far given me the detail I want - of course sans counties! Any thoughts?

Thanks,

  • Chris
(attachments)

CA.gif

2

On Thu, Jun 30, 2011 at 4:01 PM, Christian Guirreri
<christian@guirreri.com> wrote:

I'm a brand new user to GIS - my goal right now is to heavily simplify Tiger
2010 county and distrct data, without producing gaps between boundaries.
I've been testing this with v.generalize in grass via QuantumGIS - I've had
tons of issues with the Grass toolbox crashing, but have narrowed down to
using the Hermite algorithm. While it works, I'm having some bizarre issues
with it. Apologies for the cross-post with the PostGIS mailing list.

In the attached gif of California counties, from left to right, I have used
the following tolerance values with the Hermite algorithm:
- original
- 1.0
- 0.08
- 0.01
- 0.00001

Why do counties disappear entirely as I decrease the tolerance?

This problem has been fixed in GRASS 6.4 only 2 weeks ago (June 13).
Please update your GRASS version if possible.

Markus M

In the Grass Tools I choose the v.generalize function. I choose Boundary as
the feature type (though I've tried checking others, as well as all of them
and it doesn't seem to change anything). Everything else is default, except
for tolerance as notated above.

When I tested this originally on only Arkansas and Mississippi, I got really
nice results. I then tried it on the entire US and had the missing counties
problem. So I tried only California, and still have the same issue.

I've tried other algorithms, but this has so far given me the detail I want
- of course sans counties! Any thoughts?

Thanks,
- Chris
_______________________________________________
grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

3

I’m on GRASS 6.4.1. QGIS 1.7.0

On Thu, Jun 30, 2011 at 10:18 AM, Markus Metz <markus.metz.giswork@googlemail.com> wrote:

On Thu, Jun 30, 2011 at 4:01 PM, Christian Guirreri
<christian@guirreri.com> wrote:

I’m a brand new user to GIS - my goal right now is to heavily simplify Tiger
2010 county and distrct data, without producing gaps between boundaries.
I’ve been testing this with v.generalize in grass via QuantumGIS - I’ve had
tons of issues with the Grass toolbox crashing, but have narrowed down to
using the Hermite algorithm. While it works, I’m having some bizarre issues
with it. Apologies for the cross-post with the PostGIS mailing list.

In the attached gif of California counties, from left to right, I have used
the following tolerance values with the Hermite algorithm:

  • original
  • 1.0
  • 0.08
  • 0.01
  • 0.00001

Why do counties disappear entirely as I decrease the tolerance?

This problem has been fixed in GRASS 6.4 only 2 weeks ago (June 13).
Please update your GRASS version if possible.

Markus M

In the Grass Tools I choose the v.generalize function. I choose Boundary as
the feature type (though I’ve tried checking others, as well as all of them
and it doesn’t seem to change anything). Everything else is default, except
for tolerance as notated above.

When I tested this originally on only Arkansas and Mississippi, I got really
nice results. I then tried it on the entire US and had the missing counties
problem. So I tried only California, and still have the same issue.

I’ve tried other algorithms, but this has so far given me the detail I want

  • of course sans counties! Any thoughts?

Thanks,

  • Chris

grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

4

I’ve experienced problems with calling up vectors stored in the GRASS database with QGIS, sometimes vectors simply are missing. Does the same problem occur in the GRASS environment? Maybe it would help to try showing the vectors in GRASS directly. If that work it means that QGIS is just having a problem where it calls up the vectors from GRASS. My problem was fixable by exporting the vectors as a shapefile and then loading them in QGIS.

–
B.Sc. Daniel Lee
Geschäftsführung für Forschung und Entwicklung
ISIS - International Solar Information Solutions

Deutschhausstr. 10
35037 Marburg
Festnetz: +49 6421 379 6256
Mobil: +49 176 6127 7269
E-Mail: Lee@isi-solutions.org
Web: http://www.isi-solutions.org

Am 30.06.2011 16:02 schrieb “Christian Guirreri” <christian@guirreri.com>:

I’m a brand new user to GIS - my goal right now is to heavily simplify Tiger
2010 county and distrct data, without producing gaps between boundaries.
I’ve been testing this with v.generalize in grass via QuantumGIS - I’ve had
tons of issues with the Grass toolbox crashing, but have narrowed down to
using the Hermite algorithm. While it works, I’m having some bizarre issues
with it. Apologies for the cross-post with the PostGIS mailing list.

In the attached gif of California counties, from left to right, I have used
the following tolerance values with the Hermite algorithm:

  • original
  • 1.0
  • 0.08
  • 0.01
  • 0.00001

Why do counties disappear entirely as I decrease the tolerance?

In the Grass Tools I choose the v.generalize function. I choose Boundary as
the feature type (though I’ve tried checking others, as well as all of them
and it doesn’t seem to change anything). Everything else is default, except
for tolerance as notated above.

When I tested this originally on only Arkansas and Mississippi, I got really
nice results. I then tried it on the entire US and had the missing counties
problem. So I tried only California, and still have the same issue.

I’ve tried other algorithms, but this has so far given me the detail I want

  • of course sans counties! Any thoughts?

Thanks,

  • Chris
5

Understood. I actually started to try using some of the GRASS interface via QGIS, but on some of the panels, such as v.generalize, I couldn’t type in a tolerance value. I’m on Win7 x64.

I’m going to try a fresh install of GRASS.

On Thu, Jun 30, 2011 at 10:52 AM, Daniel Lee <lee@isi-solutions.org> wrote:

I’ve experienced problems with calling up vectors stored in the GRASS database with QGIS, sometimes vectors simply are missing. Does the same problem occur in the GRASS environment? Maybe it would help to try showing the vectors in GRASS directly. If that work it means that QGIS is just having a problem where it calls up the vectors from GRASS. My problem was fixable by exporting the vectors as a shapefile and then loading them in QGIS.

–
B.Sc. Daniel Lee
Geschäftsführung für Forschung und Entwicklung
ISIS - International Solar Information Solutions

Deutschhausstr. 10
35037 Marburg
Festnetz: +49 6421 379 6256
Mobil: +49 176 6127 7269
E-Mail: Lee@isi-solutions.org
Web: http://www.isi-solutions.org

Am 30.06.2011 16:02 schrieb “Christian Guirreri” <christian@guirreri.com>:

I’m a brand new user to GIS - my goal right now is to heavily simplify Tiger
2010 county and distrct data, without producing gaps between boundaries.
I’ve been testing this with v.generalize in grass via QuantumGIS - I’ve had
tons of issues with the Grass toolbox crashing, but have narrowed down to
using the Hermite algorithm. While it works, I’m having some bizarre issues
with it. Apologies for the cross-post with the PostGIS mailing list.

In the attached gif of California counties, from left to right, I have used
the following tolerance values with the Hermite algorithm:

  • original
  • 1.0
  • 0.08
  • 0.01
  • 0.00001

Why do counties disappear entirely as I decrease the tolerance?

In the Grass Tools I choose the v.generalize function. I choose Boundary as
the feature type (though I’ve tried checking others, as well as all of them
and it doesn’t seem to change anything). Everything else is default, except
for tolerance as notated above.

When I tested this originally on only Arkansas and Mississippi, I got really
nice results. I then tried it on the entire US and had the missing counties
problem. So I tried only California, and still have the same issue.

I’ve tried other algorithms, but this has so far given me the detail I want

  • of course sans counties! Any thoughts?

Thanks,

  • Chris
6

On Thu, Jun 30, 2011 at 4:47 PM, Christian Guirreri
<christian@guirreri.com> wrote:

I'm on GRASS 6.4.1. QGIS 1.7.0

In this version, v.generalize is still broken. You would need a recent
version of GRASS 6.4.2. For Windows, you can get a recent version
here:

http://wingrass.fsv.cvut.cz/grass64/

Markus M

On Thu, Jun 30, 2011 at 10:18 AM, Markus Metz
<markus.metz.giswork@googlemail.com> wrote:

On Thu, Jun 30, 2011 at 4:01 PM, Christian Guirreri
<christian@guirreri.com> wrote:
> I'm a brand new user to GIS - my goal right now is to heavily simplify
> Tiger
> 2010 county and distrct data, without producing gaps between boundaries.
> I've been testing this with v.generalize in grass via QuantumGIS - I've
> had
> tons of issues with the Grass toolbox crashing, but have narrowed down
> to
> using the Hermite algorithm. While it works, I'm having some bizarre
> issues
> with it. Apologies for the cross-post with the PostGIS mailing list.
>
> In the attached gif of California counties, from left to right, I have
> used
> the following tolerance values with the Hermite algorithm:
> - original
> - 1.0
> - 0.08
> - 0.01
> - 0.00001
>
> Why do counties disappear entirely as I decrease the tolerance?
>
This problem has been fixed in GRASS 6.4 only 2 weeks ago (June 13).
Please update your GRASS version if possible.

Markus M

> In the Grass Tools I choose the v.generalize function. I choose Boundary
> as
> the feature type (though I've tried checking others, as well as all of
> them
> and it doesn't seem to change anything). Everything else is default,
> except
> for tolerance as notated above.
>
> When I tested this originally on only Arkansas and Mississippi, I got
> really
> nice results. I then tried it on the entire US and had the missing
> counties
> problem. So I tried only California, and still have the same issue.
>
> I've tried other algorithms, but this has so far given me the detail I
> want
> - of course sans counties! Any thoughts?
>
> Thanks,
> - Chris
> _______________________________________________
> grass-user mailing list
> grass-user@lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/grass-user
>
>

7

Success! Thanks for making this easy for the total noob that I am.

On Thu, Jun 30, 2011 at 11:04 AM, Markus Metz <markus.metz.giswork@googlemail.com> wrote:

On Thu, Jun 30, 2011 at 4:47 PM, Christian Guirreri
<christian@guirreri.com> wrote:

I’m on GRASS 6.4.1. QGIS 1.7.0

In this version, v.generalize is still broken. You would need a recent
version of GRASS 6.4.2. For Windows, you can get a recent version
here:

http://wingrass.fsv.cvut.cz/grass64/

Markus M

On Thu, Jun 30, 2011 at 10:18 AM, Markus Metz
<markus.metz.giswork@googlemail.com> wrote:

On Thu, Jun 30, 2011 at 4:01 PM, Christian Guirreri
<christian@guirreri.com> wrote:

I’m a brand new user to GIS - my goal right now is to heavily simplify
Tiger
2010 county and distrct data, without producing gaps between boundaries.
I’ve been testing this with v.generalize in grass via QuantumGIS - I’ve
had
tons of issues with the Grass toolbox crashing, but have narrowed down
to
using the Hermite algorithm. While it works, I’m having some bizarre
issues
with it. Apologies for the cross-post with the PostGIS mailing list.

In the attached gif of California counties, from left to right, I have
used
the following tolerance values with the Hermite algorithm:

  • original
  • 1.0
  • 0.08
  • 0.01
  • 0.00001

Why do counties disappear entirely as I decrease the tolerance?

This problem has been fixed in GRASS 6.4 only 2 weeks ago (June 13).
Please update your GRASS version if possible.

Markus M

In the Grass Tools I choose the v.generalize function. I choose Boundary
as
the feature type (though I’ve tried checking others, as well as all of
them
and it doesn’t seem to change anything). Everything else is default,
except
for tolerance as notated above.

When I tested this originally on only Arkansas and Mississippi, I got
really
nice results. I then tried it on the entire US and had the missing
counties
problem. So I tried only California, and still have the same issue.

I’ve tried other algorithms, but this has so far given me the detail I
want

  • of course sans counties! Any thoughts?

Thanks,

  • Chris

grass-user mailing list
grass-user@lists.osgeo.org
http://lists.osgeo.org/mailman/listinfo/grass-user

8

On Thu, Jun 30, 2011 at 7:49 PM, Christian Guirreri <guirreri@gmail.com> wrote:

I suppose my other question is if anyone has any recommendations concerning
v.generalize as it applies specifically to tiger data - I'm doing all of US.
Lots of settings and tests and its a bit overwhelming for a newbie.

For simplification (vertex reduction), Douglas-Peucker is generally a
good choice, it's relatively simple and commonly used.

For smoothing, Chaiken's Algorithm and Hermite Interpolation should
produce quite different results, apart from being a matter of taste,
it depends on what kind of modifications are allowed.

Markus M

On Jun 30, 2011 11:33 AM, "Christian Guirreri" <christian@guirreri.com>
wrote:

Success! Thanks for making this easy for the total noob that I am.

On Thu, Jun 30, 2011 at 11:04 AM, Markus Metz <
markus.metz.giswork@googlemail.com> wrote:

On Thu, Jun 30, 2011 at 4:47 PM, Christian Guirreri
<christian@guirreri.com> wrote:
> I'm on GRASS 6.4.1. QGIS 1.7.0
>
In this version, v.generalize is still broken. You would need a recent
version of GRASS 6.4.2. For Windows, you can get a recent version
here:

http://wingrass.fsv.cvut.cz/grass64/

Markus M

> On Thu, Jun 30, 2011 at 10:18 AM, Markus Metz
> <markus.metz.giswork@googlemail.com> wrote:
>>
>> On Thu, Jun 30, 2011 at 4:01 PM, Christian Guirreri
>> <christian@guirreri.com> wrote:
>> > I'm a brand new user to GIS - my goal right now is to heavily
>> > simplify
>> > Tiger
>> > 2010 county and distrct data, without producing gaps between
boundaries.
>> > I've been testing this with v.generalize in grass via QuantumGIS -
I've
>> > had
>> > tons of issues with the Grass toolbox crashing, but have narrowed
>> > down
>> > to
>> > using the Hermite algorithm. While it works, I'm having some bizarre
>> > issues
>> > with it. Apologies for the cross-post with the PostGIS mailing list.
>> >
>> > In the attached gif of California counties, from left to right, I
>> > have
>> > used
>> > the following tolerance values with the Hermite algorithm:
>> > - original
>> > - 1.0
>> > - 0.08
>> > - 0.01
>> > - 0.00001
>> >
>> > Why do counties disappear entirely as I decrease the tolerance?
>> >
>> This problem has been fixed in GRASS 6.4 only 2 weeks ago (June 13).
>> Please update your GRASS version if possible.
>>
>> Markus M
>>
>>
>> > In the Grass Tools I choose the v.generalize function. I choose
Boundary
>> > as
>> > the feature type (though I've tried checking others, as well as all
>> > of
>> > them
>> > and it doesn't seem to change anything). Everything else is default,
>> > except
>> > for tolerance as notated above.
>> >
>> > When I tested this originally on only Arkansas and Mississippi, I
>> > got
>> > really
>> > nice results. I then tried it on the entire US and had the missing
>> > counties
>> > problem. So I tried only California, and still have the same issue.
>> >
>> > I've tried other algorithms, but this has so far given me the detail
>> > I
>> > want
>> > - of course sans counties! Any thoughts?
>> >
>> > Thanks,
>> > - Chris
>> > _______________________________________________
>> > grass-user mailing list
>> > grass-user@lists.osgeo.org
>> > http://lists.osgeo.org/mailman/listinfo/grass-user
>> >
>> >
>
>