Re: [Qgis-user] combining fragmented forests

[Frank Broniewski]

Hi Reiko,

another idea might be to use a buffer to stitch polygons together. Use a 
small buffer value and choose to dissolve the resulting polygons. That 
method does not however preserve meaningful attribute values.


Let's know how your progress goes,
Frank

Am 06.05.20 um 20:55 schrieb RMG:

Hello,

I have five shapefiles that contain thousands of fragmented forests that 
I created from a NDVI raster of a large protected area in West Africa, 
which I separated into five panels. Now, how do I stitch thousands of 
the fragmented forests at the borders?


Each shapefile's attributes have ID, count (number of units), area, and 
perimeter, so I can visually recognize which fragments need stitching, 
but because there are so many, I don't think I can do it manually.


Any help would be appreciated.

Best wishes,


Reiko Matsuda Goodwin
Comoé Monkey Project 
Guenon Conservation Community 





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Re: [Qgis-user] combining fragmented forests (RMG)

[Falk Huettmann]

Hi there,

greetings;
I have seen and done such things, a lot,
and I would like to give you a message of caution about it.

One serious problem is here that it includes error inconsistencies (sheet
edges vs sheet centers),
another one is about classes and patches that are incorrect to start with
(all sheets; merged or not).

In other words,
there are several types of errors in such 'technical artefacts' aka  merged
forest patch maps;
they "cannot be used for navigation", to put it politely.
It's a blurr of things, and a major problem with forest maps and forest
inventory maps out there.

I know of forest maps and regions that have accuracies of 40%, if
ground-truthed.
So yes, they look great on the screen and in GIS but are close to random
(50% accuracy)
if ever used and interpreted for applications.
Please be aware; happy to hear about a fix; beyond technical GIS ones, or
rubber sheeting.

Keep me posted please; thanks.
Very best
   Falk

PS There is currently no single accepted map of global forest cover;
FAO, IUFRO etc cannot really agree on such details whatsoever.
And yes, Remote Sensing products, LIDAR and air photo interpretation
can be rather poor for quality, usually they are.











On Wed, May 6, 2020 at 2:50 PM Michael Harte  wrote:

> Reiko,
>
> You could try something like this:
>
>
>1. Merge all forests into a single file (if you haven't already);
>2. Create a new field in the forests table called something like
>"border"
>3. Create lines that trace the panel boundaries, that separate the
>forests you want to join;
>4. Buffer each of those lines by some small distance  (try 1 meter);
>5. For each buffer "Select by location" all features in forests that
>intersect buffer;
>6. Use the field calculator in the table to enter a unique identifier
>for the selected features in the "border" field;
>7. Do this for each buffer;
>8. Dissolve the forest layer on the border field.
>
> Feel free to get in touch.
>
> Cheers,
>
> Mike
>
>
>
> Message: 1
> Date: Wed, 6 May 2020 14:55:30 -0400
> From: RMG  
> To: qgis-user@lists.osgeo.org
> Subject: [Qgis-user] combining fragmented forests
> Message-ID:
>
> 
> Content-Type: text/plain; charset="utf-8"
>
> Hello,
>
> I have five shapefiles that contain thousands of fragmented forests that I
> created from a NDVI raster of a large protected area in West Africa, which
> I separated into five panels. Now, how do I stitch thousands of the
> fragmented forests at the borders?
>
> Each shapefile's attributes have ID, count (number of units), area, and
> perimeter, so I can visually recognize which fragments need stitching, but
> because there are so many, I don't think I can do it manually.
>
> Any help would be appreciated.
>
> Best wishes,
>
>
> Reiko Matsuda Goodwin
> Comoé Monkey Project <https://www.facebook.com/ComoeMonkeyProject/> 
> <https://www.facebook.com/ComoeMonkeyProject/>
> Guenon Conservation 
> Community<http://facebook.com/GuenonConservationCommunity/> 
> <http://facebook.com/GuenonConservationCommunity/>
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Re: [Qgis-user] combining fragmented forests (RMG)

[Michael Harte]

Reiko,

You could try something like this:

1. Merge all forests into a single file (if you haven't already);
2. Create a new field in the forests table called something like "border"
3. Create lines that trace the panel boundaries, that separate the
   forests you want to join;
4. Buffer each of those lines by some small distance  (try 1 meter);
5. For each buffer "Select by location" all features in forests that
   intersect buffer;
6. Use the field calculator in the table to enter a unique identifier
   for the selected features in the "border" field;
7. Do this for each buffer;
8. Dissolve the forest layer on the border field.

Feel free to get in touch.

Cheers,

Mike




Message: 1
Date: Wed, 6 May 2020 14:55:30 -0400
From: RMG
To:qgis-user@lists.osgeo.org
Subject: [Qgis-user] combining fragmented forests
Message-ID:

Content-Type: text/plain; charset="utf-8"

Hello,

I have five shapefiles that contain thousands of fragmented forests that I
created from a NDVI raster of a large protected area in West Africa, which
I separated into five panels. Now, how do I stitch thousands of the
fragmented forests at the borders?

Each shapefile's attributes have ID, count (number of units), area, and
perimeter, so I can visually recognize which fragments need stitching, but
because there are so many, I don't think I can do it manually.

Any help would be appreciated.

Best wishes,


Reiko Matsuda Goodwin
Comoé Monkey Project<https://www.facebook.com/ComoeMonkeyProject/>
Guenon Conservation Community
<http://facebook.com/GuenonConservationCommunity/>
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Re: [Qgis-user] combining fragmented forests

[Nicolas Cadieux]

Hi,

You can merge the borders while using a Field in the shapefiles.  Look in the 
processing toolbox for merge.

Nicolas Cadieux
Ça va bien aller!

> Le 6 mai 2020 à 16:10, RMG  a écrit :
> 
>  Hello Chris,
> 
> I need to stitch those broken up forests at the shared borders across the 
> tiles. 
> 
> Best wishes,
> 
> Reiko Matsuda Goodwin, PhD (she, her)
> 
> Sent from my iPhone 
> 
>> On May 6, 2020, at 15:57, chris hermansen  wrote:
>> 
>> Reiko and list
>> 
>>> On Wed, May 6, 2020 at 11:55 AM RMG  wrote:
>>> Hello,
>>> 
>>> I have five shapefiles that contain thousands of fragmented forests that I 
>>> created from a NDVI raster of a large protected area in West Africa, which 
>>> I separated into five panels. Now, how do I stitch thousands of the 
>>> fragmented forests at the borders?
>>> 
>>> Each shapefile's attributes have ID, count (number of units), area, and 
>>> perimeter, so I can visually recognize which fragments need stitching, but 
>>> because there are so many, I don't think I can do it manually.
>> 
>> Do you decide to "edge match" your polygons based on common attributes, or 
>> on some kind of geometric concern - shared border across tiles, for example? 
>> 
>> -- 
>> Chris Hermansen · clhermansen "at" gmail "dot" com
>> 
>> C'est ma façon de parler.
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Re: [Qgis-user] combining fragmented forests

[RMG]

Hello Chris,

I need to stitch those broken up forests at the shared borders across the 
tiles. 

Best wishes,

Reiko Matsuda Goodwin, PhD (she, her)

Sent from my iPhone 

> On May 6, 2020, at 15:57, chris hermansen  wrote:
> 
> Reiko and list
> 
>> On Wed, May 6, 2020 at 11:55 AM RMG  wrote:
>> Hello,
>> 
>> I have five shapefiles that contain thousands of fragmented forests that I 
>> created from a NDVI raster of a large protected area in West Africa, which I 
>> separated into five panels. Now, how do I stitch thousands of the fragmented 
>> forests at the borders?
>> 
>> Each shapefile's attributes have ID, count (number of units), area, and 
>> perimeter, so I can visually recognize which fragments need stitching, but 
>> because there are so many, I don't think I can do it manually.
> 
> Do you decide to "edge match" your polygons based on common attributes, or on 
> some kind of geometric concern - shared border across tiles, for example? 
> 
> -- 
> Chris Hermansen · clhermansen "at" gmail "dot" com
> 
> C'est ma façon de parler.
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Re: [Qgis-user] combining fragmented forests

[chris hermansen]

Reiko and list

On Wed, May 6, 2020 at 11:55 AM RMG  wrote:

> Hello,
>
> I have five shapefiles that contain thousands of fragmented forests that I
> created from a NDVI raster of a large protected area in West Africa, which
> I separated into five panels. Now, how do I stitch thousands of the
> fragmented forests at the borders?
>
> Each shapefile's attributes have ID, count (number of units), area, and
> perimeter, so I can visually recognize which fragments need stitching, but
> because there are so many, I don't think I can do it manually.
>

Do you decide to "edge match" your polygons based on common attributes, or
on some kind of geometric concern - shared border across tiles, for
example?

-- 
Chris Hermansen · clhermansen "at" gmail "dot" com

C'est ma façon de parler.
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[Qgis-user] combining fragmented forests

[RMG]

Hello,

I have five shapefiles that contain thousands of fragmented forests that I
created from a NDVI raster of a large protected area in West Africa, which
I separated into five panels. Now, how do I stitch thousands of the
fragmented forests at the borders?

Each shapefile's attributes have ID, count (number of units), area, and
perimeter, so I can visually recognize which fragments need stitching, but
because there are so many, I don't think I can do it manually.

Any help would be appreciated.

Best wishes,


Reiko Matsuda Goodwin
Comoé Monkey Project 
Guenon Conservation Community

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