Re: [jts-devel] Intersections of cells in a GridCoverage with a LineString

Mon, 02 Mar 2009 09:12:18 -0800

How about creating a set of polygons equal in shape to your grid cells, and then intersect the line string with each polygon that it touches? You can use a spatial index (STRtree) to speed up finding candidate polygons. 
Martin

Pete Ballack wrote:

Hello,
I posted the same question on the geotools-user-list and Michael Bedward responded as follows "However, I suggest you pose the same question on the JTS list where 
Martin Davis and the other geometric gurus might be able to help."
So here is my message... 


I painted a small Graphic that should help to understand my current 
problem (I didn't want to post it on the mailing list directly)


Here is the Link to the graphic.
http://bayimg.com/oaNDJAaBn


I created a GridCoverage with a specified cellsize to rasterize an area

double width = envelope.getWidth(); // i.e. 1000m
double height = envelope.getHeight(); // i.e. 1000m

int numCellX = (int) Math.floor( width / cellSize ); // cellSize i.e. 10m
int numCellY = (int) Math.floor( height / cellSize );

WritableRaster raster = RasterFactory.createBandedRaster(
                DataBuffer.TYPE_FLOAT,
                numCellX, numCellY, 1, null );

GridCoverage2D gridCoverage = factory.create( "My coverage",
                raster,
                envelope );


Now my Problem:


The values of a cell in the raster depends on the length of the 
LineString covering the cell.
(in my Image the green part of the LineString would determine the 
value of d;2)


I belive that their is no function available doing that.

So my idea to solve my problem is some workaround I'm not really 
satisfied with.


1.create a graph corresponding to the raster (width, height and cellsize)

2.for a given LineString find all intersection points with the created 
graph

3.for all following intersection points (i, i+1)
       a.calculate the length -> value for the cell

       b.get the middle point between (i, i+1) to find the 
corresponding cell

       c.add value to cell

Maybe somebody has a smarter idea to solve my problem.

Thanks
Pete

 
here is the link to my posting on the geotools-mailing-list

http://n2.nabble.com/Intersections-of-cells-in-a-GridCoverage-with-a-LineString-td2405815.html

 
 
 
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jts-devel mailing list
[email protected]
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--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022


Hello,

 
I posted the same question on the geotools-user-list and Michael 
Bedward responded as follows
 
"However, I suggest you pose the same question on the JTS list where

Martin Davis and the other geometric gurus might be able to help."

 
So here is my message...



I painted a small Graphic that should help to understand my current 
problem (I didn't want to post it on the mailing list directly)


Here is the Link to the graphic.
http://bayimg.com/oaNDJAaBn


I created a GridCoverage with a specified cellsize to rasterize an area

double width = envelope.getWidth(); // i.e. 1000m
double height = envelope.getHeight(); // i.e. 1000m

int numCellX = (int) Math.floor( width / cellSize ); // cellSize i.e. 10m
int numCellY = (int) Math.floor( height / cellSize );

WritableRaster raster = RasterFactory.createBandedRaster(
                DataBuffer.TYPE_FLOAT,
                numCellX, numCellY, 1, null );

GridCoverage2D gridCoverage = factory.create( "My coverage",
                raster,
                envelope );


Now my Problem:


The values of a cell in the raster depends on the length of the 
LineString covering the cell.
(in my Image the green part of the LineString would determine the 
value of d;2)


I belive that their is no function available doing that.

So my idea to solve my problem is some workaround I'm not really 
satisfied with.


1.create a graph corresponding to the raster (width, height and cellsize)

2.for a given LineString find all intersection points with the created 
graph

3.for all following intersection points (i, i+1)
       a.calculate the length -> value for the cell

       b.get the middle point between (i, i+1) to find the 
corresponding cell

       c.add value to cell

Maybe somebody has a smarter idea to solve my problem.

Thanks
Pete

 
here is the link to my posting on the geotools-mailing-list

http://n2.nabble.com/Intersections-of-cells-in-a-GridCoverage-with-a-LineString-td2405815.html

 
 
 
------------------------------------------------------------------------


_______________________________________________
jts-devel mailing list
[email protected]
http://lists.refractions.net/mailman/listinfo/jts-devel

  


--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022


Hello,

 
I posted the same question on the geotools-user-list and Michael 
Bedward responded as follows
 
"However, I suggest you pose the same question on the JTS list where

Martin Davis and the other geometric gurus might be able to help."

 
So here is my message...



I painted a small Graphic that should help to understand my current 
problem (I didn't want to post it on the mailing list directly)


Here is the Link to the graphic.
http://bayimg.com/oaNDJAaBn


I created a GridCoverage with a specified cellsize to rasterize an area

double width = envelope.getWidth(); // i.e. 1000m
double height = envelope.getHeight(); // i.e. 1000m

int numCellX = (int) Math.floor( width / cellSize ); // cellSize i.e. 10m
int numCellY = (int) Math.floor( height / cellSize );

WritableRaster raster = RasterFactory.createBandedRaster(
                DataBuffer.TYPE_FLOAT,
                numCellX, numCellY, 1, null );

GridCoverage2D gridCoverage = factory.create( "My coverage",
                raster,
                envelope );


Now my Problem:


The values of a cell in the raster depends on the length of the 
LineString covering the cell.
(in my Image the green part of the LineString would determine the 
value of d;2)


I belive that their is no function available doing that.

So my idea to solve my problem is some workaround I'm not really 
satisfied with.


1.create a graph corresponding to the raster (width, height and cellsize)

2.for a given LineString find all intersection points with the created 
graph

3.for all following intersection points (i, i+1)
       a.calculate the length -> value for the cell

       b.get the middle point between (i, i+1) to find the 
corresponding cell

       c.add value to cell

Maybe somebody has a smarter idea to solve my problem.

Thanks
Pete

 
here is the link to my posting on the geotools-mailing-list

http://n2.nabble.com/Intersections-of-cells-in-a-GridCoverage-with-a-LineString-td2405815.html

 
 
 
------------------------------------------------------------------------


_______________________________________________
jts-devel mailing list
[email protected]
http://lists.refractions.net/mailman/listinfo/jts-devel

  


--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022


Hello,

 
I posted the same question on the geotools-user-list and Michael 
Bedward responded as follows
 
"However, I suggest you pose the same question on the JTS list where

Martin Davis and the other geometric gurus might be able to help."

 
So here is my message...



I painted a small Graphic that should help to understand my current 
problem (I didn't want to post it on the mailing list directly)


Here is the Link to the graphic.
http://bayimg.com/oaNDJAaBn


I created a GridCoverage with a specified cellsize to rasterize an area

double width = envelope.getWidth(); // i.e. 1000m
double height = envelope.getHeight(); // i.e. 1000m

int numCellX = (int) Math.floor( width / cellSize ); // cellSize i.e. 10m
int numCellY = (int) Math.floor( height / cellSize );

WritableRaster raster = RasterFactory.createBandedRaster(
                DataBuffer.TYPE_FLOAT,
                numCellX, numCellY, 1, null );

GridCoverage2D gridCoverage = factory.create( "My coverage",
                raster,
                envelope );


Now my Problem:


The values of a cell in the raster depends on the length of the 
LineString covering the cell.
(in my Image the green part of the LineString would determine the 
value of d;2)


I belive that their is no function available doing that.

So my idea to solve my problem is some workaround I'm not really 
satisfied with.


1.create a graph corresponding to the raster (width, height and cellsize)

2.for a given LineString find all intersection points with the created 
graph

3.for all following intersection points (i, i+1)
       a.calculate the length -> value for the cell

       b.get the middle point between (i, i+1) to find the 
corresponding cell

       c.add value to cell

Maybe somebody has a smarter idea to solve my problem.

Thanks
Pete

 
here is the link to my posting on the geotools-mailing-list

http://n2.nabble.com/Intersections-of-cells-in-a-GridCoverage-with-a-LineString-td2405815.html

 
 
 
------------------------------------------------------------------------


_______________________________________________
jts-devel mailing list
[email protected]
http://lists.refractions.net/mailman/listinfo/jts-devel

  


--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022

_______________________________________________
jts-devel mailing list
[email protected]
http://lists.refractions.net/mailman/listinfo/jts-devel






















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