------------------------------
Message: 7
Date: Thu, 29 May 2008 13:16:04 +1000
From: "andrew haywood" <ahaywood3@gmail.com>
Subject: [GRASS-user] newbie: processing lidar with r.in.xyz
To: grass-user@lists.osgeo.org
Message-ID:
<7a4569180805282016s3212c78ck2c35344b95650a7a@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
Dear List,
i am currently enjoying the flexibility of using r.in.xyz to process lidar
data over native forests in Victoria, Australia.Thank you hamish for such a
great tool.
At this stage I have 'binned' my data into 20m cells and calculated a number
of metrics (including 13 vegetation height percentiles p5 p10 p20 .. p90,
p95, p99) based on the z values.
What I was wondering is how can I calculate the mean intensity for the
associated height percentiles.
To get around this I have written a script in a proprietary stats package to
create the intensity metrics. However, I would prefer to use Grass and
opensource tools to do this binning
Any suggestions would be appreciated!!!!
My data is in the following format
x|y|ground|intensity|class|canopy_top|height
410774.45|5820999.93|773.3|23|10|766.0983886719|7.20161
410763.07|5820999.9|802.27|2|10|763.9434814453|38.3265
410765.47|5820999.94|773.11|90|10|764.2877807617|8.82222
410758.09|5820999.95|807.99|47|10|762.8372192383|45.1528
410748.12|5820999.93|760.89|8|10|760.5731811523|0.316819
Andrew,
At the risk of sounding thick, I'd like to know what "intensity" represents in your context ... Regarding statistical packages, since R is grass-linked, why not do the calcs in R?
Richard Chirgwin
...
I suspect I should start to learn python.
regards
Andy
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Message: 8
Date: Thu, 29 May 2008 11:17:48 +0800
From: "maning sambale" <emmanuel.sambale@gmail.com>
Subject: Re: [GRASS-user] Triangles polygons with Arc*
To: grass-user <grass-user@lists.osgeo.org>
Message-ID:
<f902f9840805282017y2bae1830y786aa244a5dc60f6@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Just curious if anybody encountered this issue with Arc*:
it's a common problem.
It does seem to be.
short answer: TINs stink. Raster maps created from TINs stink more.
My colleague used SRTM DEM converted to grid format of Arc
He mentioned that it is fairly common when you convert raster grids in
arc to vectors (shapefiles). Especially with very small areas like a
2-3 pixels. Will look into this further.
To all the others who gave me a list of Arc mailing list thanks! I am
reading a few right now.
cheers,
maning
Hi Richard,
the lidar system emits a pulse of focused light in the near infrared region of the electromagnetic spectrum and detects the radiation reflected back from the target. Lidar intensity, is the intensity of each return pulse (ive seen it referred to as laser amplitude), it represents the reflected energy and provides a concentrated measurements of the object’s reflectance unaffected by shadows or occlusions. This reflectance may vary based on the reflectance properties of the targeted material.
Most often in Australia the data suppliers provide a flatfile containing x,y,x,i . where i is the intensity of the pulse. Each pulse is then classified as ground or non ground (or vegetation in my case). Ive simply taken the non-ground hits and removed the ground elevation (DTM) to get a relative canopy height of my vegetation.
RE Stats package. I would like to use R but I have 1200 2kmby2km tiles with approximately 3 billion points (approximately 700 Gb). r.in.xyz and its statistics is an amazingly quick way to calculate summary statistics in a grid format. Using a stats package just seems to have too much overhead. Ive started to write a python program to read the flat files and calculate summary statistics for the grid cells.
My problem is I can calculate 13 canopy height percentiles for my 20m resolution grid cells really quickly with r.in.xyz- but then I wanted for the same height percentiles the mean intensity values (basically a two classification table on height percentiles and intensity) and was wondering if it was possible to do this in grass easily.
cheers
Andy
On Thu, May 29, 2008 at 7:18 PM, Richard Chirgwin <rchirgwin@ozemail.com.au> wrote:
Message: 7
Date: Thu, 29 May 2008 13:16:04 +1000
From: “andrew haywood” <ahaywood3@gmail.com>
Subject: [GRASS-user] newbie: processing lidar with r.in.xyz
To: grass-user@lists.osgeo.org
Message-ID:
<7a4569180805282016s3212c78ck2c35344b95650a7a@mail.gmail.com>
Content-Type: text/plain; charset=“iso-8859-1”
Dear List,
i am currently enjoying the flexibility of using r.in.xyz to process lidar
data over native forests in Victoria, Australia.Thank you hamish for such a
great tool.
At this stage I have ‘binned’ my data into 20m cells and calculated a number
of metrics (including 13 vegetation height percentiles p5 p10 p20 … p90,
p95, p99) based on the z values.
What I was wondering is how can I calculate the mean intensity for the
associated height percentiles.
To get around this I have written a script in a proprietary stats package to
create the intensity metrics. However, I would prefer to use Grass and
opensource tools to do this binning
Any suggestions would be appreciated!!!
My data is in the following format
x|y|ground|intensity|class|canopy_top|height
410774.45|5820999.93|773.3|23|10|766.0983886719|7.20161
410763.07|5820999.9|802.27|2|10|763.9434814453|38.3265
410765.47|5820999.94|773.11|90|10|764.2877807617|8.82222
410758.09|5820999.95|807.99|47|10|762.8372192383|45.1528
410748.12|5820999.93|760.89|8|10|760.5731811523|0.316819
Andrew,
At the risk of sounding thick, I’d like to know what “intensity” represents in your context … Regarding statistical packages, since R is grass-linked, why not do the calcs in R?
Richard Chirgwin
…
…
…
I suspect I should start to learn python.
regards
Andy
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Message: 8
Date: Thu, 29 May 2008 11:17:48 +0800
From: “maning sambale” <emmanuel.sambale@gmail.com>
Subject: Re: [GRASS-user] Triangles polygons with Arc*
To: grass-user <grass-user@lists.osgeo.org>
Message-ID:
<f902f9840805282017y2bae1830y786aa244a5dc60f6@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Just curious if anybody encountered this issue with Arc*:
it’s a common problem.
It does seem to be.
short answer: TINs stink. Raster maps created from TINs stink more.
My colleague used SRTM DEM converted to grid format of Arc
He mentioned that it is fairly common when you convert raster grids in
arc to vectors (shapefiles). Especially with very small areas like a
2-3 pixels. Will look into this further.
To all the others who gave me a list of Arc mailing list thanks! I am
reading a few right now.
cheers,
maning
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