[GRASS-user] Creation of a DEM

megha_shyam · March 24, 2007, 2:04pm

Please help me in creation of DEM.i have a vector layer contaning contour information.How to create a DEM model of this.Can you tell me the stpes to be followed

shyam

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quinonero_juan_manue · March 24, 2007, 4:45pm

1.- You have to transform the vector information to a rast layer, you can do it using the comand v.to.rast, baut before you have to determine the cell resolution using for example g.region res=meters

2.- If you wsnt to create a good DEM you have to change the units of the rast layer created, Only have to convert this layer from meter to centimeter using r,mapcalc ‘cm_layer=rast_meter*100.00’. That’s for obtain a good relation betwen horizontal and vertical resolution.

3.- Now you have to use an interpolatión method to create a DEM continous surface. There are several methods, the commonest is r.surf.contour tat use a lineal interpolation. If you use this command you must use the option -f and it’ll build faster, dont forget this point!!!

4.- Finally you have to transform the results to the correct units usin r.mapcalc ‘final_DEM=cm_DEM/100.00’

If you want to generate a DEM usin another interpolation methods please ask!!

Sorry for my english

Juanma

megha shyam capt_lms@yahoo.co.in escribió:

Please help me in creation of DEM.i have a vector layer contaning contour information.How to create a DEM model of this.Can you tell me the stpes to be followed

shyam

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Amaginary_Studios · March 24, 2007, 5:11pm

Actually I just finished learning how to do all this, thanks to the all the great help here.

You can review in the recent March Archive;

This is what I found to work for me.

I restricted my region setting to the bounds of my contours. * reason for this, I was told large areas of blank space can really slow down the processing time.
I forced the region settings to align to resolution also using “-a” ( or checking the “align to resolution…” check box under the “Bounds” tab for the “g.region” settings in gis.m
Display region settings to make sure everything looks good. * make sure resolution is a whole number not some odd ball 5.0009345321 I was told this may cause problems.

Now you can go either of Two ways (as far as I know). Both ways worked fine for me.

v.surf.rst

I essentially just inputted my vector map with contour data and specified the attribute column with the elevation info, named my raster output map… ** make sure your attribute column names are all in small caps in your vector table.

v.to.rast + r.surf.contour

both methods worked fine for me.

cheers.

Mars

On 24-Mar-07, at 7:04 AM, megha shyam wrote:

Please help me in creation of DEM.i have a vector layer contaning contour information.How to create a DEM model of this.Can you tell me the stpes to be followed

shyam

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ivan_marchesini1 · March 24, 2007, 5:20pm

Hi Megha,

import your vector map (e.g. with v.in.ogr)

then

g.region vect=yourvectormap #where yourvectormap is the map just
imported

g.region res=X #where X is the resolution of the dem you wish

v.surf.rst input=yourvectormap layer=1 zcolumn=column elev=elevation
#where column is the name of the table column containing elevation data
and elevation is the name of the DEM you need

try to have a look to

g.manual v.surf.rst

for more info on the interpolation procedure...

hope this help

Ivan

Il giorno sab, 24/03/2007 alle 14.04 +0000, megha shyam ha scritto:

Please help me in creation of DEM.i have a vector layer contaning
contour information.How to create a DEM model of this.Can you tell me
the stpes to be followed

shyam

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Edward_Tomlinson1 · June 30, 2007, 2:48am

Hi,

I am also trying to create a DEM from a shapefile.

Once again i have some questions about the cell resolution and the interpolation.

The use of this is for precision agriculture.

The shapefile was generated from a 2cm accuracy RTK GPS. Height variation is about 1 metre (over 1200metres). The shapefile isn’t exactly what you would call a contour map. The resulting shapefile is made up of rectangles of equal height. Each rectangle is 8m wide (always as this is the swath width used). The length varies as it keeps ~equal heights together. Technically i suppose this is a contour map, however equal height rectangles are not connected and are not part of the same shape…

My other problem is trying to work out what gradient splits should be used. As in i beleive i should use the standard deviation of height as the gradient step value. Does this sound correct??

Also i need to restrict the boudary of the DEM to another shapefile. It is just a single shape of the boundary of the field. Mostly all the data is there, however some interpolation will be needed.

Currently i am having trouble reading the file in using v.in.ogr.
command:
v.in.ogr ‘dsn=shapefile name’ output=elevation09 ‘layer=Elevation Map 9’
Result:
GRASS_INFO_WARNING Area size 9e…, area not imported
…
0 areas imported

THere are many columns in the .df file. How can i only import the ones i want? Clearly i have missed something.

Any help would be greatly appreciated.

THanks,
Ed

---------- Forwarded message ----------
From: quinonero juan manuel <jumaqu@yahoo.es>
Date: 25-Mar-2007 02:45
Subject: [GRASS-user] Creation of a DEM
To: grassuser@grass.itc.it

1.- You have to transform the vector information to a rast layer, you can do it using the comand v.to.rast, baut before you have to determine the cell resolution using for example g.region res=meters

2.- If you wsnt to create a good DEM you have to change the units of the rast layer created, Only have to convert this layer from meter to centimeter using r,mapcalc ‘cm_layer=rast_meter*100.00’. That’s for obtain a good relation betwen horizontal and vertical resolution.

3.- Now you have to use an interpolatión method to create a DEM continous surface. There are several methods, the commonest is r.surf.contour tat use a lineal interpolation. If you use this command you must use the option -f and it’ll build faster, dont forget this point!!!

4.- Finally you have to transform the results to the correct units usin r.mapcalc ‘final_DEM=cm_DEM/100.00’

If you want to generate a DEM usin another interpolation methods please ask!!

Sorry for my english

Juanma

megha shyam <capt_lms@yahoo.co.in> escribió:

Please help me in creation of DEM.i have a vector layer contaning contour information.How to create a DEM model of this.Can you tell me the stpes to be followed

shyam

Here’s a new way to find what you’re looking for - Yahoo! Answers _______________________________________________
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Dave_Kent · June 30, 2007, 5:35pm

Hi Ed:

I have had better luck creating DEMs using point data rather than area data. Can you get your RTK to export point data (xyz) rather than the swath segment data. Alternatively, use the “type=point” feature of v.in.ogr. I have never used this feature but the manual says it imports area centroids as points.

The next step is to interpret the point data to a DEM raster surface. I have used v.surf.rst to create a raster DEM from irregularly spaced points. It works well. You can use the “maskmap=name” feature to limit the DEM to a restricted area. v.surf.rst expects a raster map for maskmap. You can create one from your field outline shape file with v.to.rst .

I can’t help on the import problem. Perhaps importing the centroids only with “type=point” will help.

I think that precision agriculture is a natural application for Grass. It would be helpful and interesting to hear of your challenges and successes in its use.

Regards

Dave

On Jun 29, 2007, at 8:48 PM, Edward Tomlinson wrote:

Hi,

I am also trying to create a DEM from a shapefile.

Once again i have some questions about the cell resolution and the interpolation.

The use of this is for precision agriculture.

The shapefile was generated from a 2cm accuracy RTK GPS. Height variation is about 1 metre (over 1200metres). The shapefile isn’t exactly what you would call a contour map. The resulting shapefile is made up of rectangles of equal height. Each rectangle is 8m wide (always as this is the swath width used). The length varies as it keeps ~equal heights together. Technically i suppose this is a contour map, however equal height rectangles are not connected and are not part of the same shape…

My other problem is trying to work out what gradient splits should be used. As in i beleive i should use the standard deviation of height as the gradient step value. Does this sound correct??

Also i need to restrict the boudary of the DEM to another shapefile. It is just a single shape of the boundary of the field. Mostly all the data is there, however some interpolation will be needed.

Currently i am having trouble reading the file in using v.in.ogr.
command:
v.in.ogr ‘dsn=shapefile name’ output=elevation09 ‘layer=Elevation Map 9’
Result:
GRASS_INFO_WARNING Area size 9e…, area not imported
…
0 areas imported

THere are many columns in the .df file. How can i only import the ones i want? Clearly i have missed something.

Any help would be greatly appreciated.

THanks,
Ed

---------- Forwarded message ----------
From: quinonero juan manuel <jumaqu@yahoo.es>
Date: 25-Mar-2007 02:45
Subject: [GRASS-user] Creation of a DEM
To: grassuser@grass.itc.it

1.- You have to transform the vector information to a rast layer, you can do it using the comand v.to.rast, baut before you have to determine the cell resolution using for example g.region res=meters

2.- If you wsnt to create a good DEM you have to change the units of the rast layer created, Only have to convert this layer from meter to centimeter using r,mapcalc ‘cm_layer=rast_meter*100.00’. That’s for obtain a good relation betwen horizontal and vertical resolution.

3.- Now you have to use an interpolatión method to create a DEM continous surface. There are several methods, the commonest is r.surf.contour tat use a lineal interpolation. If you use this command you must use the option -f and it’ll build faster, dont forget this point!!!

4.- Finally you have to transform the results to the correct units usin r.mapcalc ‘final_DEM=cm_DEM/100.00’

If you want to generate a DEM usin another interpolation methods please ask!!

Sorry for my english

Juanma

megha shyam <capt_lms@yahoo.co.in> escribió:

Please help me in creation of DEM.i have a vector layer contaning contour information.How to create a DEM model of this.Can you tell me the stpes to be followed

shyam

Here’s a new way to find what you’re looking for - Yahoo! Answers _______________________________________________
grassuser mailing list
grassuser@grass.itc.it
http://grass.itc.it/mailman/listinfo/grassuser

LLama Gratis a cualquier PC del Mundo.
Llamadas a fijos y móviles desde 1 céntimo por minuto.
http://es.voice.yahoo.com

grassuser mailing list
grassuser@grass.itc.it
http://grass.itc.it/mailman/listinfo/grassuser

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cmbarton · June 30, 2007, 7:10pm

Ed,

It sounds like your shape file is made up of polygons, but that it needs to be cleaned.

The OGR layer warning is for one or more polygons that are extremely tiny. An area of 6.5e-11 means 6.5 with an exponent of -11. It is probably just ignoring these incorrect “polygons” (I bet that they are actually points instead of real polygons).

Ideally, you need to create your DEM from a point file. Probably a point at the center of each polygon is the best representation of your data. You can get these from area centroids after you import the polygons (use v.type to convert from centroids to points; in the vector>develop map>convert object types menu). Someone mentioned a v.in.OGR option to just import area centroids. I haven’t used this, but it might save a step.

The number of columns are irrelevant to interpolation, but they might slow down your import. They are stored in a *.dbf file along with your *.shp file. You can get rid of columns before your import with any program that will read DBF files (e.g., open office).

Once you have a point file with elevation values imported into GRASS, there are many interpolation methods available to you. The easiest way to see what is possible is to look at the raster>interpolate surfaces menu. You can interpolate from the vector points you have imported, or you can change the vector points to raster points (files>map type conversions) and use the raster points.

Michael

On 6/29/07 7:48 PM, “Edward Tomlinson” edwardjtomlinson@gmail.com wrote:

Hi,

I am also trying to create a DEM from a shapefile.

Once again i have some questions about the cell resolution and the interpolation.

The use of this is for precision agriculture.

The shapefile was generated from a 2cm accuracy RTK GPS. Height variation is about 1 metre (over 1200metres). The shapefile isn’t exactly what you would call a contour map. The resulting shapefile is made up of rectangles of equal height. Each rectangle is 8m wide (always as this is the swath width used). The length varies as it keeps ~equal heights together. Technically i suppose this is a contour map, however equal height rectangles are not connected and are not part of the same shape…

My other problem is trying to work out what gradient splits should be used. As in i beleive i should use the standard deviation of height as the gradient step value. Does this sound correct??

Also i need to restrict the boudary of the DEM to another shapefile. It is just a single shape of the boundary of the field. Mostly all the data is there, however some interpolation will be needed.

Currently i am having trouble reading the file in using v.in.ogr.
command:
v.in.ogr ‘dsn=shapefile name’ output=elevation09 ‘layer=Elevation Map 9’
Result:
GRASS_INFO_WARNING Area size 9e…, area not imported
…
0 areas imported

THere are many columns in the .df file. How can i only import the ones i want? Clearly i have missed something.

Any help would be greatly appreciated.

THanks,
Ed

---------- Forwarded message ----------
From: quinonero juan manuel jumaqu@yahoo.es
Date: 25-Mar-2007 02:45
Subject: [GRASS-user] Creation of a DEM
To: grassuser@grass.itc.it

1.- You have to transform the vector information to a rast layer, you can do it using the comand v.to.rast, baut before you have to determine the cell resolution using for example g.region res=meters

2.- If you wsnt to create a good DEM you have to change the units of the rast layer created, Only have to convert this layer from meter to centimeter using r,mapcalc ‘cm_layer=rast_meter*100.00’. That’s for obtain a good relation betwen horizontal and vertical resolution.

3.- Now you have to use an interpolatión method to create a DEM continous surface. There are several methods, the commonest is r.surf.contour tat use a lineal interpolation. If you use this command you must use the option -f and it’ll build faster, dont forget this point!!!

4.- Finally you have to transform the results to the correct units usin r.mapcalc ‘final_DEM=cm_DEM/100.00’

If you want to generate a DEM usin another interpolation methods please ask!!

Sorry for my english

Juanma

megha shyam capt_lms@yahoo.co.in escribió:

Please help me in creation of DEM.i have a vector layer contaning contour information.How to create a DEM model of this.Can you tell me the stpes to be followed

shyam

Here’s a new way to find what you’re looking for - Yahoo! Answers http://us.rd.yahoo.com/mail/in/yanswers/*http://in.answers.yahoo.com/ _______________________________________________
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Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton

Edward_Tomlinson1 · July 2, 2007, 2:05am

Thanks Michael and Dave,

It appears than my minimum area size was too big. I thought it said minimum area in square meters (using v.in.ogr) however on second reading it was square units. So after adjusting this it imported. However that is as far as i got. I am away for a week then i will atempt the rest of it (interpolation, DEM, etc).

Thanks again.
Ed

On 01/07/07, Michael Barton <michael.barton@asu.edu > wrote:

Ed,

It sounds like your shape file is made up of polygons, but that it needs to be cleaned.

The OGR layer warning is for one or more polygons that are extremely tiny. An area of 6.5e-11 means 6.5 with an exponent of -11. It is probably just ignoring these incorrect “polygons” (I bet that they are actually points instead of real polygons).

Ideally, you need to create your DEM from a point file. Probably a point at the center of each polygon is the best representation of your data. You can get these from area centroids after you import the polygons (use v.type to convert from centroids to points; in the vector>develop map>convert object types menu). Someone mentioned a v.in.OGR option to just import area centroids. I haven’t used this, but it might save a step.

The number of columns are irrelevant to interpolation, but they might slow down your import. They are stored in a *.dbf file along with your *.shp file. You can get rid of columns before your import with any program that will read DBF files ( e.g., open office).

Once you have a point file with elevation values imported into GRASS, there are many interpolation methods available to you. The easiest way to see what is possible is to look at the raster>interpolate surfaces menu. You can interpolate from the vector points you have imported, or you can change the vector points to raster points (files>map type conversions) and use the raster points.

Michael

On 6/29/07 7:48 PM, “Edward Tomlinson” < edwardjtomlinson@gmail.com > wrote:

Hi,

I am also trying to create a DEM from a shapefile.

Once again i have some questions about the cell resolution and the interpolation.

The use of this is for precision agriculture.

The shapefile was generated from a 2cm accuracy RTK GPS. Height variation is about 1 metre (over 1200metres). The shapefile isn’t exactly what you would call a contour map. The resulting shapefile is made up of rectangles of equal height. Each rectangle is 8m wide (always as this is the swath width used). The length varies as it keeps ~equal heights together. Technically i suppose this is a contour map, however equal height rectangles are not connected and are not part of the same shape…

My other problem is trying to work out what gradient splits should be used. As in i beleive i should use the standard deviation of height as the gradient step value. Does this sound correct??

Also i need to restrict the boudary of the DEM to another shapefile. It is just a single shape of the boundary of the field. Mostly all the data is there, however some interpolation will be needed.

Currently i am having trouble reading the file in using v.in.ogr.
command:
v.in.ogr ‘dsn=shapefile name’ output=elevation09 ‘layer=Elevation Map 9’
Result:
GRASS_INFO_WARNING Area size 9e…, area not imported
…
0 areas imported

THere are many columns in the .df file. How can i only import the ones i want? Clearly i have missed something.

Any help would be greatly appreciated.

THanks,
Ed

---------- Forwarded message ----------
From: quinonero juan manuel <jumaqu@yahoo.es>
Date: 25-Mar-2007 02:45
Subject: [GRASS-user] Creation of a DEM
To: grassuser@grass.itc.it

1.- You have to transform the vector information to a rast layer, you can do it using the comand v.to.rast, baut before you have to determine the cell resolution using for example g.region res=meters

2.- If you wsnt to create a good DEM you have to change the units of the rast layer created, Only have to convert this layer from meter to centimeter using r,mapcalc ‘cm_layer=rast_meter* 100.00’. That’s for obtain a good relation betwen horizontal and vertical resolution.

3.- Now you have to use an interpolatión method to create a DEM continous surface. There are several methods, the commonest is r.surf.contour tat use a lineal interpolation. If you use this command you must use the option -f and it’ll build faster, dont forget this point!!!

4.- Finally you have to transform the results to the correct units usin r.mapcalc ‘final_DEM=cm_DEM/100.00’

If you want to generate a DEM usin another interpolation methods please ask!!

Sorry for my english

Juanma

megha shyam < capt_lms@yahoo.co.in> escribió:

Please help me in creation of DEM.i have a vector layer contaning contour information.How to create a DEM model of this.Can you tell me the stpes to be followed

shyam

Here’s a new way to find what you’re looking for - Yahoo! Answers http://us.rd.yahoo.com/mail/in/yanswers/*http://in.answers.yahoo.com/ _______________________________________________
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Llamadas a fijos y móviles desde 1 céntimo por minuto.
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Michael Barton, Professor of Anthropology
Director of Graduate Studies
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton