I have downloaded Cartosat DEM recently and want to do features extraction from it. I could not get any step by step tutorial for this. I can use ArcGIS and to some extent Erdas imagine. Can you enlighten me please?
In spatial analysis of ArcGIS:
Fill all sinks in your DEM using the Fill tool.
a. Set the Input surface raster to dem2m.
b. Set the Output surface raster to be dem2mfill.
c. Leave the Z limit blank. (This is where you
would set a fill limit if desired.)
d. Click OK.
Calculate flow accumulation using the Flow Accumulation tool.
Your flow accumulation layer is added to the map, and represents the amount of water that would flow into each cell, assuming that all water became runoff and there was no interception, evapotranspiration, or loss to groundwater. This could also be viewed as the amount of rain that fell on the surface, upslope from each cell. Basically, the flow accumulation tool counts the number of cells that are flowing into it:
• Cells with a high flow accumulation are areas of concentrated flow and may be used to identify stream
channels.
• Cells with a flow accumulation of zero are local topographic highs and may be used to identify ridges.
In the resulting flow accumulation raster dataset white areas are cells with very high flow accumulation
(areas of concentrated flow), and can be used to identify stream channels.
Create a stream network raster using your flow accumulation grid:
a. Turn on the Spatial Analyst toolbar by going to the View menu > Toolbars > Spatial Analyst. In addition, go to the
Tools menu > Extensions, and make sure that Spatial Analyst is checked on.
b. In the Spatial Analyst toolbar drop-down menu, choose the Raster Calculator.
c. In order to create a stream network, you will need to specify a threshold for how many adjacent stream pixels make up a stream. Here we will specify a threshold value of 2000 pixels of accumulation (any pixel with more than 2000 pixels flowing into it will be part of the stream network).
d. Type in the blank area of open menu: streamnetwork = con([fillflowacc] > 2000, 1)
e. Click Evaluate.
The stream network raster will be added to your map.
Create a stream link raster using the Stream Link tool.
a. Set the Input stream raster to be streamnetwork.
b. Set the Input flow direction raster to be fillflowdir.
c. Set the Output raster to be streamlink.
d. Click OK.
The stream link raster is added to your map.
Create a stream order raster using the Stream Order tool.
a. Set the Input stream raster to be streamnetwork.
b. Set the Input flow direction raster to be fillflowdir.
c. Set the Output raster to be streamorder.
d. Set the Method of stream ordering to be either STRAHLER or SHREVE.
e. Click OK.
The stream order raster is added to your map. The stream ordering you choose is dependent on what kind of method you want to use.
Create a stream shapefile using the Stream to Feature tool.
a. Set the Input stream raster to be streamnetwork.
b. Set the Input flow direction raster to be fillflowdir.
c. Set the Output polyline features to be stream2000simp.shp (“simp” stands for simplify)
d. Check Simplify polylines
e. Click OK.
The stream shapefiles is added to your map.
Create a basins raster using the Basin tool.
a. Set the Input flow direction raster to be fillflowdir.
b. Set the Output raster to be basin.
c. Click OK.
The basins raster is added to your map.
Using the Watershed tool directly on the stream gages as pour point data, it is necessary due to certain problems to use the Snap Pour Points tool to first snap our pour points (streamgages.shp) to nearby areas of high flow accumulation.
Snap the pour points (streamgages.shp) to areas of high flow accumulation using the Snap Pour Points tool.
a. Set the Input raster or feature pour point data to be streamgages.
b. Set the Pour point field to be SITENO.
c. Set the Input accumulation raster to be fillflowacc.
d. Set the Output raster to be snappourpoint.
e. Set the Snap distance to be 175, since that is the approximate maximum distance the a stream gage from a major stream (as delineated by our streamnetwork2000.shp dataset).
f. IMPORTANT- Click on Environments, and under General Settings, set the Extent to Union of Inputs. This is absolutely necessary for all the snapped pour points to fall exactly on the streams (otherwise, those points won’t search outside the input extent, which oftentimes doesn’t include areas where the streams actually are)
g. Click OK.
Create a watershed raster using the Watershed tool.
Watersheds can be delineated two ways with the Hydrology Tools:
• Raster: This is either a result from the Snap Pour Point tool, or another raster that you have created, with No Data cell representing areas for pour points.
• Shapefile: This is a shapefile or other feature class that represent pour points; however, problems in watershed delineation (tiny watersheds) result if the points are not in areas of high flow accumulation (in or near stream channels).
a. Set the Input flow direction raster to be fillflowdir.
b. Set the Input raster or feature pour point data to be
snappourpoint.
c. Set the Pour point field to be Value.
d. Set the Outpur raster to be watershed.
e. Click OK.
The watershed raster is added to your map.
Calculate flow length upstream and downstream using the Flow
Length tool.
Using the Flow Length tool, the length of the flow path, either
upslope or downslope, from each cell within a given watershed can
be determined. This is useful for calculating the travel time of water
through a watershed.
UPSTREAM calculates the longest upslope distance along the flow
patch, from each cell to the top of the drainage divide, or ridge.
a. Set the Input flow direction raster to be fillflowdir.
b. Set the Output raster to be upstream.
c. Set the Direction of measurement to be UPSTREAM.
d. Click OK.
The upstream flow direction is added to your map.
DOWNSTREAM calculates the downslope distance along the
flow path, from each cell to a sink or outlet on the edge of the
raster.
e. Set the Input flow direction raster to be fillflowdir.
f. Set the Output raster to be downstream.
g. Set the Direction of measurement to be
DOWNSTREAM.
h. Click OK.
The downstream flow direction is added to your map.
Save your ArcMap project, and close ArcMap.
Download is available at
http://bhuvan-noeda.nrsc.gov.in/download/download/download.php
Cartosat-1&2 data provide along track stereo data continuously with their fore and aft cameras. 10 bit quantization and near real time imaging between the stereo pairs which improve the image matching accuracies. Stereo data along with Rational Polynomial Coefficients (RPCs) provides an opportunity for photogrammetric processing for DEM and ortho image generation. Selection of a suitable number of Ground Control Points and polynomial order for the refinement of Rational Polynomial Coefficients can form a basis for generating an accurate Digital Elevation Model (DEM). To retrieve the terrain parameters such as slope, aspect and drainage network, comparative evaluation of the drainage order even boundaries between plots can be extracted from the DEM so developed.
The role of the Ground control points (GCPs) is to effect an image coordinate translation and thus their location within the scene is of no real consequence; addition of further GCPs makes no contribution to the geometric strength of the triangulation process per se. Instead the extra control points simply provide more information from which to evaluate an appropriate ‘average’ image coordinate correction. Nevertheless, with the use of redundant control points one can be more confident about the reliability of the geopositioning process.
Generally, there is no important difference between polynomials models of different orders to improve RPC derived coordinates of Cartosat-1 stereo images. Even, with 0th order polynomial (one translation), accuracies of 2 m. in horizontal and of 4 m. in vertical can be achieved. It is understood that RPCs of Cartosat-1imagery contain mostly translation errors. Because using one GCP is prone to errors of GCPs used for calculation, it is recommended that using one more GCP is enough for most of the applications. But it is more robust to use 1st order polynomial, although it needs more GCPs. Also, the distribution of the GCPs is of no importance. Although 2nd order polynomial provides also good results, it requires more GCPs and sensitive to GCP configuration. Because the precision and accuracy of the GCPs are so high (0.5 m.), it is inferred that the errors come from the GCPs measurement (0.5-1 pixel) on the images.
The radiometry of Cartosat-1 & 2 Images are very good and suitable for mapping
• Comfortable stereo viewing & effective image matching
• No Streaking, banding, saturation, noise and other radiometric artefacts
• Independently processed scenes align at sub-pixel level and are well suited for mosaicing. The RPC model with GCPs provides the positional accuracy within one pixel and DEM accuracy 4m.
• Combination of C-1 & C-2 images provides the vital information for feature extraction and mapping:
2D Features: Roads with Trees, National Highways, City Roads and Streets, Cart Tracks, Railway Lines, Railway Lines under Construction, Roads under Construction, Permanent Streams and Rivers, Temporary Streams and Rivers, Rivers with Trees, Canals, Lakes, Tanks, Village Ponds, Delimitation of Vegetation Cover, Pastures/Grazing Lands, Forests, Agricultural Fields, Plots and the likes.
2D &3D Features: Individual Buildings and Blocks of Buildings, Village Houses, Stadium, Aerodrome, Railway Stations, Industrial Estates and the likes.
The methodological steps shown the attached flowchart may be employed to this effect:
@ Mohammad Firoz Khan
Thank you sir for ur suggestion. But as I'm a newbie in RS/GIS field, can u plz tell me how to process DEM in ARCgis. The flowchart makes sense, but still need a "how to" guide or tutorial. I have search on net for tutorial but in vain.
Dear Sachin Patil
Please specify exactly which features do you want to extract from CARTOSAT DEM whether topographic or hydrological?
Dear sir I want to extract hydrological data from CARTOSAT DEM.
How can do this
In spatial analysis of ArcGIS:
Fill all sinks in your DEM using the Fill tool.
a. Set the Input surface raster to dem2m.
b. Set the Output surface raster to be dem2mfill.
c. Leave the Z limit blank. (This is where you
would set a fill limit if desired.)
d. Click OK.
Calculate flow accumulation using the Flow Accumulation tool.
Your flow accumulation layer is added to the map, and represents the amount of water that would flow into each cell, assuming that all water became runoff and there was no interception, evapotranspiration, or loss to groundwater. This could also be viewed as the amount of rain that fell on the surface, upslope from each cell. Basically, the flow accumulation tool counts the number of cells that are flowing into it:
• Cells with a high flow accumulation are areas of concentrated flow and may be used to identify stream
channels.
• Cells with a flow accumulation of zero are local topographic highs and may be used to identify ridges.
In the resulting flow accumulation raster dataset white areas are cells with very high flow accumulation
(areas of concentrated flow), and can be used to identify stream channels.
Create a stream network raster using your flow accumulation grid:
a. Turn on the Spatial Analyst toolbar by going to the View menu > Toolbars > Spatial Analyst. In addition, go to the
Tools menu > Extensions, and make sure that Spatial Analyst is checked on.
b. In the Spatial Analyst toolbar drop-down menu, choose the Raster Calculator.
c. In order to create a stream network, you will need to specify a threshold for how many adjacent stream pixels make up a stream. Here we will specify a threshold value of 2000 pixels of accumulation (any pixel with more than 2000 pixels flowing into it will be part of the stream network).
d. Type in the blank area of open menu: streamnetwork = con([fillflowacc] > 2000, 1)
e. Click Evaluate.
The stream network raster will be added to your map.
Create a stream link raster using the Stream Link tool.
a. Set the Input stream raster to be streamnetwork.
b. Set the Input flow direction raster to be fillflowdir.
c. Set the Output raster to be streamlink.
d. Click OK.
The stream link raster is added to your map.
Create a stream order raster using the Stream Order tool.
a. Set the Input stream raster to be streamnetwork.
b. Set the Input flow direction raster to be fillflowdir.
c. Set the Output raster to be streamorder.
d. Set the Method of stream ordering to be either STRAHLER or SHREVE.
e. Click OK.
The stream order raster is added to your map. The stream ordering you choose is dependent on what kind of method you want to use.
Create a stream shapefile using the Stream to Feature tool.
a. Set the Input stream raster to be streamnetwork.
b. Set the Input flow direction raster to be fillflowdir.
c. Set the Output polyline features to be stream2000simp.shp (“simp” stands for simplify)
d. Check Simplify polylines
e. Click OK.
The stream shapefiles is added to your map.
Create a basins raster using the Basin tool.
a. Set the Input flow direction raster to be fillflowdir.
b. Set the Output raster to be basin.
c. Click OK.
The basins raster is added to your map.
Using the Watershed tool directly on the stream gages as pour point data, it is necessary due to certain problems to use the Snap Pour Points tool to first snap our pour points (streamgages.shp) to nearby areas of high flow accumulation.
Snap the pour points (streamgages.shp) to areas of high flow accumulation using the Snap Pour Points tool.
a. Set the Input raster or feature pour point data to be streamgages.
b. Set the Pour point field to be SITENO.
c. Set the Input accumulation raster to be fillflowacc.
d. Set the Output raster to be snappourpoint.
e. Set the Snap distance to be 175, since that is the approximate maximum distance the a stream gage from a major stream (as delineated by our streamnetwork2000.shp dataset).
f. IMPORTANT- Click on Environments, and under General Settings, set the Extent to Union of Inputs. This is absolutely necessary for all the snapped pour points to fall exactly on the streams (otherwise, those points won’t search outside the input extent, which oftentimes doesn’t include areas where the streams actually are)
g. Click OK.
Create a watershed raster using the Watershed tool.
Watersheds can be delineated two ways with the Hydrology Tools:
• Raster: This is either a result from the Snap Pour Point tool, or another raster that you have created, with No Data cell representing areas for pour points.
• Shapefile: This is a shapefile or other feature class that represent pour points; however, problems in watershed delineation (tiny watersheds) result if the points are not in areas of high flow accumulation (in or near stream channels).
a. Set the Input flow direction raster to be fillflowdir.
b. Set the Input raster or feature pour point data to be
snappourpoint.
c. Set the Pour point field to be Value.
d. Set the Outpur raster to be watershed.
e. Click OK.
The watershed raster is added to your map.
Calculate flow length upstream and downstream using the Flow
Length tool.
Using the Flow Length tool, the length of the flow path, either
upslope or downslope, from each cell within a given watershed can
be determined. This is useful for calculating the travel time of water
through a watershed.
UPSTREAM calculates the longest upslope distance along the flow
patch, from each cell to the top of the drainage divide, or ridge.
a. Set the Input flow direction raster to be fillflowdir.
b. Set the Output raster to be upstream.
c. Set the Direction of measurement to be UPSTREAM.
d. Click OK.
The upstream flow direction is added to your map.
DOWNSTREAM calculates the downslope distance along the
flow path, from each cell to a sink or outlet on the edge of the
raster.
e. Set the Input flow direction raster to be fillflowdir.
f. Set the Output raster to be downstream.
g. Set the Direction of measurement to be
DOWNSTREAM.
h. Click OK.
The downstream flow direction is added to your map.
Save your ArcMap project, and close ArcMap.
@ Kuldeep
Thank u sir,
this is the most detailed procedure I could get on net.
It helped.
btw I came across module in qgis which does it all but output are in raster format.
Satish the threshold values vary according to terrain type or area likely to be drained. Generally in ASTER DEMS threshold values are 25 cells for head waters in the mountain areas, 50-100 for pediments, 100-250 for Alluvial fans and 500 and more cells for plain areas.
@ Mohammad Firoz Khan sir.
I have a question regarding Cartosat-1 stereo orthokit (mountainous area).
Product is in geotiff format (band a and band f ) which is already in geographic coordinates as it is provided by NRSC, but i think they are roughly georefrenced because i am not able to fit those bands one upon another.
Now my questions are:
1 There is a need to georefrence the data again? or we should remove the georefrencing properties which are attached to the data at the time of delivery by NRSC.
2 How to execute georefrencing effectively for the stereo pairs (mountanious area) that both the pairs will stick together properly. Before going to genrate DEM to extract landslide.
Can anybody tell me from where I can download cartosat DEM data? Is it freely available?
@ Rucha
Yes, it is absolutely free. you can download it from..
http://bhuvan-noeda.nrsc.gov.in/download/download/download.php
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