Latest Contributions by PawanThapa

‎07-26-2019

Any hint please?

‎07-26-2019

Oh yes. Thanks a lot. I get it done correctly by splitting the workflow in the expression as suggested by Curtis Price. Great help. Cheers!

‎07-26-2019

Thank you very much for your suggestion. I think I understand it correctly and looks like it produce teh resultst hat i want in such straight forward way - but knowing only after you have mentioned it. But somehow when I copied the "expression" given by you in the raster calculator window--it shows error and doesnot run further..why can it be? I have changed the "dem" with my dem file name..rest i use as it is written by you. Do not know what t odo with the terms "Value" and "Area" in your expression..i leave as it is in my expression--and it does not run.

‎07-24-2019

Dear Experts, Working on a DEM (30m x 30m raster) of a large area, I need to find out the area (polygons) which is greater that 5,000 hectares and within which average slope is less than 10 degree. The shape of the area/polygon- more it is towards square or reactangle better it is. I cannot figure out which step would enable me to achieve this. Can you experts guide me or give me hint, please?

‎07-24-2019

Dear Experts, I'm using ArcGIS 10.6.1. I have a polygon shape file along a river stretch (represents maximum flooding area) and a DEM (30m x 30m raster) reperesnting the eelvation in and around the area. Now what I need is to extend that boundary-polygon or buffer it towards outside (from the riverline on both sides/banks) such that the new boundary polgon is away from earlier boundary polygon by 3meter increase in elevation (based on the udnerlying DEM) - which means in vertical cliff both boundary line will be same, in high slope the new boundary line will be little further away and in flat slope it will be much furtehr away. I hope I could make my task clearer. Hoping for the hints from the expert on how to get this done? Thanking you all!

‎07-22-2019

Dear Experts, I'm using ARcGIS 10.6.1, wit hspatial and 3D analyst (not full license) I have a polygon shape file along a river stretch (represents maximum flooding area) and a DEM (30m x 30m raster) reperesnting the eelvation in and around the area. Now what I need is to extend that boundary-polygon or buffer it towards outside (from the riverline on both sides/banks) such that the new boundary polgon is away from earlier boundary polygon by 3meter increase in elevation (based on teh udnerlying DEM) - which means in vertical cliff both boundary line will be same, in high slope the new boundary line will be little further away and in flat slope it will be much furtehr away. I hope I could make my task clearer. Hoping for the hints from the expert on how to get this done? Thanking you all!

‎07-16-2019

Dear Experts, I'm using ArcGIS 10.6.1. with spatial analyst and 3D analyst only Working on a DEM (30m x 30m raster) of a large area, I need to find out the area (polygons) which is greater that 5,000 hacters and within which average slope is less than 10 degree. The shape of the area/polygon- more it is towards square or reactangle better it is. I cannot figure out which steps would enable me to achieve this. Can you experts guide me or give me hint, please? Best Regards, Pawan Thapa

‎10-09-2017

Forgot to mention, but as already said--how I was doing--- I use focal statistics to calculate minimum with 5km search radius over the river DEM and i subtract the original RivDEM with the result of the focal statistics. The problem here is, in that search radius of 5km, for several cells of RiverDEM it found the minimum at adjacent rivers instead of in the same river downstream, which in reality is at another side of the mountain ridge, hence giving me unwanted results. When the adjacent rivers are more than 5km away, then the results are ok but that will not be the case everywhere, mainly toward confluencing or branching of the rivers....

‎10-09-2017

Dear Xander, Thanks a lot. I have extracted a small area from my working-region as a sample data and attached herewith. But these are two raster grids-- one-RiverDEM showing Elevation value at each cell (30m X30m) and another-Flowdir showing at each cell its flow direction to next cell (standard D-8 algorithm of flow direction in GIS). At this location of sample data as well, I had that problem while trying to find the elevation difference (Head) for each river cell in a 5km river stretch from that each river cell. I hope this gives you now further clearer info about my need/problem. Thanks a lot!

‎10-09-2017

Dear Dan, Thank you for the suggestion. But main problem with the array calculation as you have suggested is, as far as I have understood- it does not follow the flow direction from the calculating cell to the end cell (2nd, 3rd etc.. or 166th cell for 5km elevation difference --my raster is 30m x 30m..), which will become problem when there are several branching rivers/tributaries within that 2-5 km distance conflencing towards a main river-- -- or am I missing or misunderstanding something in your suggestion?

‎10-06-2017

Thanks Xander for the reply/ suggestion ..... So far I could not find solution through ArcHydro as well .. I was thinking somehow I could use flow direction map as well in combination to find appropriate solution method doing in raster but could not find a way out. I think I have to learn Python for this (time-permitting for this quick job) -- I know only FORTRAN programming- quite old..

‎10-06-2017

Sure Dan, let me give more insight on my goal to obtain exact solution so far as possible. I'm doing this work in the field of "mapping the hydropower potential" in the river network of a country. Aim is to show the hydropower potential in each river cell of the river network (which is 30m X 30m from SRTM-DEM) , when the waterway (or powerhouse) is kept at, say 5km below/downstream from that river cell in the same river. So, the calculation should successively move down cell by cell, each time/cell calculating the elevation difference between that cell and the cell 5km downstream, through all river network. As obvious the power potential at a river cell is function of the product of flow and elevation head at that cell (Head is the elevation difference between that considered cell and the cell in the same river 5km downstream). Through hydrological analysis and GIS, I have river raster with flow values at each river cell; and now remains to be calculated is a river raster where each river cell is showing the elevation head for that 5km river stretch downstream starting from that river cell. This is where I'm getting stucked. I hope I could make my problem and aim clearer to you!

‎10-06-2017

Dear GIS experts, I would be very thankful to receive your help/support/suggestion for solving my following problem. I'm using ArcGIS 10.1 with Spatial Analyst and 3D Analyst(no ArcInfo license) and Arcview 3x (still for many plusses). I have a river network - both a shape file and raster grid - generated from a DEM through Flow Direction and Flow Accumulation grid for a very big region (a country). What I want to know/calculate is - for every river cell, what is the difference in elevation value between the elevation of that river cell and the elevation of the river cell at a given distance (say, 1 km, 2km, 5km) downstream from that river cell along that river i.e. flow direction? I tried to do this by using the focal statistic function running over the River-DEM (using minimum as statistic) and then subtracting the resulting grid from the original River-DEM; but this dos not work completely correctly because at many places the minimum in the neighbourhood is found in the adjacent river (tributary or another parallel river at another side of the ridge) and it gives me wrong elevation difference because the minimum river cell is not in the same river downstream but in another river although within the defined search/neighbhourhood distance. How can I get this correctly- i.e. the elevation difference in the same river downstream in a given distance? I hope that I could make this my problem sufficiently clear. What would be your suggestion to solve this? Thanking you a lot!!

‎06-20-2017

Dear Dan, I did not know how to close teh earlier post and so following your suggestion i reposted my query in this another thread. To extract values from the 5 rasters to my main raster (which has few identified hot spots of few successive cells at many places), as you have sugessted I first tried to convert the hot-spots raster to points, but after some processing it stops with 2GB shapefile limit and I'm stucked there as I think without having shape file I cannot have teh required table. How to tackle? Please suggest..

‎06-20-2017

Dear experts, I would be very thankful to receive your help/support/suggestion for solving my following problem. I'm using ArcGIS 10.1 with Spatial Analyst and 3D Analyst(no ArcInfo license) and Arcview 3x (still for many plusses). I have a raster file- 30m X 30m River netwok cells. I have identified some hot spots i.e. few consecutive river cells at different locations. On the other hand, I have 5 rasters (same as river network) having unique value in each of these rasters. Now, what I need is the value of these 5 rasters at the location of the hot-spots (the identified few consecutive river cells) in a tabular form. i.e. a table which gives me the location of these hot spot cells (even one central location is ok) and the coressposnig value at these locations from the 5 rasters. How can I do this? Your suggestion is highly appreciated. Many Thanks! pawan

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Latest Contributions by PawanThapa

Re: Buffer a polygon based on a raster

Re: DEM to Polygon

Re: DEM to Polygon

DEM to Polygon

Buffer a polygon based on a raster

Buffer polygon based on Raster

Query on Topographic Analysis

Re: How to find Elevation difference along the river line?

Re: How to find Elevation difference along the river line?

Re: How to find Elevation difference along the river line?

Re: How to find Elevation difference along the river line?

Re: How to find Elevation difference along the river line?

How to find Elevation difference along the river line?

Re: Extracting values from rasters in a table

Extracting values from rasters in a table