I am trying to extrapolate the precipitation data at some reference station within a DEM to each pixel of DEM. For this, i have longitudinal gradient. The longitudinal gradient is based on the horizontal distance. So i want to calculate the distance of each pixel of DEM with some reference pixel. How can i do this in R software? Is there any specific package for doing this?
Don't know what you mean by DEM, but I am thinking the following addresses your question:
https://cran.r-project.org/web/packages/geosphere/geosphere.pdf
It's really hard to say without knowing more about your data. In addition to Daniel Wright's response, the package "fields" has several distance calculation methods, including a simple Euclidean distance method, rdist(), and rdist.earth(), which will give you geographic coordinate distances.
Dear Daniel, here DEM stands for digital elevation model. Thank you Wright and Holstein for your suggestions.
Amrit - Just to let you know, if you want "actual" distances (meters, degrees, etc.) you will need to be sure that the pixels in your raster have geographic information associated with them. These would be available in your DEM.
Hi Armit,
make sure you use an adequate projected coordinate system (for example translate your scenes with GDAL or some GIS-program into e.g. UTM projection). Your distance in horizontal direction is then simply the distance (columns to the right or left) from your center pixel and its column.
So if you have your map in UTM with a pixel size "P" of 30m, and say the scene is represented by a "n x m"-matrix, where n is not important, and your starting point is in column "i":
Your horizontal distance to a point in column "j" from column "i" is: abs(j - i)*P
Make sure the x-spacing is equal at different northings (--> choice of projected coordinate system).
Good luck,
Eric
Dear Eric, I want to make a matrix of the distance between each grid of DEM and any point P(lon, lat, elv). Can i do this by following your instruction ?
Dear Jurgen,
Thank u for a solution. I have one more query. Can you explain me what is the coordinate system for a point. Is it (lon, lat) or something else?
Hi Amrit,
I had a look at distanceFromPoint that Jürgen mentioned. As it does not include elevation, I made a short script based on matrix-objects (not raster-objects) and Euclidean distance. You can bind the relevant passage into a function to calculate the distance matrices for multiple points. Hope you understand the code. The "fields"-package is only for visualisation.
Note:
- R's way to assign data to a matrix --> row/colomn-wise; you will find the attribute byrow=T.
- 'image.plot' and 'image' give you a transposed picture !
- no guarantee for correctness (I made it very quickly)
- make sure to have a proper projection (see Jürgen's and my first post) !
- make sure to set the right pixel resolution (variable "RES")
Best, Eric
Thank you Eric and Jurgen. i will go through your codes and let know if i get any problem.
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