I have big vector file with about 30000 points. Now I need extract values from ecological rasters for every of the vector points. Problem of the extraction is that some of raster cells includes more than 1 vector points. Using the standard module Extract in Idrisi and creating Definition Image I lose extractions for part of vector points if they are more than 1 points per raster cell. Is it mean that I can not extract values for every point of 30000 in Idrisi and need search other soft for this operation? - or Idrisi has alternative way for this kind of extraction?
Date
Votes
4 comments
-
Clark Labs My first thought is that you could create a higher resolution raster, so that multiple vector points don't fall into the same raster cells, but I realize that you could potentially have vector points with the same or almost the same coordinates, so that wouldn't be a solution.
My second thought is that we should add an option to use a vector file as an input, and extract the values directly from the vector coordinates instead of going through the intermediary of the raster point file - which is where you are losing your points. It's not that complicated of an operation to write, but it would take some time. I will write it up as a wish - to add that functionality to TerrSet. However, you probably need something more immediate.
There might be a way to do it in Database Workshop. If you converted the ecological rasters to vector polygon files (assuming that this would make sense for the type of data they contained), and using a combination of Create Display LInk, New Field, Query, Calculate Field Values... (Tutorial Exercise 1-9, E,F,G) I actually can't think about what steps it would take, and am not sure if it is possible. Perhaps I'm just having a mental block right now. The part I'm missing is how you get the database created in the first place...
If the Database Workshop idea doesn't pan out, I would suggest exporting the files to a different software, doing the vector Extract operation there, and then bring the data back.
-
Acer737 Thank you for response.
You are right – I have vector files from iNaturalist and they have a lot of points registration having the same or almost the same coordinates.
Also I tried to use Database Workshop for this operation. But in simple direct way it demands the same Feature Definition Image. As touch conversion ecological raster to vector – it is impossible for rasters similar global Modis mod11C3 – after 3 minutes converting Idrisi said me: “Not enough memory for processing”.
Now I have solved this task in QGIS module Sample Raster Values. It would be great if you implement your second thought to add an option to use a vector file as an input, and extract the values directly from the vector coordinates instead of going through the intermediary of the raster point file. As I see - this module design could be like the Extract module. -
Clark Labs I agree. It would be a very useful addition to the Extract Module. I'll put in a wish request and flag this conversation, so that I could let you know if it is implemented.
-
Acer737 Great! Let me know.
Please sign in to leave a comment.