How to create a polygon from a large raster file?

How to create a polygon from a large raster file?

I have a large raster file (5GB) containing only 1’s and NA’s. I would like to convert this into a multipolygon of the areas with 1’s, with adjacent cells dissolved into one polygon.

How do you extract data from raster in R?

Rather than select a single value, we will create a circular BUFFER around each point and then extract raster values that fall within that circle. Finally, we will calculate a mean of all pixels values to create a final value. The default option when we extract data in R is to store all of the raster pixel values in a list.

How to plot raster values in R-open?

In this segment of the lesson, we will use a set of points. At each point we will extract raster values from a buffer region around that point and calculate a summary stat (in this case a mean raster value). We will then plot the points on a map weighting the size according to relative mean value.

Is it possible to avoid reprojecting raster data?

Generally I try to avoid reprojecting raster data if at all possible. In this case, let’s reproject our raster data because we are working with a relatively small area (relative to the globe) and we are only extracting values from the data – we won’t be using it for further processing steps. Generally i’d prefer to reproject the vector data.

How to create a rectangular extent in QGIS?

For the rectangular extent, just use the “Tile Index” under Raster > Miscellanious > Tile Index. If you don’t see the Raster menu, you may have to install or enable the GDALTools plugin. And of course if you aren’t tied to doing it in QGIS, you could just use GDAL directly.

How to convert raster to points in ArcGIS?

If you don’t have Spatial Analyst you can do it anyway as follows: First, convert the raster to Points using the Raster to Pointtool. This gives you a grid of points and is relatively quick – 16million points were created in about 2 minutes (be sure to turn off rendering so they aren’t displayed though 😉 ).

How to create a polygon from the extent of an image?

If you want only the extent of one image and not the full directory you can go to Vector->Research Tool->Polygon from layer extent here select the image you want the extent and save the output.

How to convert raster to smooth contour polygons?

I exported a Raster to a Vector and try to and use v.generalise and I get mostly smooth polygons with the occasional ‘stepped’ boundary which appears to have been unaffected by the algorithm. I found a process that worked for my task, not sure if its the best way but thought i’d share it in case it helped you.

How to generalize and vectorize a Rasterfile?

I want to vectorize that rasterfile with its 6 landuse classes. The classification is very noisy and have to be generalized before. The result should be a polygone vector file. I use SAGA, (GRASS) and QGIS. To simplify the raster it might be worth looking at gdal_sieve, it’s available under the “Raster” menu.

How to generalize and vectorize a GRASS GIS?

You can first use the “mode” operator of r.neighbors in GRASS GIS (via Sextante plugin), then vectorize with r.to.vect to obtain polygons. Perhaps the “mode” operator should be run more than one time. Using the majority filter with a kernel of 5 by 5 pixels gives the best results for me.