Tarsier tutorial: Raster resampler

What is raster re-sampling?

Raster data are gridded data, where the grid usually represents geographic space, and the values in the grid usually represent geographic properties at locations specified by the grid.

Raster grids can be specified with different locations, different cell sizes (different resolutions), and different geographic projections (e.g. Geographic (lat/lon), UTM, GIH, State plane, etc.).

To convert raster data from one grid to another, re-sampling is required. This involves, estimating a value for each cell in the new grid based on one or more nearby values from the old grid. It always involves a change in the accuracy (usually a reduction in accuracy) with which the raster data represents the actual property of interest, because of the inherent changes in resolution, or blurring of information across cell boundaries. So, re-sampling should be done as infrequently as possible.

Pre-requisites for this tutorial?

• Tarsier tutorial: Raster data

How do you re-sample a raster in Tarsier?

1. Open Tarsier
2. Select File --> New --> Tools --> Raster re-sampler (if its not on the list, you need to load a DLL)
3. You should see a RasterResample window with some options and a number of UseeControls.
4. The basic process in re-sampling is to convert the values in input raster to values in an output raster using the template raster to specify the spatial grid to be used in the output raster.
5. First, you should specify an input raster. Use its UseeControl to select an already-loaded raster (drop-down arrow) or open one from file ('Open').
6. Next, you should decide if you have and want to use a template raster. If you don't, one will be automatically created for you.
   1. If you want to use a template raster, specify it using the Template raster UseeControl
7. Now, you're ready to execute the re-sampling.
   1. If you're using a template raster, click the button at top-left with an icon that looks like cogs.
   2. If you're letting a template be created for you, click the button that says 'Auto-create...'
8. Finally, you can view you raster. Click View on the output raster's UseeControl
   1. To change how it looks, see the tutorial for raster data
9. We're not quite done, you'll want to save not only your new raster, but also the resampler, so that you know how you made your raster and you can do it again if you need to.
   1. Recall that saving files in Tarsier is a bit idiosyncratic.
   2. Select the re-sampler window
   3. Select Save As from the menu
      1. A number of dialog boxes will appear one by one, each one asking you if you want to save one of the many files that the re-sampler uses, or the re-sampler file itself (TRP).
      2. The first dialog pertains to the input raster. Its probably already saved, so just type ESC to quit saving it again.
      3. The files you do want to save are probably just the output raster (TRA) and the re-sampler file (TRP) which lists all the files and options used in the re-sampling.
      4. Hit ESC on any files you do not want to save.
10. If you ever want to re-do or modify this re-sampling, just open the TRP file.
11. Also, if you change anything, and you want to make sure its saved before you move on, you can always select File --> Save -- Save All Named (which covers everything except what's contained in default objects that Tarsier created for you but that you have not yet named (by saving), such as 'Raster Data 1').

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Next

• You could try Tarsier tutorial: Renderer

Links

• Other Tarsier Tutorials