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Home - General / All posts - New Video - Blend SRTM and Enhanced Bing Satellite
Dimitri


5,452 post(s)
#04-Mar-19 15:26

There's a new video in the Videos page, showing how to use the free Viewer to import SRTM, style, compute profile curvature, and then combine with a Bing satellite display that's been styled for extra contrast. Shows a number of useful tricks, like copying and pasting saved styles and queries from a Notepad .txt document.

Mike Pelletier


1,602 post(s)
#10-Apr-19 00:17

Is it possible to use 9 current tools to do an overlay blend of 2 rasters such as elevation curvature and a USGS topo raster? When blending them with just opacity settings the results are good but if we could use some fancy math and SQL to do these more involved blends that would be great. In the case of USGS topos, much of the image is a nice white and blending with opacity dulls the whole image.

tjhb

8,760 post(s)
#10-Apr-19 03:22

I haven't tried that Mike but that's a great idea.

Once the images are in a common tiling scheme, which may involve reprojecting one to the other, the maths is straightforward. It might be best to avoid the conditional, so that we get full CUDA processing. (To do that, we would work out both results for each pixel, then multiply by either 0 or 1, then add them. That is partly wasted work but I expect more efficient since it saves a trip back to CPU.)

It could even be done as a computed field, though that might be nuts.

Dimitri


5,452 post(s)
#10-Apr-19 06:08

Sure, should be straightforward.

As Tim has remarked, the blending is the easy part, as there are plenty of examples doing math on tiles and combining values. See the Examples topics in the images section for manipulating RGB images with matrix filters, for example.

The trickier part is the setup, where you want the two different rasters cut out to the same overall size and using the same sized tiles. I've done less of that, so I'm intimidated by it. :-)

As a thought experiment, suppose you have two different rasters but both the same overall size and same tile size. Take the table for one of them, where you have a Tile field, and bring in the other raster as a Tile2 field.

You now have both rasters in the same table and, using the examples for matrix filters as a guide, you can easily create a Tile3 field that is whatever mathematical blend you want of the Tile and Tile2 fields.

tjhb

8,760 post(s)
#10-Apr-19 07:53

The reprojection is not as hard as it looks. Adam has posted a couple of good examples here (replying to a question from Dan) and here (older, less directly helpful). The system really just deals with the hard stuff.

I like your idea to use Tile maths between multiple fields in the same table. Elegant and efficient.

Mike Pelletier


1,602 post(s)
#11-Apr-19 00:25

Thanks guys. I banged around on it a little but nothing good to share yet.

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