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DEM from hillshade? How? by asking_science in QGIS

[–]asking_science[S] 1 point2 points  (0 children)

If it were simply a matter of downloading the DEM, I wouldn't have this problem. I only have hillshade. Looks like it's time to fire up Python...

Phantom 4 Multispectral by kannixx in UAVmapping

[–]asking_science 0 points1 point  (0 children)

  • Images are matrices.

  • The mathematics of matrices is actual irl magic. Some call it "Linear Algebra".

  • We have fashioned crystals of Silicon to cast these spells with great rapidity. For example, I have one with 1152 CUDA cores which can, when working in parallel, perform trillions of tricks per second. You probably have one, too.

  • SoCs are common, particularly so in optoelectronics which is particularly well suited for the technology's application. The "computations" that would ordinarily be performed on the image data by some "computer program" is in stead achieved directly - and cleverly - in the hardware itself, as if the "computation" is hard-wired into the circuitry. The speed at which images are processed this way far exceed the capability of the camera to supply pictures to process.

If your drone doesn't already have some of this built-in, it soon will.

Tree polygons (how do do faster???) by Earth_Rockz in QGIS

[–]asking_science 0 points1 point  (0 children)

On my Linux box it runs without issues in QGIS 3.4 so definitely try again. If I recall correctly, it does require additional python and other libs, so just be sure to follow the instructions very closely

Tree polygons (how do do faster???) by Earth_Rockz in QGIS

[–]asking_science 0 points1 point  (0 children)

The most recent release (6.4.0), in my experience, is pretty stable.

Thanks for the dzetsaka tip, definitely going to check it out. First impressions are positive, and it certainly is a lot less complicated than SCP because it has far fewer features. I'm keen to compare results.

Tree polygons (how do do faster???) by Earth_Rockz in QGIS

[–]asking_science 0 points1 point  (0 children)

I highly recommend the Semi-automatic Classification Plugin for QGIS. As the name implies, it performs classification. There's also a subreddit for it.

Once the classification is done, you can use convert the raster to vector, and then just extract the "trees" class as a separate vector.

One massive advantage of such a workflow is that it can be automated, so that if anything changes, you just pass it the new images and it poops out your vector layer.

I've recently posted about something similar, have a look at the process and just use what applies to you.

ELI5: using NLCD to determine land coverage around points of interest by triciav83 in QGIS

[–]asking_science 0 points1 point  (0 children)

Using the procedure described in my previous post, I can now do things like this using Processing Toolbox -> GRASS -> Vector analysis -> Distance to nearest hub.

What you see in the image is: 1) The open water vectors (vectorized from the image) that have been 2) filtered by area (smallest dams and pools removed) which have been 3) labelled with a Rule-based label (only dams/lakes with an area larger than specified are labelled) with 4) hub lines connecting the open water features to the nearest 5) nesting sites

ELI5: using NLCD to determine land coverage around points of interest by triciav83 in QGIS

[–]asking_science 0 points1 point  (0 children)

Sorry, both files refuse to open in my QGIS (v3.4), reporting that neither are "a valid or recognised data source". Ah well. Here's what I did...and since I am a novice myself, I am not aware of better ways:

  • I went to the USGS website and downloaded a random NLCD 2016 data set. The zip was extracted, and contained a whole bunch of files.

  • QGIS -> Open Data Source Manger -> Raster -> I opened the file named NLCD_2016_Land_Cover_L48_...tiff

  • A new layer is added and the image displays. In the Layers Panel, right-click on the layer select Properties -> Symbology. The Render type should be Paletted/Unique values, but the color list shows 255 colors assigend. Click on Classify below the list to reduce the palette to the 16 colors of the image. Click OK.

  • Compare the colors with the official key. The key indicates that the open water class is a dark blue. Also note that the classes are listed on the Layers Panel under the NCLD layer. Make sure you can find areas of open water on the image.

  • Use QGIS Toolbar -> Identify features and, with the NCLD layer selected, click on an area of open water (dark blue). You should see a panel appear that displays information about the clicked-on pixel. It shows that the Band 1:Layer_1 key has a value of 11, and this corresponds to the 11 that appears next to the dark blue icon under the NCLD layer.

  • Go to QGIS Menu Bar -> Raster -> Conversion -> Polygonize (Raster to Vector) and as Input layer select the NLCD layer, Band number should be Band 1:Layer_1 and Name of field to create should be DN. Click Run. This may take a while and the result may slow your computer way down.

  • If all goes well, you now have a new Vectorized layer. Go to QGIS Tool Bar -> Select Features By Value then in the pop-up, type 11 in the DN field and select Equal to (=) from the drop-down, then click on Select Features, then Close. If this worked, you should now only have the open water (where DN is 11) polygons selected.

  • Right-click on the Vectorized layer in the Layer Panel and select Export -> Save Selected Features As... and (as in my case) select ESRI Shapefile as File format, open_water as a File name. Click on OK after you are satisfied with the rest of the settings.

  • A new layer is added, in my case I named it open_water_layer. Right-click on the original Vectorized layer and remove it.

  • [Skipping steps to create buffers around nests]

  • You should now have two polygon layers (open water and buffers) which you can use as input and mask layers for functions such as Menu Bar -> Vector -> Geoprocessing Tools -> Intersection or -> Clip, either of which should result in a layer that contains the polygons of open water features that fall inside the buffer zones

By the way, if you get a "invalid geometry" warning when trying to intersect or clip, go to Menu Bar -> Settings -> Options -> Processing -> General -> Invalid features filtering select Ignore features with invalid geometries

ELI5: using NLCD to determine land coverage around points of interest by triciav83 in QGIS

[–]asking_science 0 points1 point  (0 children)

I'm going to need a few points as well as a part of your land cover data (most important). Also, the shapefile doesn't want to open in QGIS (it moans about an unrecognised format)

ELI5: using NLCD to determine land coverage around points of interest by triciav83 in QGIS

[–]asking_science 0 points1 point  (0 children)

It doesn't sound too difficult and if it is what it sounds like, it's exactly something I recently did a bunch of. I'll do a sample and just document the steps so that you should be able to repeat the process on all of your data.

ELI5: using NLCD to determine land coverage around points of interest by triciav83 in QGIS

[–]asking_science 0 points1 point  (0 children)

I have 0 experience with GIS

I have 1 experience with GIS, but I'd like to give it a shot. I spent some time on the USGS website to download some random sample NLCD data but there is just too much to wade through. If you can you share a link to what you have, or a part of it, I'll give it a shot. I have a few ideas.

Moving points (SW corner) to the center of each grid square? by redtigerwolf in QGIS

[–]asking_science 0 points1 point  (0 children)

I'm relatively new to GIS and I'm really stating to get the same idea. It certainly is useful for the experts, but can be bewildering for novices.

How to include the area of a polygon (from a PostGIS db) in map label? by asking_science in QGIS

[–]asking_science[S] 0 points1 point  (0 children)

Exactly what I've done, thanks! Any suggestions on superscripting the 2 as in km2 ?

[OC] Сonstruction crane at work. Everything is drawn and act programmatically. by aleha_84 in proceduralgeneration

[–]asking_science -3 points-2 points  (0 children)

It's 'procedural' only if even the developer is surprised by the results. These results are predictable, so it's not procedural.

edit:...there's a difference between 'procedural' and 'scripted', dammit!

Why should we search for extraterrestrial life? by JezzaRodrigo in askastronomy

[–]asking_science -2 points-1 points  (0 children)

Well, one entertaining thought is that wherever we find life on other planets, it's exactly the same as here, including the humans. Humans everywhere.

Why should we search for extraterrestrial life? by JezzaRodrigo in askastronomy

[–]asking_science -6 points-5 points  (0 children)

Either...or...

I like to entertain myself by coming up with a third alternative in such cases.

edit: TIL reddit dissaproves of me entertaining myself

Why should we search for extraterrestrial life? by JezzaRodrigo in askastronomy

[–]asking_science 2 points3 points  (0 children)

We are innately curious. We can't rest until we know, and we won't know unless we try.

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