Darren Cope
  • Member for 11 years, 3 months
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Teaching GIS, what to do and what not to do?
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17 votes

This question has been converted to Community Wiki and wiki locked because it is an example of a question that seeks a list of answers and appears to be popular enough to protect it from closure. ...

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Split Lines at Intersection of Other Lines
13 votes

Note that as of QGIS 2.8, there's a new tool in Processing Toolbox called "Split lines with lines" that does exactly this task and works beautifully.

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Creating polygon with extents of raster file in QGIS
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13 votes

Your question isn't clear. Do you want the 'rectangular' extents of the raster, or the extent of the features in the raster? For the rectangular extent, just use the "Tile Index" under Raster > ...

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How should I use GDAL to perform a transformation?
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12 votes

Actually, you will want gdalwarp, not gdaltransform. There are lots of examples out there. For example, gdalwarp -t_srs 'EPSG:4326' input.tif output.tif

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GDAL polygonize only certain raster values
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12 votes

No, it's not possible directly in the function. You can either a) reclassify the raster first (probably fastest and easiest), or 2) convert to vector then delete all non-zero polygons, or 3) create a ...

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How does manual Label Placement in QGIS 1.9 work?
12 votes

I've spent a bit more time with this, and think I have it more-or-less figured out. Here's what the new tools do, to the best of my knowledge (for those with more expertise, please feel free to ...

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Is there any tool/plugin for QGIS to easily select feature and edit attributes
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12 votes

The "Identify" tool will let you do this. There's a setting under Settings > Options > Map Tools tab > Open Feature Form, if a single feature is identified. Then just make sure your layer is editable, ...

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How to determine if an object is a circle
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10 votes

I would calculate the thinness ratio, which for a perfect circle will equal 1.0. The formula for thinness ratio is: T = 4pi(A/(P*P))

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Creating drive time polygons using Open Source tools?
10 votes

GRASS' v.net.iso can be used to to create the drive time 'network' which you could pass into a 'convex hull' command to get a polygon. Perhaps not ideal, but would work!

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Performing statistics or simple pie chart in QGIS?
9 votes

Giovanni is right. I outline the process here: http://darrencope.com/2011/11/01/qgis-diagrams-pie-charts-for-symbols/ To create a diagram symbol, go to the properties for the layer in question, and ...

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How to union polygons with common ID in QGIS?
9 votes

Do a dissolve on the ID field.

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Extract one GPS fix per day from data?
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8 votes

You should be able to do a simple 'select by expression' where DATECOLUMN like "% 12%" This is assuming your date is a string column. Essentially; the query is using the 'pattern' that is formed,...

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Join attributes of point and line layer by location (closest distance) in QGIS
8 votes

I don't think there's a 'core' QGIS function for this. However, install the MMQGIS plugin, and use the 'hub distance' tool. Chose your points as the "Source Points" layer, and your lines as the "...

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Creating space at intersection of two links
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8 votes

I would create intersection points, then buffer them by the distance of 'space' you want. Intersect the buffer with the lines, and delete those that intersect. Done.

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Clipping very large polygon datasets in ArcGIS?
8 votes

Or, you could give up on ArcGIS and try doing the clip in OGR. See an explanation here. I've found this works when nothing else does!

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Simplifying Shapefile using ArcGIS Desktop or alternative?
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8 votes

For a non-ArcGIS method, you could try QGIS - the "Simplify Geometries" tool under the Vector menu should do what you want!

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GRASS - Will r.to.vect work on this scanned map?
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8 votes

Tough one Chad. I suspect not as a first guess. The contours are quite 'light' and the graticule lines are very thick/heavy. You will likely end up with a poor set of results. However, I can run a ...

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Seeking Canadian postal code geometries
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7 votes

The Postal Code FSA Conversion files will be freely available as of Oct 24, 2012 as per the new data freedom initiative. See Census geography page of Statistics Canada for details. A list of all ...

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How to edit a group of selected features in QGIS?
7 votes

Matt: if the features have common attributes, you can theme them on those attributes. Check Properties > Style and choose Categorized or Rule-based and play around with the settings there.

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How can I get my GPS track data into a graphics program?
7 votes

GPS Babel is the tool you want. It can convert between a huge number of formats!

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Avoiding purple anomaly on imagery in ArcMap?
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7 votes

I would certainly go back to the original image and try rebuilding the pyramids. The fact that it disappears when zooming in to me means it's a pyramid issue. If it persists in ArcMap, do as @scw ...

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Slope analysis from NED data gives crazy histogram?
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6 votes

Interesting. I just did the same thing, with the same results. It turns out that QGIS assumes that the vertical units are the same as the CRS units. My test image was unprojected Lat/Lon and I'm ...

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How to create lines between pairs of two coordinates?
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6 votes

I just did something similar. I ended up stringing the from/to columns together in WKT format, and saving the file as a .txt which I then imported with the delimited text tool in QGIS. Select the WKT ...

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Permanently reordering fields in data (shp, gdb) without using FME or another ETL tool
6 votes

The QGIS "Table Manager" Plugin now also has the ability to perform this task easily with no command line necessary.

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Dealing with data that spreads across UTM Zones?
6 votes

Pick the UTM that most of your data falls in, and use it for all data. UTM Zones have (a half degree I believe of) overlap for just this reason. Measurements won't be too far off in this overlap ...

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Viewing LIDAR data (.las) in QGIS?
5 votes

GRASS has a documentation section on LiDAR in their wiki. Give it a read; you can use libLAS to import LiDAR data into GRASS, and then use many of the GRASS tools once it's in there.

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"add feature" tool QGIS 2.0 - polygon fill blocks view of what I want to digitize
5 votes

Under Settings > Options > Digitizing, Find the "Rubberband" setting, Then "Line Colour" and adjust the "Alpha Channel" on the colour chooser. I find that an Alpha value of 50 gives a nice level of ...

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QGIS, Table Manager cannot rename column title
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5 votes

If the column is the result of a join (as mentioned in your comment above) you'll have to save the shapefile to a new file (right-click in layer legend and Save As), then add it back to the map before ...

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v.dissolve to multipolygon
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5 votes

It looks like GRASS does in fact treat the result as a multipolygon, although QGIS displays it as separate features. I determined this by calculating the area on the feature(s) and they all came out ...

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Buffering with physical barrier using ArcGIS Desktop?
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5 votes

If I understand the question correctly, I would perform the buffer as normal, then intersect your buffer result with your physical barrier features (rivers?). Then do a select by location to select ...

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