41

The idea with hexagons is to reduce sampling bias from edge effects of the grid shape, which is related to high perimeter:area ratios. A circle is the lowest ratio, but cannot form a continuous grid, and hexagons are the closest shape to a circle that can still form a grid. Also, if you are working over a larger area, a square grid will suffer more from ...


27

One of the benefits, that I've seen when doing wildlife or habitat modelling especially, is that hexagons allow patterns in the data (ex, edge of a field or any other patch) to be seen more easily than what squares would of offered. Think of a soccer ball too, though not always hexagons, those geometric shapes fit to a curved surface quite nicely. In your ...


20

The hexagon is the most complex regular polygon that can fill a plane (without gaps or overlap). I can see two advantages: It is closer to a circle than the square in terms of shape, so you suffer less from orientation bias (lower anisotropy with hexagons) and it is more compact (lower shape index: perimeter²/area). It therefore provides more accurate ...


17

Actually it's not all that situation dependent and is all about statistical error. Any time you resample to a higher resolution, you are introducing false accuracy. Consider a set of data measured in feet at whole numbers only. Any given point may be +/- 0.5 feet from its actual location. If you resample to the nearest tenth, you are now saying any given ...


11

The link provided by @Mapperz mentioned that some of the potential sites "were considered at a MSL Project and MSL Landing Site Steering Committee meeting in Dec. 2009 that emphasized discussion of the science merit of the sites as well as landing site safety based on initial evaluation of thermal inertia, slopes, and other first order safety parameters." ...


10

The paper "Multiscale Analysis of Topographic Surface Roughness in the Midland Valley, Scotland" by Grohmann et al., 2011 describes the differences between a six methods of calculating surface roughness measurements from 2D digital topography. His paper was helpful since he provides a quantitative comparison of each method using a single test region at ...


10

I believe the AreaOnAreaOverlayer is the transformer that performs the equivalent of an ArcGIS Union. Performs an area-on-area overlay so that all input areas are intersected against each other and resultant area features are created and output. The resultant areas have all the attributes of all the original features in which they are contained. ...


10

Yesterday I had no time to create it in details... See my solution in 4 steps: CREATE OR REPLACE VIEW bd_segment AS SELECT ST_PointN(geom, generate_series(1, ST_NPoints(geom)-1)) AS sp, ST_PointN(geom, generate_series(2, ST_NPoints(geom) )) AS ep FROM -- extract the individual linestrings (SELECT (ST_Dump(ST_Boundary(the_geom))...


9

Slope analysis is performed on a DEM (raster layer with elevation values). This is one way to do it. If your contours have an elevation value, you can use the interpolation option (raster/interpolation) to produce a DEM. For instance, here are my contours as a shapefile The attribute table do have a value for altitudes in the "elevacion" field. Now you can ...


8

This question refers to the Getis-Ord GI* hot-spot analysis tool in ArcGIS. One can find an explanation of the tool here: http://webhelp.esri.com/ARCGISDESKTOP/9.3/index.cfm?TopicName=Hot_Spot_Analysis_(Getis-Ord_Gi*)_(Spatial_Statistics) The assumption that hot-spot is a synonym for heat-map is incorrect. Heat-map has a wide variety of definitions, whereas ...


8

This is known as swept-path analysis. It is one of those calculations that seems initially to be relatively trivial but soon becomes obvious that there is a lot more to it because it is not just the tightness of the turn that is important. Some of the other things to consider include: Length of the vehicle and point of articulation. Turning circle of the ...


7

I'm working on a windows machine, but you can: Select your cities with the selection tool (should be on the tool bar, or under View > select). Also, there needs to be a column with population data in the attributes, of course. Then create a buffer with your desired radius (Vector > Geoprocessing Tools > Buffer(s)). Make sure to "Use only selected features", ...


7

These activities should all be easily done in QGIS, point by point as per your question: Symbols can be given radii based on a field. In the Symbology properties tab, select 'advanced', 'size scale field' and then the field with the radius (the CRS of the project will need to be in metres). The score can be stored in an attribute field; "Join attributes by ...


7

This paper: Christophe & Ruas 2002, Detecting Building Alignments for Generalisation Purposes, ISPRS, Ottawa. describes an operational method for the detection of small surfaces (buildings) alignements - it should work even better with points! (this method is rather robust since it is used for the production of 1:25000 maps in France).


7

The following is a rough outline of what you might do. I won't include a great deal of detail, you can research further using these terms and/or ask new more specific questions. Note: you will need to careful of coordinate systems. Firstly that they are the same for your datasets, and second that they use metric (metres) horizontal units (not actually ...


7

Very interesting question! Found a couple more examples and included a brief quote and their citation (quite fun to see how GIS software can be used in completely nongeographical applications): LASER CONFOCAL MICROSCOPY AND GEOGRAPHIC INFORMATION SYSTEMS IN THE STUDY OF DENTAL MORPHOLOGY "...original specimens of Recent teeth can often be optically ...


7

The only geoprocessing tools you need for that is Intersect (Analysis toolbox) and Join Field (Data Management toolbox). Run Intersect on the land use and watershed polygons which will result in the intersection of those two layers (your watershed layer will be clipped to the borders of your land use layer while having all the attributes preserved). Then ...


6

For the described issue I don't see the point in actually using GIS (you didn't mention that you have to visualise data). This issue (especially if it is routine one) can be solved by several quite simple SQL-statements. Consider using PostGIS or Spatialite (depends on your data amount). I believe another alternative is to use OGR scripting but I would ...


6

Yes, use the xlrd library. See parsing excel documents with python question on Stack Overflow.


6

Though being late to this party (;-) I'd like to point to this prototype which probably answers this thread: QGIS plugin for hotspot analyis by Stanly Shaji et al..


6

The same way you calculate any mean from a set of numbers. The sum of the numbers divided by the count Mean x = (X1 + X2 + X3....XN)/N Mean Y = (Y1 + Y2 + Y3....YN)/N


6

There are a few ways to do this. I have completed this in the past with great results using a combination of attributes and raster processing. The premise of the process is to assign each feature with a value of n (1, 2, 4, 8, 16, 32, 64, etc.). Assigning these values ensures that when you subtract layer one (1985) from layer 2 (1997) you get a unique ...


6

You can use the intersect tool in the Vector menu under Geoprocessing Tools. You select the two layers you are interested and an output location. This will create a new shapefile with the attributes of the overlapping features. In the attributes you should then have the MPO and Congressional District numbers.


6

I'm the author of Past and that paper you refer to. From your plot it seems like you have used a too large search radius. Try to decrease the Radius value. Also, if you would like to detect more lines, increase the alpha value (significance level).


6

I would use Python's itertools and a SearchCursor for a very efficient way to find the spatial relationships you are after. You can incorporate the geometry methods overlaps, contains, and equal to get at the geometry properties. Start off by creating a function to better organize the workflow and for repeatability def findOverlaps(x): Open a search ...


5

I'm not aware of a ready-made function that does this, but you can use the Processing Modeller in QGIS to build such a function yourself. To do this, you can run the "Vector/Overlay/Intersection" and "Vectors/Overlay/Difference" tool, both using the contours layer as the "Input Layer" and the glacier layer as the "Intersect Layer". The outputs of those ...


5

A key disadvantage of grid squares is that the sample rate is substantially lower along the diagonal vectors to those of the four sides (Jasons point above). If you have some regular linear pattern to your data the orientation of the grid affects the effective sample rate of each context. For example if you have a series of ridges and valleys, orienting ...


5

You can use Data Driven Pages to quickly loop through each feature of your feature class. Within the settings you can set up what % you want to zoom to - i.e. 100% will have the feature fill the screen, but you might want to try something like 150%. This tool, although designed to make maps, is also useful for inspecting features quickly.


5

There are other applications in processing microscope images like the one from your example. A well known geospatial image processing software called eCognition was developed originally by Definiens - a company who does a lot of image processing in the medical and life science domain. See this older press release: http://www.definiens.com/about-definiens/...


4

there are lots of method for calculating land use change in gis systems. if you want to use Arcgis, you should check out Confusion Matrix Analysis for your work. with confusion matrix you can also measure urban sprawl, too.. it is of course necessary to do some research. Wikipedia defination: In the field of artificial intelligence, a confusion matrix is ...


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