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35 votes
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Why is ellipsoidal distance greater than cartesian distance?

Cartesian distance is as measured on a flat Earth. Ellipsoidal distance is as measured on a spherical shape (or ellipsoid). To understand why the latter is longer, draw a circle and then draw a ...
MappaGnosis's user avatar
  • 33.9k
16 votes

Creating square polygons of given length from single corner point in QGIS

There is "Vector geometry > Geometry by Expression" tool in Processing Toolbox. You should use in a projected coordinate system. Select "Polygon" as "Output geometry type&...
Kadir Şahbaz's user avatar
15 votes
Accepted

Why accurate area of all countries cannot be obtained using a single EPSG code, even if it corresponds to an equal-area projection?

What went wrong: EPSG:3395 is not equal area The CRS you use, EPSG:3395, is definitely not an equal area projection. It is a World Mercator projection that heavily distorts areas, see here, including ...
Babel's user avatar
  • 73.1k
12 votes
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Calculating semi-major and semi-minor axis length of an ellipse in QGIS

Processing Toolbox -> Vector geometry -> Oriented minimum bounding box tool may be another solution. This tool already generates the width and height of the bounding boxes. Half of both will ...
Noura's user avatar
  • 3,429
12 votes
Accepted

Creating square polygons of given length from single corner point in QGIS

Use geometry by expression to create a point at 315 degrees azimuth from your point with a distance of the hypotenuse of the square, then create a box around the two points: bounds(collect_geometries( ...
Bera's user avatar
  • 74.8k
11 votes
Accepted

Calculating length of each polygon side in PostGIS

See: https://stackoverflow.com/questions/7595635/how-to-convert-polygon-data-into-line-segments-using-postgis : SELECT st_length(ST_MakeLine(sp,ep)) FROM -- extract the endpoints for every 2-point ...
Bera's user avatar
  • 74.8k
11 votes
Accepted

Generating lines at the end of each measurement with plugin in QGIS

Coming close to what you want, simply using geometry generator, you can use this expression to create the lines from each point to the cursor position where you click: make_line ( $geometry, @...
Babel's user avatar
  • 73.1k
10 votes
Accepted

How does $area function calculate area in QGIS?

Function $area: Returns the area of the current feature. The area calculated by this function respects both the current project's ellipsoid setting and area unit settings. For example, if an ...
Gabriel De Luca's user avatar
10 votes

Why accurate area of all countries cannot be obtained using a single EPSG code, even if it corresponds to an equal-area projection?

In addition to the fact that EPSG:3395 is not an equal area projection (therefore inaccurate for area measures), as mentioned by @Babel, a precise measure of the area requires a good projection. ...
radouxju's user avatar
  • 49.8k
10 votes

Calculating polygon area in QGIS without adding new field

The identify tool does offer you this information. Click any feature, then expand the topmost dropdown menu. Here all basic geometric information is hidden, incl. the area and circumfence.
Erik's user avatar
  • 16.5k
10 votes

Calculating polygon area in QGIS without adding new field

Create a label with the expressin $area (I should have used round($area)):
Bera's user avatar
  • 74.8k
8 votes
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Calculating polygon area in QGIS without adding new field

I personally find the identify tool sometimes too clunky. Here another approach: To show the area for a polygon without using an additional field, you can just use a formula for a label with the $area ...
Bernd V.'s user avatar
  • 3,199
7 votes

Calculating semi-major and semi-minor axis length of an ellipse in QGIS

Use Menu Processing / Toolbox / Minimum bounding geometry / Minimum Oriented Rectangle. Than the values you look for correspond to half of the sited of the rectangle. Edit: as described in @Kübras ...
Babel's user avatar
  • 73.1k
7 votes

Сreating buffer in meters using GeoPandas

Yes you need to reproject into a coordinate system with meters as units. import geopandas as gpd df = gpd.read_file(r'C:\GIS\data\tempdata\points_wgs84.shp') df = df.to_crs(3043) #Pick another df['...
Bera's user avatar
  • 74.8k
6 votes

Measuring distance between points in QGIS

Another option from mentioned by @Spacedman is the following: Connect target points with the source point (observation one) Measure distances for created lines This option could also help you to ...
Mykola Kozyr's user avatar
6 votes
Accepted

Measuring between points in QGIS

I don't think there is a plugin for that. But with a little sql, you can calculate it. If predecessor is defined by their id, then you can execute following code in the databasemanager: select a. ...
PieterB's user avatar
  • 5,287
6 votes

QGIS under measuring distances

That is happening because: You are drawing planimetric lines in a Mercator projection far away from its true scale curve (the equator in EPSG:3857); And the Mercator projection produces ...
Gabriel De Luca's user avatar
6 votes

Finding length and width of regular/irregular polygons in QGIS

You can use the Field calculator to find the with and length of the equivalent rectangle solving quadratic equation: Perimeter = 2 (a + b) Area = a * b => a = Area / b Substitute a into the first ...
Zoltan's user avatar
  • 7,400
6 votes
Accepted

Measure distance in km of polyline in QGIS

Create a new field with field calculator and this expression $length/1000. This was the short answer. More details in what follows, as things are a bit more complicated. How to calculate length? Use ...
Babel's user avatar
  • 73.1k
6 votes

Finding mean distance between cluster center and points in cluster in QGIS

On the layer with the center point, you can use QGIS expressions. Get an array of the points from the same cluster using array_foreach and then for each of these points create create a line to the ...
Babel's user avatar
  • 73.1k
6 votes

Generating lines at the end of each measurement with plugin in QGIS

You would probably need to create a custom map tool. For starters read about using the map canvas and creating map tools at the PyQGIS developer cookbook at https://docs.qgis.org/3.28/en/docs/...
til_b's user avatar
  • 5,144
5 votes
Accepted

Calculating distance between multiple associated points in QGIS

It's possible to do that from your XY coordinates. First you should create a table join between your list A to list B (this way because of 1 farmer per farmstead. it's a left join). Then create a new ...
Hugo Roussaffa's user avatar
5 votes

Measuring distance between points in QGIS

Put your observation point in a point layer and use "Distance Matrix" from the Vector... Analysis Tools menu. Make sure there's a unique ID column in your layer of points. I've got one point in the "...
Spacedman's user avatar
  • 65k
5 votes
Accepted

PostGIS Geometric V Geography measurements when using ST_Length

EPSG:3857 is also known as Web Mercator. Usual Mercator projections preserve angles but creates important distortions of size. Web Mercator has slight distortion of angles. Web Mercator shares some ...
thibautg's user avatar
  • 2,097
5 votes

How to calculate the mean distance between co-ordinates in QGIS

To find statistics on the nearest neighbors, you would go to Vector > Analysis tools > Nearest Neighbor Analysis. Upon completion, it displays a window that includes the mean distance. Make sure ...
JGH's user avatar
  • 42.3k
5 votes

Measuring distance between points along line in QGIS

I first thought this question was basically same as another recent question Points layer distance from the start of line layer in QGIS. However, there is an added complexity in this one, that OP ...
Kazuhito's user avatar
  • 31k
5 votes
Accepted

Deactivate Snapping for Measure Maptool (mActionMeasure) in QGIS temporarily

We could create a function whereby: If the mActionMeasure button is checked, the snapping mode is turned Off If the mActionMeasure button is unchecked, the snapping mode is turned On Here is the ...
Joseph's user avatar
  • 76k
5 votes

Finding length and width of regular/irregular polygons in QGIS

Try Minimum bounding geometry: Height and width attributes in output. You can join them back to the original data using id column.
Bera's user avatar
  • 74.8k
5 votes

Automatically updating feature area in the attribute table using QGIS

Let's assume there was created a feature and calculated an "area" attribute for it For catching changes done to that feature i.e. automatically updating the area, please set up some ...
Taras's user avatar
  • 33.3k
5 votes

Grouping and measuring total length of road based on specific attribute in QGIS

To get the km of cycleway for each type of highway, use this expression: sum("lunghezza", group_by:="highway") To get the percentage of each highway type, use this expression: sum(...
Babel's user avatar
  • 73.1k

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