44
Every polygon has, at a minimum, four distinct "centers":
The barycenter of its vertices.
The barycenter of its edges.
Its barycenter as a polygon.
A GIS-specific "center" useful for labeling (usually calculated with undocumented proprietary methods).
(They may accidentally coincide in special cases, but for "generic" polygons they are distinct points.)
A ...
44
Yes, there is an analytical solution for this problem. The algorithm you are looking for is known in polygon generalisation as "smallest surrounding rectangle".
The algorithm you describe is fine but in order to solve the problems you have listed, you can use the fact that the orientation of the MAR is the same as the one of one of the edges of the point ...
40
To supplement @julien's great solution, here is a working implementation in R, which could serve as pseudocode to guide any GIS-specific implementation (or be applied directly in R, of course). Input is an array of point coordinates. Output (the value of mbr) is an array of the vertices of the minimum bounding rectangle (with the first one repeated to ...
28
Well, WebGL is promising but has few features now. You can have a look to the API and examples.
From what I know, it is supported by FF4 and Chrome 9. You will find more about browsers compatibility on their website.
Javascript libraries :
http://cesium.agi.com/ and demos
To explore (samples and tutorials) :
A quite realistic 3D map using webGL and ...
20
I'm a little late to the party but here is another suggestion: http://potree.org/
It's an open souce, WebGL based point cloud viewer I've been working on for quite a while.
== UPDATE ==
It can render large amounts of colored point clouds. LIDAR data without colors will be supported soon.
Showcase: http://potree.org/wp/demo/
Source code: https://github....
18
What makes GIS stand out from graphic design and cartography is its use of quantitative reasoning and scientific and engineering principles. Let's see how this can work without getting bogged down in unnecessary calculations.
Some Facts
In GIS it is indeed useful to have a good intuition for lengths, areas, and even volumes. I'll get to that, but let's ...
16
1) For a full 3D GIS, the better is GRASS GIS, look at Screenshots of 3D data management or From drone-aerial pictures to DEM and ORTHOPHOTO: the case of Caldonazzo's castle, from example.
Some examples (interactive: you can scale, rotate the representation and many other things) :
DEM with 3D points:
Draped raster on the DEM
Draped geological map with ...
15
To create cross section:
use ArcGIS, MapInfo, etc. with point XYZ data projected on either south-north or east-west plane
or use dedicated geological software to create the section (Geosoft Target, Leapfrog Mining, Rockworks, Datamine Studio, etc.) Might require some post-processing to manually add or adjust labels and text
To create 3D topo/subsurface ...
answered Mar 27 '12 at 17:18
Jakub Sisak GeoGraphics
15.2k19 gold badges83 silver badges164 bronze badges
14
ReadyMap might be another option. Here is an example (with a bonus of Leaflet integration!) [via @LeafletJS]:
And one more with 3D overlay on the globe:
More: demos, code.
Update: The project seems to change its course rather drastically. ReadyMap is now:
Free Data Service for ReadyMap and osgEarth Developers
And the 3D globe application moved (most ...
14
When there is no implicit cast between two datatypes you need to state it explicitly. In your case ST_Force_3D (or ST_Force3D for PostGIS 2.1 and later) should do the trick:
ALTER TABLE cl
ALTER COLUMN geom TYPE geometry(MultiLineStringZ)
USING ST_Force_3D(geom);
11
Not sure if standard GIS packages are going to give you what you need. You might have to get into 3D animation/visualization packages such as Vue (paid, but not too $$, maybe around $1,000 US) or Blender (open source with HUGE community). I'd love to know what the NPS used to create the flyover you referenced.
I'm currently struggling with getting real ...
11
I have created a couple of ArcGlobe videos in the past (~4yrs ago) that look to have about the same video quality as the NPS video you referenced. The key that I was told (and found to be true) was to:
use keyframes to allow the software to create the appropriate
transition between locations,
capture the video at 4x - 8x times SLOWER than you want to ...
11
This is not the first time I encounter such question and generally it is asked by people outside of geospatial industry that are not familiar with cartographic theory or with practice needs (this is just my observation).
As to the question:
A "3d Globe" that you see on the screen is nothing less than just an Azimutal projection... And there is no such ...
11
3D globes and the like are very useful for quick visualization purposes. You can instantly see Global Level and Continental Level data, and spatial relationships and distances are easily understood.
However if you think about it, you don't really need a Globe foe every such case. As SS_Rebelious has mentioned, a Globe on a Flat Screen, is basically an ...
11
Thank you for clarifying your question as it was previously quite unclear. You can read a multiband raster using the stack or brick function in the raster package and assign the associated RGB values to an sp SpatialPointsDataFrame object using extract, also from raster. Coercion of the data.frame object (which results from read.csv) to an sp point object,...
10
Yes, it is possible but using a Python script in the console
see For geologists: 3D geological boreholes
I presented the scripts in visualizing 3D data (Z values) or data with z attribute: a solution
or QGIS, représentation 3D des couches vectorielles (shapefiles dits 3D ou shapefiles avec attributs z) avec les modules Python Matplotlib ou Visvis à ...
10
It's super-easy in QGIS 3.0:
Run the "Set Z Value" Processing algorithm
Click the button on the right of "Z Value", and select Field -> "DYBDE".
Run the algorithm. The z values for the geometry's vertices will be set to the value from the DYBDE field.
In case you have the values of depths and you want to get elevation values with negative number for ...
9
The Describe object also has the hasM and hasZ properties.
8
To close a multipatch feature, it must completely enclose a volume. Multipatch features created with the Interpolate multipatch to polygon (using a surface) tool can likely not be closed. (Unless you extrude between 2 TIN surfaces which should produce a closed multipatch. Personally, I have not had a lot of success using "Extrude Between" with complex ...
answered Oct 3 '11 at 20:02
Jakub Sisak GeoGraphics
15.2k19 gold badges83 silver badges164 bronze badges
8
I just implemented this myself and posted my answer over on StackOverflow, but I figured I'd drop my version here for others to view:
import numpy as np
from scipy.spatial import ConvexHull
def minimum_bounding_rectangle(points):
"""
Find the smallest bounding rectangle for a set of points.
Returns a set of points representing the corners of ...
8
Write your data into a new shapefile with ogr2ogr and force geometry type into 2D with the -dim switch.
ogr2ogr -f "ESRI Shapefile" output_2d.shp input_zm.shp -dim 2
The -dim setting is not limited to shapefiles but works in the same way for most vector formats. One exception I know is Oracle Spatial that does not honour the ogr2ogr switch but you must ...
8
In QGIS v3.0 you can use directly QgsPoint:
zPoint = QgsPoint(-74, 4, 2600) # x, y, z
zPoint.z() # Prints 2600.0
Whereas in QGIS >= 2.10 you need to use QgsPointV2:
zPoint = QgsPointV2( QgsWKBTypes.PointZ, -74, 4, 2600 ) # type, x, y, z
zPoint.z() # Prints 2600.0
This is an example with a memory layer using QGIS 2.14 (based on the PyQGIS Cookbook):
...
7
You can render from POSTGIS with OSM data in 3D
http://wiki.openstreetmap.org/wiki/OSM-3D
NOTE:
"Preparing OSM data to be viewed in OSM-3D requires a lot of preprocessing steps which are done on GIScience's servers."
see the ZIMBA server
http://wiki.openstreetmap.org/wiki/OSM-3D#Servers
7
If you want to get a 3D DXF from a SHP (SHPfile generated from DTM with
Qgis-Processing-Tools-GDAL/OGR Extraction-Contour), you must:
1) have column with Z values into Table attributes of SHP.
2) open "OSGeo4W Shell Commands" if you have Windows OS.
3) write into shell for example:
ogr2ogr -f "dxf" d:\Temp\3Doutput.dxf d:\Temp\contour.shp -zfield ELEV
...
7
There is a paper called "Curved Reconstruction from Unorganized Points" by In-Kwon Lee which looks into constructing lines/curves from a set of points without any ordering by exploiting the moving least-squares method. Although it focues on 2D applications, it mentions the possibility of extending this to higher dimensions. The following image is taken from ...
7
I know QGIS has a plugin that export DEM to STL using DEMto3D, and I tested on a DEM and it worked. The description of the plugin mentioned that clearly:
DEMto3D is the first tool that links GIS (Geographic Information
System) and 3D printing. DEMto3D allows export DEM to STL format ready
to 3D printing.
Here is the homepage of the demto3d, and there ...
7
what you're talking about is an anaglyph map.
it's possible using standard QGIS symbology
here's an example I did a while back.
The buildings were given a size attribute (probably using $area)
The idea is for big buildings (by area) appear closer to the viewer, and smaller ones further away.
These polygons were given a rank (0=largest set, 1= next ...
6
There is a project at https://gitorious.org/osm2blender that imports Openstreetmap map xml data and renders in in 2.5d using the open source 3d suite Blender.
An online OpenLayers example of the output can be found at http://www.anzui.de/osm2blender/openlayers/
6
Natural Scene Designer is an excellent tool for fly throughs. It's affordable too. However, I'm not certain about flying underground. Although, if you have sketup pro you should be able to create something.
This methodology used to work with the free version of sketchup, but doesn't anymore, it should work with the pro version. To get your terrain data ...
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