I have a number of spatial database, through which I have identified particular types of land-cover. The topographic layer [defining land-cover] is made up of multi-polygons and I am using a separate point layer in order to join a classification type to it. However, the areas portrayed in the topographic layer may be formed from several individual polygons, without a total perimeter outline to identify the area. Therefore, the classification point may sit in just one individual polygon of the overall area [see below].
Example. Image is of a park, which consists of over 20 individual polygons. The point that classifies the area as a park sits within one of the polygons and cannot be attached to the entire area.
I would like to be able to apply the point based classification to the whole park area. I have tried to use ST_UNION function in order to do such, but have been unable. Does anyone know of a way to dissolve the area into a single shape/remove the pathways? This is a small example of a much larger data set, where there is little scope of manually defining area sand buffers in order to classify the data, thus I wondered if there was a practicable solution.
If anyone can help, it would be hugely appreciated....
SELECT ST_Collect(t.the_geom) as singlegeom FROM TABLE t; http://postgis.net/docs/ST_Collect.html
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I've got a few shape-layers with some polygons which all join up. I want to create a new shape which is the the hole in the middle of the other layers.
I've tried 'snapping', but it seems to lock to vertex and requires a lot of manual accuracy. Ideally i'd like to select the lines where they join and then 'fill in' the area. Though I don't know how to do this in QGIS.
You could use an algorithmic approach like the following (it assumes a situation as the one in the question, so no other holes and polygons are from different layers):
Merge vector layers to combine your different layers into one layer
Dissolve to combine all your features into one feature with one hole
Delete holes to get a layer with hole in the middle filled
Symmetrical Difference of output of 3. and 2. to get a layer where overlapping areas are removed i.e. only the hole should remain as a new layer
I'm trying to create an experience where I have a couple of detailed 3D models of buildings on the map with extruded building footprints of neighboring buildings via a vector tile source. The 3D models would be the main focus point and the extruded footprints would be for reference. One challenge I'm running into is that I have a global building footprint layer and it has a footprint for the 3D buildings which doesn't match up perfectly. Additionally, when extruded, it ends up merging/overlapping the nice 3D models.
I'd like to be able to hide the individual footprints that overlap the 3D models. My original thought was to grab the bounding box of the 3D model and then use the new within style expression, but it looks like this will only filter points and lines, not polygons. The building footprint polygons have no unique information in them that I could use to filter on.
I know I could monitor map movements and query the rendered features and manually detect intersecting polygons, but since there is no unique property on the footprint, I can't filter or use feature state.
Any ideas of how to efficiently avoid rendering individual polygons in a specific area that come in from a vector tile source?
It is a common issue that the buildings layer in Mapbox Streets don't contain any unique attributes to allow filtering or rendering differently.
The best solution is usually to source a different buildings layer, and in this case, remove those redundant buildings in pre-processing.
I can think of one rather crazy workaround that might work here, although the performance may be poor.
Add the building layer with very low opacity, of type fill, essentially invisible. (Maybe invisible would work.) Call your main source buildings`.
Create a secondary building source of type geojson, and a secondary fill-extrusion layer. Call this source buildings-copy.
On map move or moveend, use querySourceFeatures to obtain a copy of all buildings.
Process this copy using Turf to remove the buildings you don't want, and call setData to set the copy as the data for buildings-copy.
You may need to do some clever caching to get reasonable performance.
I've created a base layer and 6 different overlay (Points of Interest) layers for a leaflet map.
The base layer of markers can appear on the map almost anywhere in the world, but I want the POI layers to appear only if they are in the same area (mapBounds) of the base layer. Probably the screen size.
All the data is pulled from a MySQL database and using Ajax I create the various sets of markers from two different tables, base and poi. This much is all done and working, you can see it at https://net-control.us/map2.php. The green and blue markers are from the base table, other markers are currently selected for view by clicking on the appropriate icon in the lower right. The only one active at the moment is 'Fire Station'. But if you zoom out far enough you will see additional fire stations in the Kansas City area, and in Florida. Those sets are not needed.
After the query runs I create a fitBounds variable of the base layer and another poiBounds for the poi layer. But I'm not sure I need the poiBounds. The number of base markers is generally less than 50 for the base query, but if all the poi markers are pulled world wide that number could be very large.
So I'm hoping someone can help me determine a best practice for this kind of scenario and maybe offer up an example of how it should be done. Should I...
1) Download all POIs and not worry about them appearing outside the base bounds layer? Should I inhibit them from showing in the javascript or in the SQL? How?
2) If I inhibit the unwanted points from SQL do I test one POI at a time to see if its included in the base bounds? How? Are there MySQL functions perhaps to work with this kind of data?
I'm fairly new at leaflet maps and would appreciate examples if appropriate.
2) If I inhibit the unwanted points from SQL do I test one POI at a time to see if its included in the base bounds? How? Are there MySQL functions perhaps to work with this kind of data?
You probably want a column of type POINT, a spatial index on such column (which internally is likely to be implemented as an R-Tree), and spatial relation functions on your SQL query to make use of that index.
Start by reading https://dev.mysql.com/doc/refman/8.0/en/spatial-types.html. Take your time, as spatial databases, spatial data types and spatial indices work a bit differently than their non-spatial equivalents.
I'm fairly new to Leaflet library and I would like to ask if following functionality is somehow already implemented in Leaflet(or maybe in some other library).
I've found the following example which does clustering based on markers on the map and map also contains choropleth areas displayed.
My question is - Is it possible to do clustering based on choropleth data? Like if I have geojson data for some regions and would also have geojson data of subregions for every region. So if I do zooming then those subregions would collapse to big regions or big regions would be divided to small ones?
Big thanks for any advices or links!
No, because clustering algorithms work only on point data.
You might want to just hide the regions and display the "subregions" when zooming in.
If data becomes too dense when zooming out, consider making the union of the polygon geometries to display that instead. A naïve algorithm would be search for the smallest polygon, then search for the smallest neighboring polygon, replace them by their union, repeat. Stop the algorithm when the smallest polygon is larger than a given threshold.
I am dealing with storage of shapes. After a day spent to include the routines now I have some doubts.
The main trouble is recognize perfectly the new shape and know if already included or not.
I wrote something, and it works. I select all the shapes with same area and same number of vertex, and than I perform an Heuristic comparison. But, so just to be sure, I would ask you, if you know some direct algorithms, such matrix, spectrum, G theorm that gave two set of point can understand if the two sets are the same shape?
Before somebody screams about gis, the shapes can contain negatives shapes, better known with the name of holes. That are not to analyze in own coordinate system but in owner shape coord sys, where is the hole inside the other shape and his orientation. As far as I know, can gis nest shapes in other shapes and recognize them as whole shape.
Second place, what is the best way to store shape? I was thinking to store as array but I find it uncomfortable.