[GIS] Contour lines (*.shp) into XYZ

elevationqgisxyz

I downloaded a TIFF image from USGS Earth Explorer from which I determined the contour lines and saved them in a shapefile (see tutorial http://www.qgistutorials.com/en/docs/working_with_terrain.html).

I would like to convert these features to points (just as this ArcGIS tool http://pro.arcgis.com/en/pro-app/tool-reference/data-management/feature-to-point.htm).

Each point should contain xyz information (simple CSV file or similar) which I can import as a surface elevation into FEFLOW (groundwater modelling)

I tried with MMQGIS which gives me the following output:

"shapeid","x","y" "1","-7.4266662066","37.1800028654" "1","-7.42583287327","37.1800083477" "1","-7.42582462244","37.1800000968" "2","-7.42583287327","37.1799959509" "3","-7.4266662066","37.1799959509" "3","-7.42749953994","37.1797223191" "3","-7.42833287327","37.1795834302" "3","-7.4291662066","37.1797917635" "4","-7.42999953994","37.1797223191" "4","-7.43083287327","37.1799959509" "4","-7.43083701921","37.1800000968" "4","-7.4316662066","37.1805556524" "4","-7.43208287327","37.1808334302"

What I want however is:

"x","y","z" "Latitude","Longitude","Elevation"

Best Answer

In two steps:

Extract nodes. Vector | Geometry Tools | Extract nodes (or from Processing Toolbox QGIS geoalgorithms | Vector geometry tools | Extract nodes
Save As... the produced Nodes layer as csv file. By default, the Geometry type would be Automatic . Make sure the Layer Options is set to GEOMETRY= AS_XY. (So, basically, leave it as is).

NB the extracted nodes can create a big file. Please consider decimating it before saving it to csv.

Related Solutions

[GIS] Labeling contour lines in ArcMap

Labeling using the Contour Placement style

Required: ArcMap

Clean (good) Data

Maplex Labeling Enabled. (see http://resources.arcgis.com/en/help/main/10.1/index.html#/A_quick_tour_of_the_Labeling_toolbar/00s800000014000000/)

The Maplex Label Engine groups the segments of contour features, if the symbology and label match and the features are connected, and treats them as single, long features

enter image description here

Official Documentation on Contour Label Placement

http://resources.arcgis.com/en/help/main/10.1/index.html#//00s800000064000000

[GIS] Creating sloped lines from XYZ in QGIS

if you are familar with scripting, you can use a python script to create 3D features. Inside the following example i assume to have a layer loaded inside qgis containing line string features and two fields named "from" and "to" which store the elevetion values for the first and the last vertice.

layer = iface.activeLayer()
iter = layer.getFeatures()
for feature in iter:
    # retrieve every feature with its geometry and attributes
    # fetch geometry
    geom = feature.geometry()
    # assume z values are stored in fields "from" and "to"
    p0z = feature["from"]
    p1z = feature["to"]

    # access Points, assuming each line has to vertices
    oldp0, oldp1 = geom.asPolyline()[0], geom.asPolyline()[1]

    # creating a new LineString with PointZ-vertices
    newp0 = QgsPointV2( QgsWKBTypes.PointZ, oldp0[0], oldp0[1], p0z )
    newp1 = QgsPointV2( QgsWKBTypes.PointZ, oldp1[0], oldp1[1], p1z )
    linez = QgsLineStringV2()
    linez.setPoints([newp0, newp1])
    # output
    print linez.asWkt()

this is just quick and dirty and you'll want to add code to store the new geometry into a new layer, but i left that out. The pyqgis developer cookbook describes, how to do that (http://docs.qgis.org/2.14/en/docs/pyqgis_developer_cookbook/vector.html).

As discussed in the comments, the data is stored inside a postgis database, so i can give a solution using SQL. I assume to have a table called linxyz with a geometry column "geom" along with "from" and "to" as z-values for the first/last point of a linestring geometry.

First add a second geometry column, it should have the same SRS as the original one (for me its SRID 4326 aka WGS84):

SELECT AddGeometryColumn ('linxyz','geomz', 4326, 'LINESTRING', 3);

Then use update to fill this new geometry column with a 3D linestring:

update linxyz set geomz = 
  ST_GeomFromText('LINESTRING(' ||
    ST_X(ST_StartPoint(geom)) || ' ' || 
    ST_Y(ST_StartPoint(geom)) || ' ' || "from" || ',' || 
    St_X(St_EndPoint(geom)) || ' ' ||
    St_Y(St_EndPoint(geom)) || ' ' || "to" ||
    ')' , 4326)

I used sql's string contatening operator || here to "build" the geometry from a WKT-String. Checking the result with select, shows the z-Dimension is present in the new column "geomz"

select ST_AsText(geomz) from linxyz

I'm not sure if this is the simplest way to accomplish this task, but it works in my little example :-)

Best Answer

Related Solutions

[GIS] Labeling contour lines in ArcMap

[GIS] Creating sloped lines from XYZ in QGIS

Related Question