CAD to GIS Workflow - TO BE UPDATED¶
GIS to CAD Workflow - TO BE UPDATED¶
Documentation - Tags retained after re-import of same geometry¶
Documentation - Tags retained after re-import of same geometry
The linework for infrastructure survey carried out by Eric Chacra in May 2020 was originally imported with a problem of ambiguity in the "Accuracy" table and in the "Accuracy" table.
The result was that lines did not inherit the attributes survey date, accuracy, equipment, surveyor.
Nevertheless lines were displayed on the Gisaf map, without these attributes, and tags were given to some of these lines.
The values for the two tables ("Accuracy", "Accuracy") have been corrected, ambiguity resolved.
The lines in the layers V-ELEC-UGND------E and V-COMM-CABL------E have been then reimported, the attributes have been properly assigned, and the tags have been retained.
4 August 2020
Access to data¶
Connection to server directly from CSR¶
To connect to the server directly without going through Aurinoco server, the correct url is
Connection to Gisaf via QGis through WFS / OGC API¶
This works only on QGis from version 3.14.15 onward
In the browser, click on WFS/OGC API, then right-click to create a new connection
Give a name (e.g. OGC API Qgis Gisaf)
Give the url https://gis.auroville.org.in/ogcapi
Under the WFS Options box, on Version dropdown, the default option "Maximum" works just fine
Click on OK
The list of layers will appear in the Browser under WFS/OGC API.
How to create a new projection in QGis¶
To create a new projection in QGis, go to menu "Settings", and click on "Custom Projections".
A pop-up window appears with a list of all projections defined in QGis projects used by the user so far.
Click on the green "+" sign on the right top part of the window to create a new projection.
In the "Name" box, type "TM CSRAUSPOS SF1" (which means TM = Transverse Mercator projection; CSRAUSPOS = theparameters for this projection are derived from the processing of DGPS raw data by AUSPOS - Online GPS Processing Service - https://www.ga.gov.au/scientific-topics/positioning-navigation/geodesy/auspos; SF1 = Scale Factor is 1).
In the "Format" dropdown list, select "Proj String (legacy - Not Recommended)"
In the "Parameters" box, paste the following "+proj=tmerc +lat_0=12.01605433+lon_0=79.80998934 +k=1 +x_0=370455.630 +y_0=1328608.994 +ellps=WGS84+towgs84=0,0,0,0,0,0,0 +units=m +no_defs".
Finally, click on OK.
In a more explicit way, the parameters mean the following:
Map Projection: TransverseMercator (TM)
False Easting: 370455.6300
False Northing: 1328608.9940
Latitude of Origin: 12°00'57.79560" (DMS) 12.01605433 (DD)
Central Meridian: 79°48'35.96164" (DMS) 79.80998934 (DD)
Scale Factor: 1.00000000
Zone Width: 6.0°
Elimination of Duplicate points – General criteria¶
It might happen that the same physical feature (e.g. a tree, or a pole) is surveyed more than once: this can happen because there are many physical features in an area, and the survey needs more than one station. So, for example a tree is surveyed from a station, and gets a serial number on that date. When the station is then changed, it might happen that the same tree is resurveyed: another serial number is given, and possibly a different date, if the survey from the second station happened on a different day.
It is clear that the same tree is then represented with two different points, which means that two different trees exist: but only one tree really exist in the physical reality.
It is clear that one of the two points is redundant and needs to be removed. If this is noted by the surveyor directly in the field, then the issue is solved by the surveyor himself during processing time.
If instead, due to various reasons, it was not noted by the surveyor in the field, it will need to be cleaned after the processing, possibly by post-processing staff.
How to identify duplicate points?
The following criteria can be used:
1. The distance between the two points is less than 30 cm (trees are surveyed if their trunk diameter is at least about 20 cm, so in 30 cm cannot exist two of them)
2. The orig_id (serial number) of the points are not in series
3. The survey date is not the same
4. In case of trees, the species of trees is the same
5. 5. In case of trees, the tree type is not TDEF (because TDEF are mapped irrespective of their diameter, so they can actually have a small trunk, and two of them might exist in 30 cm), not OT (many TDEF species are surveyed as OT if not otherwise indicated by a botanist)
6. The context needs to be evaluated: if one tree is deleted in an area where many trees exist in a limited space, then loosing one in the map is not a big error. If instead one tree is deleted where there are very few trees, then it might be a big loss.
Linework for the Survey Area¶
1. Creation of Initial Linework in QGIS using Survey points import - (Ram, System 4)¶
Initial Linework in QGIS is started by surveyor with the knowledge from the Field. For this step, points are simply imported into the QGIS from the field text file (.csv or .txt). CRS needs to be TM-AUSPOS. The box of “First record has field names” shall not be ticked. In Point Coordinates, select the correct field for x, for y and for z (usually “field_2” for x, “field_3” for y and “field_4” for z). Points can be styled using the “Categorized” style in “Symbology”, using “Field_5” as value, or using a Rule-based symbology using the category (field 5) as filter.
Linework is created by connecting points having same description and belonging to the same physical feature. All line and polygon features are created as lines.
The Initial Linework for the Survey Area is also stored temporarily in
Note: The line shapefiles / Geopackages shall be in CRS: TM AUSPOS¶
2. Creation of final working drawing Shapefiles / Geopackages - (Selvarani, System 1)¶
Final working drawing Shapefiles / Geopackages are created from the Initial Linework of Survey Area.
As the Surveyor draws all features as lines (both for lines and polygons features), the following actions shall be done:
1. If features are lines:
• Export the shapefile / geopackage into the final working drawing folder (Final WD), in separate folders according to its type (e.g. BLDG, FENC, ROAD, etc).
The CRS for the export shall be EPSG:4326 - WGS 84¶
2. If features are polygons:
• Lines shall be converted into polygons:
to do it, first click on the layer to be converted to make it active (e.g. WD-CZ-01-F-LL84_V-BLDG-MHOL------E), then go to “Vector” Menu, click on Geometry Tools, click on Line to Polygons:
The new window for “Lines to Polygons” conversion will appear:
• Always cross check the input layer, to make sure that the input layer is the active one
• Save the output in a temporary layer
• The temporary layer will be listed in the list of layers, it shall be exported to the saving location as (eg . D: > Survey > GB-01 > Final WD > A-Shp)
The CRS for the export shall be EPSG:4326 - WGS 84¶
Once all the shapefiles / geopackages are exported in Final WD, for each of the newly exported layers the Topology Checker Tool shall be used.
Linework for the whole Survey Zone¶
1. Merging Shapefiles / Geopackages - (Selvarani, System 1)¶
A copy of the Zone Master shapefiles / geopackages are taken from System 4 and stored in Temp Folder on Desktop in System 1.
Master shapefiles / geopackages are merged with the Survey Area shapefiles / geopackages:
• To do it, go to “Vector” Menu, click on Geoprocessing Tools, then click on Union:
The new window for “Union” will appear:
• To make sure that the right geometry is generated by this process (“line” type, not “Multiline”, and similarly “Polygon” type, not “Multipolygon), we need to always keep the Master shapefile (e.g. Final-CZ-01-2021-02-05-LL84_V-BLDG-MHOL------E) as Input layer, and the Survey Area shapefile as Overlay Layer (e.g. WD-CZ-01-F-LL84_V-BLDG-MHOL------E).
• (The output can be saved to a file, as the CRS should already be EPSG4326 – WGS84.)
2. Storing Shapefiles / Geopackages - (Selvarani, System 1)¶
Save the merged shape file in the correct location in Final folder as (eg . D: > Survey > GB-01 > Final)
Date in the name of Final Shapefile / Geopackage needs to be updated.
Once the merging operation is completed, the copy of Master shapefile / geopackage is deleted from the Temp folder.
3. Topology check of merged shapefiles¶
The topology checker is applied again on the merged shapefiles / geopackages.
The “id_field” shall be removed from the attribute table.
4. Archive and replace the Master Shapefiles / Geopackages (Ram, System 4)¶
Archive the previous master shapefiles / geopackages on system 4, and copy the new merged shapefiles / geopackages in its place.
*Then delete the Merged Shapefile / Geopackage folder from System 1. *
5. Note about Shapefiles and Geopackages¶
All the above works are usually done using shapefile format, in QGIS latest version (3.16.3).
The Geopackage export is done in QGis versions older than 3.12 (e.g. 3.4, 3.6, 3.8, 3.10) so that the lines are not saved as “Multilines” but as “Lines”and polygons are not saved as “Multipolygons” but as “Polygons”. This is very important to be noted, as Gisaf database does not accept the Multipolygon and Multiline geometry types.
A different way to create "Polygons" is to use the command Vector -> Geometry Tools -> Multipart to Single Parts and apply it to the layer: from "Multipolygon" it will become "Polygon" (check in layer Properties).
As on 13 March 2021, Gisaf can accept Multipolygon layers, because the command "Multipart to Single parts" has been integrated into the importing command (see Redmine ticket #11691)
Creating 3D Shapefile/Geopackage¶
While creating a Shapefile/Geopackage, the File name/Database-table name, Geometry type and CRS have to be entered.
In order to create a 3D Shapefile/Geopackage, the additional dimensions "Z(+M values)"/ "Include Z dimension" has to be ticked: this way the 3D Shapefile/Geopackage is accepted by Gisaf without errors, otherwise the Shapefile/Geopackage can't be imported in Gisaf because the Z dimension is missing (the geometries in the database are all 3D).
Exporting from QGis (shapefiles and/or geopackages) to CAD dxf format¶
An algorithm has been created by Selvarani, to see the whole process click here: