Coordinate Systems & EPSG Setup
Scans, drawings and orthophotos from different people only line up if SkyGIS knows which coordinate system each one uses. You set the project CRS by EPSG code or work in local coordinates, give every upload its source CRS, and check placement at points you know before anyone measures or compares.
- Project CRS
- EPSG search, or local coordinates
- Placement fixes
- Layer offsets and rotations
- Vector export
- Project CRS or WGS84
Getting every layer into the same coordinate system
Collect the reference details
Ask each data provider for the CRS (ideally as an EPSG code), the units and the height datum they used.
Set the project CRS
Search for the EPSG code when you set up the project, or choose local coordinates if the site has no geographic reference.
Give each upload its source CRS
Set it on import. For DWG and DXF, check the drawing units as well.
Check against points you know
Read coordinates in the viewer at a control point, building corner or kerb, and compare them with the survey report or drawing.
Adjust and record
If one layer is still out, apply an offset or rotation to that layer and write down what you applied, so nobody mistakes it for the original placement.
Typical problem
The drawing that lands nowhere near the scan
The scan is in the national grid. The architect's DWG was drawn on a local site grid with its origin at a building corner. Both upload without errors, and the drawing appears a long way from the point cloud.
Choosing another EPSG code won't fix it, because the drawing isn't in any EPSG system. Either ask for the drawing in the project grid, or place it with an offset and rotation against features you can see in the scan, and record what you applied.
Project CRS, local coordinates or WGS84?
Projected CRS
The usual choice. Search the EPSG list and set it for the project. Stockpile volumes and LandXML imports expect a projected, metre-based system.
Local coordinates
For sites with no geographic reference, such as a building survey on an arbitrary grid. Every layer must share the same local system and units.
WGS84 on export
Vector exports can be written in the project CRS or in WGS84. Choose WGS84 when the recipient's software expects latitude and longitude.
Questions
Why does the coordinate system matter when data comes from different suppliers?
Scans, drawings and orthophotos from different people only line up if SkyGIS knows which coordinate system each one uses. Getting it right at upload is what lets you measure across layers and compare design with survey.
Why doesn't my DWG line up with the point cloud?
Usually the drawing was uploaded with the wrong coordinate system or units, or it was drawn on a local site grid. Ask the supplier for a version in the project grid, or place it with an offset and rotation for the review and record what you applied.
Can I work on a site with no geographic reference?
Yes. Create a project in local coordinates. Every layer in it then needs to use the same local system and units.
Does SkyGIS correct a badly registered scan?
No. The coordinate system tells SkyGIS how a file's coordinates are written; it doesn't fix the survey. Ask your supplier for registered, georeferenced data, because that work belongs in the scanning software before upload.
Check your layers line up
Set up a free project in your survey's coordinate system and upload a scan and a drawing. Read a few coordinates before you send anyone the link.