Georeferencing Images and Geocoding Locations in AutoCAD

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What is georeferencing and geocoding?

 

When drawing maps, site plans, and other types of location-based content in AutoCAD, you probably encounter the terms georeferencing and geocoding. Georeferencing is building a relation between the internal coordinate system of a map, a scanned or aerial photo (e.g., those in your DWG), and a ground system of geographic coordinates (e.g., WGS 84 used for GPS). So, your DWG entities will get their geographic coordinates - latitude and longitude. Geocoding, or forward geocoding, is the process of converting addresses (e.g., street addresses) into geographic coordinates, which are then used to place points or symbols on a map. Reverse geocoding is the opposite process - converting point locations on a map to addresses (e.g., postal addresses, what3word codes, etc.).

 

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Geographic location for your DWG:

 

The first thing you will need for all these "geo" features is assigning the geographic location to your drawing. You can use the AutoCAD command GEOGRAPHICLOCATION (or similar tools in AutoCAD Map and Civil 3D) to insert geographic location information to your drawing file - by specifying the location of a reference point on a map provided by an online maps service and adjusting scale and offset. This process will assign a coordinate system (CS) to your DWG file. Many GIS coordinate systems are used in individual regions of the Earth, but AutoCAD supports all standard systems, so you can easily pick the one you need. If in doubt, use "WORLD-MERCATOR", the global WGS84. The selected coordinate system is stored in the variable CGEOCS.

 

Geo-tools you can use:

 

When you have a DWG "geolocated" (e.g., the coordinate system assigned), you can use the standard AutoCAD tools or third-party tools to utilize existing mapping data. The most obvious thing is overlaying the Bing aerial or OpenStreet map under your DWG geometry, putting your designed building, site, or gas line into the context of its surroundings. You can place markers based on their geo-coordinates (e.g., latitude, longitude) or extract lat-lon information from picked points.

 

On the ARKANCE's community site - CADforum.cz - you can find several useful geo-tools developed in VisualLISP, and all of them are free. Some of these tools are also available on Autodesk Apps. GeoRefImg (from Autodesk Apps) is probably the most popular - this tool automatically georeferences. (e.g., puts in the right place, with the right scale and rotation, any raster image which has a "world" file.) For .tiff files, this world file has the extension .tfw, for .jpg files it is .jgw, for .png images it is .pgw, etc. So, if you attach images with such world files into your DWGs, GeoRefImg can help you place them precisely where they belong on your map. With the freeware utility Geo2GPS you can display GPS (WGS84) or UTM coordinates of any clicked point in a georeferenced drawing. You can also open the related map in Google Maps or in Street View.

 

 

The freeware tool GeoCode converts any street address to an X,Y coordinate in your DWG map and optionally places a label at this point. You can also use it for reverse geocoding, so picking a point will display the postal address of that point (if any). Google Map API services are used for these functions. And this tool can also convert what3words (W3W) codes instead of street addresses.

 

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And you can even open Google Earth 3D maps in AutoCAD - zoomed in directly to the neighborhood of your project. (See the GEarth utility: https://www.cadforum.cz/en/how-to-open-google-earth-directly-in-your-autocad-window-tip13512)

 

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And if you don't use AutoCAD, you can still use many of these mapping coordinates tools - in the online converter at https://www.cadforum.cz/en/gps.asp

1 Comment
CGBenner
Community Manager

Great work, Vladimir!