cad gis wordleThe top two spatial data formats people are translating are Esri Shape and Bentley MicroStation Design, according to FME usage statistics from 2013. Autodesk AutoCAD DWG/DXF isn’t far behind.

What’s interesting is that these two formats naturally integrate about as well as orange juice and toothpaste. Esri Shapefiles hold GIS features and MicroStation DGN files hold CAD drawings – and the nature of GIS and CAD data types are so different that attempting to combine them can leave a pretty bad taste.

Despite this, translating between CAD and GIS formats is a common venture. In this post, we’ll explore the challenges and solutions with converting GIS to CAD. This is part 2 in a series about CAD-GIS integration. Read about moving data from CAD to GIS in part 1, and round-tripping data between CAD and GIS in part 3.

GIS and CAD basics

For a brief overview of CAD and GIS formats, check out this blog post on converting CAD to GIS.

SHP to DWG, GDB to DGN, and what it all comes down to

Whether your GIS data format is Esri Shapefile, Esri Geodatabase, Oracle Spatial, SQL Server, MapInfo, PostGIS, GML, or otherwise, your goal comes down to converting GIS features (i.e., data structures and attributes) into information-rich CAD drawings.

In a poll during our December 2013 webinar, we found that 39% of users have problems creating CAD symbology when exporting from GIS. Thankfully, with the help of a translation process that understands the properties of GIS features and CAD drawings, converting between these data types is easy.

The keys to successful GIS-CAD integration

Waffles and OJ

Orange juice and toothpaste might not go very well together, but you know what orange juice does go well with? Breakfast. So let’s put in a bit of effort and prepare some waffles with that GIS dataset.

A successful GIS to CAD translation must read from GIS, style the data, then write it out to CAD. In other words, it needs a robust spatial ETL process.

1. Rich data model

We need to convert GIS data structures into complex geometries used by CAD applications. This means using a rich data model that offers a lossless translation into equivalent structures in the output CAD dataset. For example, we might want to turn GIS point features into MicroStation cells or AutoCAD blocks.

Further, GIS attributes must be converted to CAD annotations and symbology. The data model should also be able to translate important information like tags, AutoCAD extended entity data, or Map3D object data.

2. Sophisticated data transformation

Converting GIS to CAD might involve a variety of specialized transformations to text, geometry, and other objects.

Converting GIS to CAD might involve a variety of specialized transformations to text, geometry, and other objects.

Just as important as the data representation is the ability to transform the data. In the middle of the E and the L of ETL, we need to define the content and style of the output CAD objects. For example, when translating from GIS point features to MicroStation cells, we can set the size of each cell based on the value of a field in the source GIS data.

Styling the drawing / design might involve a combination of setting colors, picking a template file, or configuring blocks, lines, areas, symbols, or text. It might involve transformations like converting lines into polygons, generating text labels, clipping data to a given boundary, or extruding 2D geometries into 3D solids.

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With a rich data model and sophisticated data transformation, you can integrate your GIS and CAD data without leaving a bad taste. Your output CAD file will contain all the required data to be able to be used by a CAD technician. So enjoy that orange juice – you earned it!

What obstacles have you dealt with in GIS-CAD translations? What other types of data translations would you like us to delve into in a future post?

FME tumbler with OJ

About Data ArcGIS AutoCAD Autodesk CAD Data Transformation Esri GIS Interoperability MicroStation Spatial Data Interoperability Transformation

Tiana Warner

Tiana is a product marketing manager at Safe Software. Her background in computer programming and creative hobbies led her to be one of the main producers of creative content for Safe Software. Tiana spends her free time writing fantasy novels and riding her horse, Bailey.

Comments

7 Responses to “GIS to CAD Conversion in Two Parts”

  1. Doug Osborne says:

    If the data resides in an open schematic database then the conversion between GIS and CADD tech becomes trivial. Each reads the database and portrays the data in the customary way.

    The real issue is the quality of the data. To move between the two worlds the actual spatial data can’t be at the old fashioned mapping standard but needs to be spatially accurate to an exacting tolerance. I prefer centimeter accuracy but will accept up to a foot spatial error depending on the feature.

    There has been too much emphasis on tools and not enough on the work. At this point, everyone has inclusive tool sets that read other types of data. The key is to ensure that data is worth reading.

  2. Tiana Warner says:

    Hi Doug,

    You raise an excellent point: quality assurance is a huge deal. If the data isn’t robust then why bother transforming it? Because of this, we spend a lot of time developing comprehensive data validation for FME. A key step in any translation should be to identify and solve issues in the datasets.

    Sincerely,
    Tiana Warner

  3. Bryan says:

    Tiana,

    Here are a couple questions I have about FME when translating to the DWG format:

    Scaling
    What is the best way to take an area defined by a bbox in say an EPSG 4326 coordinate system and map that into a DWG for printing at a certain scale, say 1″ = 400′ while also keeping everything “square” (distances equal)?

    Labels
    What’s a good way to generate CAD leader-lines and text boxes to indicate the textized attributes for various items?

    Templates
    Can we use templates and then insert attribute data into things like a drawing name, revision date, etc?

    Thanks,
    Bryan

  4. Alex Butor says:

    i have a polygon shapefile covering the whole area with its land cover. In addition, some landcover were clipped by buildings and other manmade structures (ex. Shelter) that gives holes. When i export it to CAD, the process creates polygons on that holes that makes conflict on the total number of features from the source layer to the output CAD layer. Any solution to this conversion? Thanks

  5. Alex Butor says:

    By the way im using ArcGIS 10 and exporting it to DXF CAD format.

    • Tiana Warner says:

      Hi Alex,

      Normal polygons written to ACAD become closed lines, so you’ll need to convert the polygons to MPolygon or Hatch to retain the outer shell / hole relationship.

      Hope that helps,

      Tiana

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