Handling Geospatial Coordinates for 3D PDF Files
A Practical Work-flow Guide for adding location information on DWG 3D Terrain models and draping geo-referenced images
Extending 3D PDF applications for 3D Geospatial data requires some additional steps and special treatment for geospatial coordinate data. This practical guide shows how to export a DWG terrain surface model from AutoCAD© Civil3D© as a simple non-geospatial surface mesh object, add a projected (geospatial) coordinate system to it, drape a georeferenced JPEG image overlay, and embed a geospatial-aware probe to support the 3D scene interaction. The built-in 3D measure tools in the Adobe Reader& Acrobat lack geospatial location reporting, so the work-flow outlined here adds additional information and tools to support geospatial 3D PDF content.
The universal PDF format is ideal for sharing information and collaborating with clients and remote team members. The built-in 3D features can be exploited for geospatial and civil engineering applications where review and measurement within a PDF document, avoiding the need to run GIS specific software. The technical details about geospatial coordinate systems, the way data is encoded, and the various geospatial projections are outside the scope of this article.
For the purposes of this work-flow example, multiple data files will be imported and combined:
- DWG Terrain Surface Model, as a classic ACAD model exported from Civil3D as an exploded set of triangles rather than as a native DTM. As such this export lacks geospatial coordinate context information.
- A Georeferenced image in JPEG format (JPG) with a world file (JPW) specifying position, scaling and rotational corrections for a projected coordinate system (PCS).
- Additional 3D geometry objects (vehicles, buildings, bridges, pipelines, wells…) can also be merged and positioned, as long as the local datum is known for translation (not shown in video).
Built-in Adobe Measurement
The default Reader includes a measurement tool for marking any two points on a model and adding mark-up to show the distance value in 3D model space. However, there is nothing available to simply probe to reveal the absolute position data at a given point, and often the distance is more useful as 2D map (horizontal) distance rather than as a “line of sight” distance.
Specifying Geospatial Projected Coordinate System to DWG
By using PDF3D ReportGen, on the “Geospatial” feature menus, any imported object (in this case the DWG terrain) can be assigned appropriate geospatial coordinate information. It can be specified as a geodetic Latitude and Longitude, typically in WGS84 conventions, or as a projected UTM “tile”, specified by name or often using the EPSG coding reference number. In advanced cases, a full well-known-text (WTK) information block can be specified. Once setup and exported in PDF, the geospatial coordinate system gets embedded and carried inside the PDF, so no other external software is required.
Adding On-Page Geo-location Probe
By using PDF3D ReportGen extended features, additional interactive controls can be inserted onto the PDF page. In this work-flow, a mouse “Probe” is added, so that selections in the 3D scene are marked with a small arrow, and the geospatial coordinate data (if available) are shown below the scene in a PDF page form line. The probe feature is implemented using PDF interactive form field features supported by ECMAScript.
Image Draping, Visual Appearance
In this work-flow the JPEG geo-referenced satellite image is draped onto the DWG terrain surface, by specifying it on the PDF3D ReportGen Geospatial menu section. The JPEG image has an accompanying JPW world-file to specify the projected coordinate data for this image. Normally 3D PDF is used for manufacturing, 3D parts, where surfaces may be shiny or lit to reveal 3D details. In this case, the JPEG image already contains most of the important information that needs to be viewed clearly, so the material properties are adjusted to emphasize the origin image pixel color values. The Diffuse, Specular and Ambient color is set to black, to zero-out their effects. The Emissive material factor is set to full 1.0 (white) so that the original JPEG image appears as clearly as possible on the 3D surface after draping.
3D PDF with Geo-Location
Enhanced 3D PDF Scene with Geo-Location Probe showing Latitude-Longitude or Projected UTM Zone Location is added into the PDF page by ReportGen. This feature enables direct mouse-click location readout, with interactive switching between Latitude-Longitude mode and the projected zone Eastings-Northings. The Left-Mouse selection can also be changed for distance, both in true 3D distance and projected map distance, 3-point angle measurements, and Grade or Slope in percent, angle and ratio forms, especially helpful in civil engineering projects. The coordinate readout also can be changed to MGRS (defense applications) and Earth-Centric projections (for polar regions).
For more information:
Geospatial data support overview https://www.pdf3d.com/geospatial/