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Rotate, Scale, Translate in OpenLayers 4 and MapServer

Geographic Information Systems Asked by mapoholic on March 10, 2021

Sometimes, I get spatial data (usually DGNs but I am not sure the format matters) that in the coordinate control sheet a ‘Project Datum Factor’ is noted. Say: 1.000073496. If I add them as is in ArcMap, the features won’t align with the rest of my data. So in order to align them correctly, I use the "Rotate, Scale, Translate" option in the Transformation tab from the layer properties dialog where I enter the quotient of 1 divided by the Project Datum Factor. In this example 0.9999265094094 as shown below:

enter image description here

After doing that, all the layers line up perfectly.

My question is- is there an equivalent workflow I can use in an OpenLayers/MapServer only environment? Not even sure at what stage or level I should try to apply the transformation. The layers are rendered in the OpenLayers map as WMS and/or WFS layers using MapServer. So could MapServer -somehow- apply the transformation and send the tranformed image or vector data to the OL map? Can OL -again somehow- apply this kind of transformation?

One Answer

Your data is not in the EPSG:3089 coordinate system.

If you tell your software the actual coordinate system, then it is possible to convert the values into EPSG:3089 (or whatever you want to use).

EPSG:3089 uses a Lambert Conformal Conic projection; in MapServer, it could be described with these parameters:

PROJECTION
    "proj=lcc"
    "lat_1=37.0833333333333333"
    "lat_2=38.6666666666666667"
    "lat_0=36.3333333333333333"
    "lon_0=-85.75"
    "x_0=1500000"
    "y_0=1000000"
    "ellps=GRS80"
    "towgs84=0,0,0,0,0,0,0"
    "units=us-ft"
    "no_defs"
END

So in the layer definition, add this parameter (or maybe the reciprocal value) to correctly describe the custom coordinate system:

    "k_0=1.000073496"

(For the map and the other layers, you can use the init=epsg:3089 short form.)

Answered by CL. on March 10, 2021

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