Draft: fix import scale for Legacy DXF importer

Fixes #10253.

src/Mod/Draft/importDXF.py

@@ -706,7 +706,7 @@ def vec(pt):
     Base::Vector3 or float
         Each of the components of the vector, or the single numerical value,
         is rounded to the precision defined by `prec`,
-        and scaled by the amount of the global variable `dxfScaling`.
+        and scaled by the amount of the global variable `resolvedScale`.
 
     To do
     -----
@@ -714,14 +714,14 @@ def vec(pt):
     """
     if isinstance(pt, (int, float)):
         v = round(pt, prec())
-        if dxfScaling != 1:
-            v = v * dxfScaling
+        if resolvedScale != 1:
+            v = v * resolvedScale
     else:
         v = Vector(round(pt[0], prec()),
                    round(pt[1], prec()),
                    round(pt[2], prec()))
-        if dxfScaling != 1:
-            v.multiply(dxfScaling)
+        if resolvedScale != 1:
+            v.multiply(resolvedScale)
     return v
 
 
@@ -2076,6 +2076,90 @@ def addToBlock(obj, layer):
         layerBlocks[layer] = [obj]
 
 
+def getScaleFromDXF(header):
+    """Get the scale from the header of a drawing object.
+
+    Parameters
+    ----------
+    header : header object
+    """
+    data = header.data
+    if [9, "$INSUNITS"] in data:
+        insunits = data[data.index([9, "$INSUNITS"]) + 1][1]
+    elif [9, "$MEASUREMENT"] in data:
+        measurement = data[data.index([9, "$MEASUREMENT"]) + 1][1]
+        insunits = 1 if measurement == 0 else 4
+    else:
+        insunits = 0
+    match insunits:
+        case 0:
+            # Unspecified
+            return 1.0
+        case 1:
+            # Inches
+            return 25.4
+        case 2:
+            # Feet
+            return 25.4 * 12
+        case 3:
+            # Miles
+            return 1609344.0
+        case 4:
+            # Millimeters
+            return 1.0
+        case 5:
+            # Centimeters
+            return 10.0
+        case 6:
+            # Meters
+            return 1000.0
+        case 7:
+            # Kilometers
+            return 1000000.0
+        case 8:
+            # Microinches
+            return 25.4 / 1000.0
+        case 9:
+            # Mils
+            return 25.4 / 1000.0
+        case 10:
+            # Yards
+            return 3 * 12 * 25.4
+        case 11:
+            # Angstroms
+            return 0.0000001
+        case 12:
+            # Nanometers
+            return 0.000001
+        case 13:
+            # Microns
+            return 0.001
+        case 14:
+            # Decimeters
+            return 100.0
+        case 15:
+            # Decameters
+            return 10000.0
+        case 16:
+            # Hectometers
+            return 100000.0
+        case 17:
+            # Gigameters
+            return 1000000000000.0
+        case 18:
+            # AstronomicalUnits
+            return 149597870690000.0
+        case 19:
+            # LightYears
+            return 9454254955500000000.0
+        case 20:
+            # Parsecs
+            return 30856774879000000000.0
+        case _:
+            # Unsupported
+            return 1.0
+
+
 def processdxf(document, filename, getShapes=False, reComputeFlag=True):
     """Process the DXF file, creating Part objects in the document.
 
@@ -2137,6 +2221,8 @@ def processdxf(document, filename, getShapes=False, reComputeFlag=True):
         readPreferences()
     FCC.PrintMessage("opening " + filename + "...\n")
     drawing = dxfReader.readDXF(filename)
+    global resolvedScale
+    resolvedScale = getScaleFromDXF(drawing.header) * dxfScaling
     global layers
     layers = []
     global doc