Maps with datum Hong Kong 1929

I have scans of some 50 years old maps that I need to rectify so as to compare them with modern maps of today. These maps are supposed to be using the Hong Kong 1929 datum. Please find attached the legend of the maps to show the datum, projection, spheroid, false Northing and Easting, origin etc.
map legend.jpg
I dictate some relevant sentences below:
1. The graticule on this sheet is in terms of The Hong Kong 1929 Datum and is in sympathy with the graticule on the Admiralty Charts of the area
2. Grid data: Universal Transverse Mercator Grid Zone 50
Projection
Transverse Mercator
Spheroid
International
Origin
117° E
Equator
False co-ordinates of origin
500,000 m.E. 0 m.N.
Immediately after loading a scanned tif file, the [Image Rectifier (automatic)] sheet appears.
On [Image Rectifier (automatic)], I click on "Select Projection".
On [Select Control Point Projection], I select
Projection: Transverse Mercator
Datum: since GM does not support the datum "Hong Kong 1929" directly, I suppose I have to click "Add Datum" Planar Units: ??
The Create New Datum sheet appears. Then, I am sorry that I have to ask stupid questions as the parameters showed in the map legend cannot be translated to the parameters that I have to fill in GM directly. Please advise on how to fill in the required parameters.
Datum Name: Hong Kong 1929
Abbreviation (optional): HK1929
Prime Meridian (Degrees): ??
Ellipsoid (Speroid) selection: International 1909 (Hayford/Intl 1924)
Datum Transformation Method:
3-parameter transformation (??)
7-parameter transformation (??)
Custom shift based on control point file (??)
Shifts to WGS84 (meters)
X shift: ??
Y shift: ??
Z shift: ??
Rotation to WGS84 (arc-seconds)
X: ??
Y: ??
Z: ??
Scale correction to WGS84 (parts per million)
Scale (ppm): ??
Please help. Thank you very much.
map legend.jpg
I dictate some relevant sentences below:
1. The graticule on this sheet is in terms of The Hong Kong 1929 Datum and is in sympathy with the graticule on the Admiralty Charts of the area
2. Grid data: Universal Transverse Mercator Grid Zone 50
Projection
Transverse Mercator
Spheroid
International
Origin
117° E
Equator
False co-ordinates of origin
500,000 m.E. 0 m.N.
Immediately after loading a scanned tif file, the [Image Rectifier (automatic)] sheet appears.
On [Image Rectifier (automatic)], I click on "Select Projection".
On [Select Control Point Projection], I select
Projection: Transverse Mercator
Datum: since GM does not support the datum "Hong Kong 1929" directly, I suppose I have to click "Add Datum" Planar Units: ??
The Create New Datum sheet appears. Then, I am sorry that I have to ask stupid questions as the parameters showed in the map legend cannot be translated to the parameters that I have to fill in GM directly. Please advise on how to fill in the required parameters.
Datum Name: Hong Kong 1929
Abbreviation (optional): HK1929
Prime Meridian (Degrees): ??
Ellipsoid (Speroid) selection: International 1909 (Hayford/Intl 1924)
Datum Transformation Method:
3-parameter transformation (??)
7-parameter transformation (??)
Custom shift based on control point file (??)
Shifts to WGS84 (meters)
X shift: ??
Y shift: ??
Z shift: ??
Rotation to WGS84 (arc-seconds)
X: ??
Y: ??
Z: ??
Scale correction to WGS84 (parts per million)
Scale (ppm): ??
Please help. Thank you very much.
Comments
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
Let me know if I can be of further assistance.
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
http://www.geodetic.gov.hk/smo/gsi/Data/pdf/explanatorynotes.pdf
Do you think this can help?
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
Please refer to Grid and Datum section of our website http://www.geodetic.gov.hk/smo/gsi/programs/en/GSS/grid/refdoc.htm to download the 7-parameters "Geodetic Datum Transformation and Map Projection Parameters" for the transformation of Hong Kong 1980 Geodetic Datum to WGS84.
We have to know the reference ellipsoid in working on geodetic / geographical (latitude and longitude) datum. Referring to the footnote of your old map, the Spheroid (i.e. ellipsoid) is International, it is the same reference ellipsoid "International 1910" as the Hong Kong 1980 Geodetic Datum.
So, you can use our 7-parameters shown in "Geodetic Datum Transformation and Map Projection Parameters" for the transformation of your old map to WGS84.
Any comment?
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
I am thinking an alternative way to do this more accurately. The problem is that I only have a scan of the HK1929 datum map. There are referencing grids printed on the map, but to obtain the co-ordinate (in HK1929) of those control points (that I can define the WGS84 co-ordinates accurately), it is very inaccurate just by map reading. I am thinking of using datum of the same ellipsoid as HK1929, say the HK1980, first rectify the HK1929 map into the shape of WGS1984 (using grid intersection as control points). Since HK1929 and HK1980 used the same ellipsoid, the shape of the image of the map, i.e. the projection and scaling, will be the same for the two datum, though the co-ordinate will read differently. After getting the HK1929 map into the shape of WGS84, I can then remove the georeference data from the generated tif image. Then, I can use accurately determined control point file to re-calibrate the co-ordinate of the image. Do you think that this approach can work?
I mean control points
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
I tabulate below the difference between the two datums.
Datum________________Ellipsoid_________________Semi-Major Axis____Flattening
Hong Kong 1929 Datum__Clarke 1880 (RGS)_________6378249.145m_____1/293.465
Hong Kong 1980 Datum__International Hayford 1910__6378388m_________1/297
Any clue for an accurate rectification?
Thanks,
Mike
Global Mapper Support
support@globalmapper.com
Thanks,
Mike
Global Mapper Support
support@globalmapper.com