Problems with the Transformation of Coordinates for Cuba
Pablo Velazco Villares <pvela <at> uci.cu>
2010-02-10 01:06:31 GMT
Hello I am entering recently in the list, greetings to the colleagues.
The process of migration of our space databases and applications GIS to platforms of Free Software,
implies in occasions the necessity to repair in aspects that in the software proprietors, they were we
quite transparent. The case that occupies me is a palpable example of what I comment them.
The situation is the following one. I am from Cuba and our CRS in the EPSG they are the following ones: 3795:
North Cuba, 3796: South Cuba, both for the work with plane coordinates, and the 4267 NAD27, for the case of
the geographical ones. The CRS 4267 are the base for the CRS 3795 and 3796 and he has as DATUM the "Nad 27
Continental for US."
In the case of the operations of CONVERSION OF COORDINATED: of 3795 at 3796 or 3796 at 4267 (in this case of
plane to geographical) we achieve extremely precise results in the conversion, but it is not the case,
when we carry out operations of TRANSFORMATION that imply the step the transformation of a DATUM to other,
for example: of NAD27 to WGS84.
The problem is related, with the fact that the specific Datum doesn't exist for the area of Cuba and the local
CRS they are inheriting the parameters of transformation of another region. The problem begins him to
perceive when superimposing space layers as: GPS or Images of Goolgle (both in WGS84), have more than
enough layers in local CRS.
To exemplify the actions that we have carried out, we take like case of study the function Postgis:
ST_Transform and we carry out consultations like these, for the transformation tests. Select
Astext(ST_Transform(ST_SetSRID ('point(-76.670120 20.388508) ':: geometry, 4267),4326));
Previously we carry out the creation of a New SRID (4267001) in the chart: spatial_ref_sys of Postgis,
with: proj4txt: "+proj=longlat +ellps=clrk66 +towgs84=2.478, 149.752, 197.726, -0.526356,
-0.497970, 0.500831, 0.685238 +no_defs ".
As you it can appreciate, we eliminate the parameter +datum=NAD27, and we incorporate those (7)
transformation parameters to WGS84 of our country for the method of Bursa-Wolfe. For what we have studied
on the topic, we lack the treatment of the parameter +nadgrids, that which we have not been able to
implement, because we lack information on the form of configuring an appropriate grill to our territory.