Can I use Google Earth images for the cadastre?

After a moment of good humor with a Dutch friend today, I rescued some similarity between the process that leads cancer in clinical psychology and the Google Earth romance with the wrong ends:

Stage 1: Scare.

A technician goes to the field in response to a request for measurement from an owner who wishes to sell; Check that there are new buildings that are not visible in the cadastral map. Then he comes to the office and sees that the orthophoto from 40 years ago only shows vineyards in that periphery, with a large plot in rustic conditions.

Call the technician who has been there for 23 for years, aging with a stereoscope hung around his neck and a worn out leroy that only makes a letter letter; After struggling to superimpose one layer over the other, they identify that in fact, in the map there is just what in the image.

So they decide to resort to the novelty of the last year; Google Earth has arrived the year 2004 and shows a colorful orthophoto where the recent buildings appear.

Then the scare comes: The coordinates of that plot do not coincide with those of the map, they are out of phase more than 20 meters.

Be careful-. The quaternary tells him. -These coordinates were made by ancestral aliens, and only they can change them.

Aware that Google can not be this wrong, moves its cadastral layer to match the image. Then he calls his superior and impresses him by showing the digital terrain model that matches the cadastral layer he has exported to Google Earth.

Excited with the novelty, the head of the ejido commission asks you to issue plans of each property, to sell to all the neighbors at a better price «certifications of plots coinciding with Google Earth» ... and now in WGS84! ... SEO optimized!

Stage 2: Denial

Two years later Google appears with an image that says 2006; The technician assumes that the image is more recent, he realizes that the location of the building is almost 6 meters displaced to the south east of where he moved the polygon, now drawn in green.
He finds it surprising that now the coordinates of the maps he has printed are not good either with the original maps or with the new Google image. By then the hand-drawn maps are abandoned in a bathroom that became a warehouse from the day the Quaternary was dismissed.

Your fear becomes a denial, because you can not accept that Google is wrong; not this time. So he leaves the property in question and the whole city where he was moved; waiting for the problem to resolve itself.
It still decides to issue the new certifications based on the new coordinates, with a displacement rounded to 6 meters.

Stage 3: Acceptance

Three years later Google appears with a new image of 2009, and as you can see, the detail is much clearer.
Notice that the building was not the way it had been interpreted.
It coincides with the location of the last year, so it ends up accepting that its parcels are 6 meters displaced .. so it decides to issue other certifications with the displacement, although this time without rounding.
It is surprising that the image has the new building constructed in front of the plot, reason why it arrives at the conclusion that there can not be more precise information; so that it moves all of its 6.47 meters cartography at an inclined angle of -27 degrees.

The old quaternary goes through the office for a purchase sales process and is scared to see that the coordinates are strange. He tries to make suggestions or look for the origin but surrenders after being taught some thematized shapes based on the constructive typology.

Stage 4: Death

He decides to wait one more year, to 2010 and goes to field to make the appraisal of the property whose new construction is in the image. From step to release some wonderful equipment whose advertising is not paid to mention ... 19 precision centimeters, without post processing.
Place the GPS and see that the coordinate is displaced, do another test of 15 and 25 minutes and the coordinate confirms that it is ... quite displaced. Leave the GPS taking a longer reading while greeting the new owner of the building across the street; This invites you to have a coffee in the corridor with a view to the GPS that is cooked in the midday sun for almost 40 minutes.
The neighbor replied that he had bought the property three years ago, and that he had already registered it with the Land Registry, which now requires plans with precise coordinates. UTM WGS84 ... SEO optimized!
With some fear and desire to pee, he asks for the document of the property and this one removes it of the doubts:
He has gone to register the plan with the building certification that he has given to the commission of Ejidos in 2007; And he said thank you for having made the update because now you are sure that the demand that two neighbors have put you will not have justification because it has a recent plan while theirs is more than 30 years.
Take the measurements one, another, another and again. Get a more accurate device, and finally ends convinced of reality:
-The measures of the Google estate are offset 23.87 meters!

3 Replies to "Can I use Google Earth images for the cadastre?"

  1. Care must be taken when using a geographic data source that was not designed for that purpose, especially to support the cadastre, unfortunately Google Earth presents a cluster of satellite images with little rigor in the post processing, that makes the images present some displacement if we compare it with another one from a different year.

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