topic Re: Reprojection and comparison of data in Data Management Questions

Reprojection and comparison of data

LeslieJawili — Mon, 05 Jun 2017 08:03:17 GMT

I would like to seek help in projecting my data to UTM WGS 1984.

DTM attached is in TIF file extracted from WorldDTM with GCS WGS 1984 projection while the other one is in shapefile extracted from CAD data (actual ground survey data) with PTM PRS 92 projection.

i followed the basic steps in reprojecting data but unfortunately i cannot execute it in the right way that it should be projected.

one of my objective is to convert the Shapefile to raster data so i can compare and calculate the difference of elevation in meters of these 2 topographic data.

Please help me on this matter. Attached is my data for reference.

Thank You!

https://community.esri.com/groups/geodatabase?sr=search&searchId=a6c4556b-cf01-4208-8eb8-702bc728aeb8&searchIndex=0‌ https://community.esri.com/community/gis/enterprise-gis?sr=search&searchId=bbbdac94-91cd-4035-b1a3-4ff443982ae9&searchIndex=1‌ https://community.esri.com/groups/coordinate-reference-systems?sr=search&searchId=85a68742-93be-4a70-adeb-7fd96bc9dc75&searchIndex=3‌ https://community.esri.com/groups/technical-support?sr=search&searchId=b3e56eb1-16be-4f3a-a6da-fc0dee40a842&searchIndex=0‌ https://community.esri.com/groups/map-projections?sr=search&searchId=f695d96d-c624-446a-9cc2-5d263471e253&searchIndex=0‌

Re: Reprojection and comparison of data

XanderBakker — Mon, 05 Jun 2017 12:35:17 GMT

You have a number of issues with your data:

The shapefile with the contour lines has a geographic coordinate system defined (coordinates in decimal degrees), however the data really has projected coordinates. It is important to know what the correct coordinate system of this data is and assign that correct coordinate system before you proceed.
The other aspect is that the contour lines, are a result of some cartographic processing (Cul-de-Sac masking). It has holes in the major contour lines. You would need to correct this before interpolation (see Topo to Raster—Help | ArcGIS Desktop, Spatial Analyst or 3D Analyst required):

I also found some residue of the legend in the lower right corner of you contour shapefile:

After you have assigned the correct projection Define Projection—Help | ArcGIS Desktop and have reprojected the data to be in the same projection as the DEM ( Project—Help | ArcGIS Desktop ) you can interpolate the contours Topo to Raster—Help | ArcGIS Desktop and calculate the difference between both DEM's Minus—Help | ArcGIS Desktop

Re: Reprojection and comparison of data

LeslieJawili — Tue, 06 Jun 2017 02:51:30 GMT

ok thank you Mr Xander, i'll clean the data first.

Re: Reprojection and comparison of data

XanderBakker — Tue, 06 Jun 2017 02:57:33 GMT

Do you have any idea on what the correct projection for the contour lines might be?

Re: Reprojection and comparison of data

LeslieJawili — Tue, 06 Jun 2017 03:10:05 GMT

Based on the lay out of CAD file, it is in PRS 92

Re: Reprojection and comparison of data

LeslieJawili — Tue, 06 Jun 2017 03:11:42 GMT

Here's the screen shot of the CAD file legend

Re: Reprojection and comparison of data

NeilAyres — Tue, 06 Jun 2017 08:19:18 GMT

Just looked up that PRS## is for the Philippines. And it is based on the Luzon datum.

There are several zones with their own central meridians. So you need to know which zone.

And use the correct transformation between Luzon and WGS.

Too much detail I'm sure....

Re: Reprojection and comparison of data

LeslieJawili — Tue, 06 Jun 2017 08:31:14 GMT

It falls within PRS Zone 4

Re: Reprojection and comparison of data

LeslieJawili — Tue, 06 Jun 2017 08:33:40 GMT

I'm sorry it's zone 3

Re: Reprojection and comparison of data

NeilAyres — Tue, 06 Jun 2017 08:56:05 GMT

So currently the contour shapefile coord sys is defined like this :

But you can see from the extent tab, that this cannot be true.

Those numbers don't look like decimal degrees to me (too big).

So, redefine it like this:

Right click on the shapefile in Catalog (don't have it open in ArcMap at the same time).

Use the search to find "PRS", in projected coordinate systems.

Re: Reprojection and comparison of data

NeilAyres — Tue, 06 Jun 2017 09:07:22 GMT

Back in ArcMap, looking at the contour data with the online background imagery...

Changed the coord sys of the frame to :

Using this transformation :

Doesn't really fit with the imagery very well. But at this scale (quite large)...

Re: Reprojection and comparison of data

XanderBakker — Tue, 06 Jun 2017 11:41:41 GMT

When I overlay the river with the DEM you can see that it does not match at all.

Perhaps if the vector layer is flipped horizontally and vertically, rotated and perhaps enlarged is may come a bit closer, but you shouldn't do that:

This may be related to the coordinate system of one or both of the inputs and interpolate the contour lines followed by comparing both sources would not make much sense, since this will generate huge differences due to the mismatch of location.

Re: Reprojection and comparison of data

LeslieJawili — Wed, 07 Jun 2017 02:42:36 GMT

Based on your output, what seems to be the problem? Is it the projection of DEM or the ground survey which is in shapefile?

For me it is difficult to compare these 2 since they have different baseline data, i mean different reference point.

Am I right?