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Dear Mr Looi,

I would like to get your clarification on the CRM coordinate and NDCDB coordinate.

A job was carried out with 2 CRM points as datum, and the old stones for the survey lot is observed and proven in position by angle and distance method. the differences between the newly survey coordinates (derived from CRM coordinate) and the NDCDB is within < 0.050m. (around 0.035m)

My question is, during the processing of the ascii files, should i fix the NDCDB coordinate or the CRM coordinate?
I understand that if the differences is more than 0.050m we have to fix the NDCDB coordinate as known point.

Would appreciate your reply to clear my doubts.

Thank you

Regards
Tan

dear sir

according to circular KPUP6/2009 page 31, CRM/GNSS observed points should be used for area that does not has NDCDB and there must be at least 3 points needed as fixed points.

And for area that has the NDCDB, I would recommend you to use the NDCDB coordinate for your computation. That is because our system checking is basing on the NDCDB coordinate. If you use other than the NDCDB coordinate to perform computation and if the different between them is less or equal to 0.05m, then the system will adopt the NDCDB coordinate to perform checking and readjustment.

For time being, I would advise you to perform survey as usual by bearing and distances with proven 3 good marks on the ground. Then use NDCDB coordinate to perform computation and as fixed points. It is exactly like the previous eCoordinate. You just use the value obtained from the eCoordinate to perform computation.

If you would like to use GNSS, then just use the bearing derived from the GNSS’s observed coordinates as datum. If your equipment setting is correct, then we have proven that the bearing derived from GNSS’s observed coordinate compare to azimuth from SUN is in tolerance.

Do not mix around GNSS’s observed coordinates with NDCDB’s coordinates. They wouldn’t be in tolerance. i very happy to hear that you have different around 0.035m from GNSS and NDCDB value (may I know which area you are referring to?). To my experience, I have not come across that kind of result.

Hope you have some clue on what I have derived.

Dear Mr. looi and mr.keanpoh

I also faced the same problem with the CRM and NDCDB. For example, 1st time i checked the lot and the lot surround it, it still don't have the NDCDB coordinate. then, i do the field work, do the CRM observation.

When i want to process the survey data, i re-check the NDCDB availability at that site, then.........the lot that i surveyed still not in NDCDB, but the lot surround it already in NDCDB. In this case, what should i do Mr.looi? do i need to re-surveyed the lot using NDCDB datum format, or i just can go on with the CRM format?

When this happened, i tried to do the comparison with the CRM coordinate that i surveyed with the NDCDB coordinate from the neighborhood lot and i found that it swing equally, about 1.24 meter. The lot was placed at Kelantan.

And about the comparison of bearing observed using GNSS and azimuth from sun, it's true that the result is in the tolerance, the difference is about 3" to 5" ( this is based from my experience).

Its good to have this Help Desk so that we from LS can communicate directly to JUPEM staff like Mr. Looi to solve our problem.

Thanks.

Dear sir

Actually it is an on-going process for jupem to update those PDUK lots into the NDCDB. It is called the COD if you familiar with? That is why some time you will face what you have encountered now; previously don’t have NDCDB lots surrounding but this time got. And that is also why when you log into jupem2u, there is a message on the bottom of the login box reminding you to verify the NDCDB in jupem2u before submitting to jupem.

As from my recommendation previously; you use GNSS’s observed coordinate if surrounding no NDCDB but use NDCDB’s coordinate if surrounding has NDCDB coordinate to perform computation (unless NDCDB is proving wrong) because jupem’s system will check basing on NDCDB.

Since you still survey by bearing/distances and follow PA value, then just plug the NDCDB coordinate from jupem2u to perform computation of the 16 ASCII and submit to jupem. Advisable the NDCDB coordinate is from the 3 good marks you have found. Forget about the CRM that you have done. But to be safe, keep your CRM data as even though you can pass the least square adjustment (LSA) during submission via jupem2u (SUM), it doesn’t mean you can pass the jupem’s internal QC module as the SUM only check the survey relatively. This issue only arise when the NDCDB is in trouble. When this happened, the lot must be in GNSS’s observed coordinates.

Please always remember that if you survey by PA, there is no need to resurvey on the ground. Many people confuse and though need to resurvey. You can start with 3 good marks conventionally or from the CRM as datum. CRM as datum is to say you are using the bearing derived from GNSS’s observed coordinate to start your work but not using this coordinate to perform computation. You still have to find the 3 good marks after that and use these NDCDB coordinates to perform computation and fixed points in TPS. Unless the area no NDCDB lots surrounding, then use the GNSS’s observed coordinate to perform computation, survey still by PA value. The process is exactly like the F2F, you just plug the coordinate from eCordinate to perform computation and send to jupem.

Please also bear in mind, the GNSS’s observed coordinate and the NDCDB’s coordinate cannot be together. For the time being, I hope.

Thanks a lot Mr.Looi for the explanation.

sama sama tuan.

Dear Mr Looi,

sorry for the late reply. but the question above is an example if the differences between the NDCDB and CRM coordinate is less than 0.050m then what i should do. But in reality after surveying the lot, the differences is 0.075m. which i then used the NDCDB coordinate to process the ascii files.
Yes, theres no doubt that 2 CRM points produced by GNSS observation can be used as starting datum.

Thank you for the reply.

dear sir

it is stated very clearly in the SURAT PEKELILING KPUP 1/2010 page 6 for case no. 4.3 “Tanda lama telah dibuktikan berbeza dengan NDCDB melebihi 0.1 m.”

if the different between GNSS and NDCDB is <0.05m, then both also can be used. This is an ideal and the best condition if you can get from the ground.

But if different between GNSS and NDCDB is 0.1m<diff<0.05, then I would advise you to use the NDCDB coordinate. This is because according toKPUP6/2009 page 44, you should determine where is the survey area to meet its condition as follow:

“4.14 Had Anjakan Koordinat
4.14.1 Had anjakan vektor tanda sempadan yang dibenarkan adalah
0.050 meter bagi kawasan bandar/pekan serta pembangunan
baru manakala bagi kawasan lain had anjakan vektor adalah
0.10 meter.”

To tell the truth, I doubt that you can get the above. And always remember that the checking application in JUPEM is basing on the NDCDB coordinate.
That is why I always recommended to use the NDCDB coordinates like what we do from the eCoordinate in F2F.

Hope this is what you look for?